0001193125-26-344532 | 10-Q | XBRL Viewer

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Fair Value Measurements - Summary of Estimated Fair Value Assumptions (Details)	Dec. 31, 2024 yr
Expected Term (in years) \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tranche liability	0.2
Expected Term (in years) \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tranche liability	0.4
Probability of Achievement \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tranche liability	0
Probability of Achievement \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tranche liability	0.80
Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tranche liability	0.09

Condensed Consolidated Statements of Cash Flows (Unaudited) (Parenthetical) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025
Change in fair value of derivative liability	$ 0	$ 1,229
Change in fair value of tranche liability	0	365
Non-cash interest expense		1,443
Loss on extinguishment and on issuance of convertible promissory notes		186
Proceeds from issuance of convertible promissory notes		7,500
Related Party
Change in fair value of derivative liability	0	1,165
Change in fair value of tranche liability	0	331
Non-cash interest expense	0	1,384
Loss on extinguishment and on issuance of convertible promissory notes	0	169
Proceeds from issuance of convertible promissory notes	0	3,402
Premium on issuance of convertible promissory notes	$ 0	$ 169

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Cash flows from operating activities:
Net loss			$ (22,371)	$ (21,546)
Adjustments to reconcile net loss to net cash used in operations:
Depreciation expense			20
Stock-based compensation expense			1,224	965
Change in fair value of derivative liabilities (including $0 and $1,165 for a related party)	$ 0	$ 0	0	(1,229)
Change in fair value of tranche liability (including $0 and $331 for a related party)	0	0	0	(365)
Non-cash interest expense (including $0 and $1,384 for a related party)				1,443
Non-cash operating lease expense			85
Net amortization of premiums and accretion of discounts on marketable securities			(334)
Loss on extinguishment and on issuance of convertible promissory notes (including $0 and $169 for a related party)				186
Changes in assets and liabilities:
Prepaid expenses and other current assets			(1,042)	(588)
Other non-current assets			(796)	(281)
Accounts payable			(232)	2,240
Accrued expenses and other current liabilities			867	(805)
Operating lease liabilities			(48)
Net cash used in operating activities			(22,627)	(19,980)
Cash flows from investing activities:
Purchases of marketable securities			(70,181)
Maturities of marketable securities			40,000
Net cash used in investing activities			(30,181)
Cash flows from financing activities:
Proceeds from the issuance of convertible promissory notes (including $0 and $3,402 from a related party), net of issuance costs				7,500
Cash acquired in connection with the Merger				102,113
Payment of deferred transaction costs and issuance costs			(2,156)	(2,346)
Proceeds from the exercise of stock options			84
Net cash (used in) provided by financing activities			(2,072)	107,267
Net (decrease) increase in cash and cash equivalents and restricted cash			(54,880)	87,287
Cash and cash equivalents and restricted cash, at beginning of the period			98,553	1,639
Cash and cash equivalents and restricted cash, at end of the period	43,673	88,926	43,673	88,926
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	43,173	88,426	43,173	88,426
Restricted cash	500	500	500	500
Total cash, cash equivalents and restricted cash, at end of the period	$ 43,673	$ 88,926	43,673	88,926
Supplemental disclosure of cash flow information:
Unrealized loss on marketable securities			(79)
Deferred transaction and financing issuance costs included in accounts payable and accrued expenses and other current liabilities			$ 75
Premium on issuance of convertible promissory notes (including $0 and $169 for a related party)				186
Merger transaction costs recognized in additional paid-in capital				5,357
Issuance of common stock and equity elimination in connection with the Merger				104,990
Issuance of redeemable convertible preferred stock upon conversion of convertible promissory notes				3,695
Conversion of redeemable convertible preferred stock shares into common stock in connection with the Merger				49,694
Conversion of convertible promissory notes and accrued interest in connection with the Merger				$ 20,799

Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 644	$ 591	$ 1,224	$ 965
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	278	213	446	307
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 366	$ 378	$ 778	$ 658

Fair Value Measurements - Summary of Aggregate Fair Values of Outstanding Level 3 Financial Instruments (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2025 USD ($)
Derivative Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, Beginning	$ 1,042
Initial fair value at issuance	187
Change in fair value	(1,229)
Tranche Liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, Beginning	365
Change in fair value	$ (365)

Merger with AlloVir

6 Months Ended

Jun. 30, 2026

Business Combination [Abstract]

Merger with AlloVir

3. Merger with AlloVir

On March 18, 2025, the Merger closed, and, pursuant to the Merger Agreement, Merger Sub merged with and into Legacy Kalaris with Legacy Kalaris continuing as a wholly owned subsidiary of AlloVir and the surviving corporation of the Merger. Upon completion of the Merger, AlloVir changed its name to “Kalaris Therapeutics, Inc.” and Legacy Kalaris was renamed to “Kalaris Tx, Inc.”

Subject to the terms and conditions of the Merger Agreement, at the Effective Time, all issued and outstanding shares of the Legacy Kalaris’ common stock (including common stock issued upon conversion of Legacy Kalaris’ redeemable convertible preferred stock and outstanding convertible promissory notes, other than the AlloVir Note (as defined below)) converted into the right to receive 0.2016 shares of AlloVir’s common stock calculated in accordance with an exchange ratio equal to 1:0.2016 (the “Exchange Ratio”). Each award of restricted shares of Legacy Kalaris’ common stock that was unvested and outstanding was converted into and exchanged for the right to receive a number of restricted shares of AlloVir common stock based on the Exchange Ratio. Each outstanding option to purchase shares of Legacy Kalaris’ common stock under the Legacy Kalaris’ 2019 Equity Incentive Plan (the “2019 Plan”), whether vested or unvested, was converted into an option to acquire a number of shares of AlloVir’s common stock based on the Exchange Ratio. Exercise prices of assumed options were determined as the product of the exercise price immediately prior to the Effective Time multiplied by the reciprocal of the Exchange Ratio, and rounding up to the nearest whole cent. There were no changes to any other terms of such options or restricted share awards.

Immediately prior to the Effective Time, (i) the outstanding principal and accrued but unpaid interest on convertible promissory notes issued by Legacy Kalaris in January 2025 (other than the AlloVir Note) converted into 794,499 shares of Series B-2 redeemable convertible preferred stock (the “Series B-2 Stock”) at a price of $4.7851 per share, which then converted on a one-for-one basis into shares of Legacy Kalaris common stock, and (ii) the outstanding principal and accrued but unpaid interest on convertible notes issued by Legacy Kalaris in 2024 converted into shares of Legacy Kalaris’ common stock at a price of $6.20 per share.

In January 2025, Legacy Kalaris issued a convertible promissory note in an aggregate principal amount of up to $7.5 million to AlloVir (the “AlloVir Note”) under which AlloVir funded a principal amount of $3.75 million in January 2025. The AlloVir Note accrued interest on the initial advance commencing on the date of such advance, at an interest rate of 8.0% per annum. At the Effective Time, the AlloVir Note was cancelled.

Immediately prior to the Effective Time, each option to purchase shares of AlloVir’s common stock (each, an “AlloVir Option”) that was outstanding immediately prior to the Effective Time, whether vested or unvested, survived the Closing and remains outstanding in accordance with its terms, provided that (i) each unexercised and outstanding AlloVir Option with an exercise price per share equal to or greater than $92.00 was cancelled for no consideration, and (ii) each AlloVir Option that had an exercise price per share less than $92.00, was unvested and unexercised as of the Effective Time, was accelerated in full. Additionally, immediately prior to the Effective Time, each outstanding and unvested AlloVir restricted stock unit was accelerated in full and settled in shares of AlloVir’s common stock.

The aggregate number of shares that AlloVir issued to Legacy Kalaris’ securityholders (including all holders of outstanding convertible notes) at the closing of the Merger was 13,634,744 shares of AlloVir's common stock. Immediately following the Merger, Legacy Kalaris securityholders owned approximately 74.47% of the outstanding shares of the Company’s common stock on a fully-diluted basis and pre-closing AlloVir securityholders owned approximately 25.53% of the outstanding shares of the Company’s

common stock on a fully-diluted basis. The number of shares of the Company's common stock issued and outstanding immediately following the closing of the Merger was as follows:


AlloVir’s common stock outstanding			5,043,652
AlloVir’s restricted stock units accelerated and settled in common stock			24,022
Common stock issued to Legacy Kalaris' securityholders at the Effective Time			13,634,744
			18,702,418

The Merger was accounted for as a reverse recapitalization in accordance with GAAP. Under this method of accounting, Legacy Kalaris was deemed to be the accounting acquirer for financial reporting purposes. This determination was primarily based on the fact that, immediately following the Merger: (1) Legacy Kalaris’ stockholders owned a substantial majority of the voting rights of the Company, inclusive of Samsara; (2) Legacy Kalaris designated a majority of the initial members of the board of directors of the Company; and (3) other than with respect to the Company’s chief financial officer, for which the Company had commenced a search for a qualified candidate, the Company's senior management (which are determined by the board of directors of the Company) held all key positions in senior management of the Company. For accounting purposes, the Merger is treated as the equivalent of Legacy Kalaris issuing stock to acquire the net assets of AlloVir. The reported operating results prior to the Merger are those of Legacy Kalaris. The net assets of AlloVir were recorded at their carrying value in the condensed consolidated financial statements of the Company. Historical common stock share, restricted share awards, common stock options and exercise prices data of Legacy Kalaris have been retroactively recast based on the Exchange Ratio.

AlloVir’s net assets acquired included the following: $102.1 million of cash and cash equivalents, $1.7 million of prepaid expenses and other current assets, and $2.6 million of accounts payable and accrued expenses.

The Company recognized approximately $1.5 million related to AlloVir’s directors’ and officers’ insurance and $0.1 million of share-based compensation expense related to the acceleration of vesting of stock options and restricted stock units as general and administrative expenses at the Effective Time. The Company also incurred transaction costs related to the Merger of approximately $5.4 million, which were recorded as a reduction to additional paid-in capital in the condensed consolidated statement of redeemable convertible preferred stock and stockholders’ equity (deficit) for the six months ended June 30, 2025.

- Definition

The entire disclosure for business combination.

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+ Details

Net Loss Per Share Attributable to Common Stockholders

6 Months Ended

Jun. 30, 2026

Earnings Per Share [Abstract]

Net Loss Per Share Attributable to Common Stockholders

14. Net Loss Per Share Attributable to Common Stockholders

Basic and diluted net loss per share attributable to common stockholders for the three and six months ended June 30, 2026 and 2025 was calculated as follows (in thousands, except share and per share data):


	Three Months Ended June 30,						Six Months Ended June 30,
	2026			2025			2026			2025
Numerator:
Net loss attributable to common stockholders, basic and diluted	$	(11,515	)	$	(11,350	)	$	(22,371	)	$	(21,546	)
Denominator:
Weighted-average common shares outstanding		23,797,306			18,702,418			23,760,665			11,419,020
Less: Weighted-average common shares subject to repurchase		—			(1,132	)		—			(1,343	)
Weighted-average shares outstanding, basic and diluted		23,797,306			18,701,286			23,760,665			11,417,677
Net loss per share attributable to common stockholders, basic and diluted	$	(0.48	)	$	(0.61	)	$	(0.94	)	$	(1.89	)

As described in Note 12, the Pre-Funded Warrants to purchase up to an aggregate of 800,000 shares of the Company's common stock at a purchase price of $9.9999 per Pre-Funded Warrant were classified as a component of equity in the Company's condensed consolidated balance sheets upon entering the 2025 Securities Purchase Agreement because they were freestanding financial instruments that were immediately exercisable, did not embody an obligation for the Company to repurchase its own shares, and entitled the holder to receive a fixed number of shares of common stock upon exercise. All of the shares underlying the Pre-Funded Warrants were included in the weighted-average number of shares of common stock used to calculate basic and diluted net loss per common share upon entering the 2025 Securities Purchase Agreement because the shares may have been issued for little or no consideration, were fully vested, and were exercisable after the original issuance date of the Pre-Funded Warrants. On April 13, 2026, all of the Pre-Funded Warrants were exercised on a cashless basis, resulting in the issuance of 799,987 shares of the Company’s common stock. As of June 30, 2026, no Pre-Funded Warrants remained outstanding.

The potential shares of common stock were excluded from the computation of diluted net loss per share attributable to common stockholders as of June 30, 2026 and 2025 because including them would have had an anti-dilutive effect. The excluded shares were as follows:


	June 30,
	2026		2025
Outstanding options to purchase common stock		2,535,975		1,988,633
Unvested restricted stock awards		—		991
Total		2,535,975		1,989,624

Merger with AlloVir (Tables)

6 Months Ended

Jun. 30, 2026

Business Combination [Abstract]

Schedule of Number of Shares Common Stock Issued and Outstanding

The number of shares of the Company's common stock issued and outstanding immediately following the closing of the Merger was as follows:


AlloVir’s common stock outstanding			5,043,652
AlloVir’s restricted stock units accelerated and settled in common stock			24,022
Common stock issued to Legacy Kalaris' securityholders at the Effective Time			13,634,744
			18,702,418

Marketable Securities - Summary of Amortized Cost and Estimated Fair Value of Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 50,438	$ 19,922
Unrealized Losses	(73)
Unrealized Gains		6
Estimated Fair Value	50,365	19,928
U.S. Government Treasury Securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost Short-term	50,438	19,922
Unrealized Losses Short-term	(73)
Unrealized Gains Short-term		6
Estimated Fair Value Short-term	$ 50,365	$ 19,928

Stockholders' Equity (Deficit) (Tables)

6 Months Ended

Jun. 30, 2026

Equity [Abstract]

Schedule of Common Stock Reserved for Future Issuance

Common Stock

As of June 30, 2026 and December 31, 2025, shares of common stock reserved for future issuance were as follows:


	June 30,		December 31,
	2026		2025
Outstanding stock option awards		2,535,975		2,142,278
Pre-funded warrants to purchase common stock		—		800,000
Shares available for future options grants under the Equity Plans		1,959,250		1,310,403
Shares available for grant under the 2020 ESPP		172,487		119,326
Total shares reserved for future issuance		4,667,712		4,372,007

Summary of Significant Accounting Policies - Additional Information (Details)	6 Months Ended
	Jun. 30, 2026
Summary Of Significant Accounting Policies [Line Items]
Common stock exchange ratio	0.2016
Short-term investments maturity period	1 year

Net Loss Per Share Attributable to Common Stockholders (Tables)

6 Months Ended

Jun. 30, 2026

Earnings Per Share [Abstract]

Computation Of Basic And Diluted Net Loss Per Share Attributable To Common Stockholders


	Three Months Ended June 30,						Six Months Ended June 30,
	2026			2025			2026			2025
Numerator:
Net loss attributable to common stockholders, basic and diluted	$	(11,515	)	$	(11,350	)	$	(22,371	)	$	(21,546	)
Denominator:
Weighted-average common shares outstanding		23,797,306			18,702,418			23,760,665			11,419,020
Less: Weighted-average common shares subject to repurchase		—			(1,132	)		—			(1,343	)
Weighted-average shares outstanding, basic and diluted		23,797,306			18,701,286			23,760,665			11,417,677
Net loss per share attributable to common stockholders, basic and diluted	$	(0.48	)	$	(0.61	)	$	(0.94	)	$	(1.89	)

Potential Dilutive Securities Excluded From Computation Of Diluted Net Loss Per Share Attributable To Common Stockholders


	June 30,
	2026		2025
Outstanding options to purchase common stock		2,535,975		1,988,633
Unvested restricted stock awards		—		991
Total		2,535,975		1,989,624

Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2026

Share-Based Payment Arrangement [Abstract]

Summary of Stock Option Activity

A summary of option activity under the Equity Plans for the six months ended June 30, 2026 is as follows:


	Outstanding Awards
	Number of Shares Underlying Outstanding Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2025		2,142,278		$	3.98		8.88	$	9,552
Options granted		892,420			6.61
Options exercised		(102,576	)		0.84				581
Options cancelled		(396,147	)		5.05
Outstanding, June 30, 2026		2,535,975			4.87		8.74		2,666
Shares exercisable		849,138			3.07		8.00		1,780
Vested and expected to vest, June 30, 2026		2,535,975		$	4.87		8.74	$	2,666

Summary of RSAs Activity

A summary of RSAs activity under the 2019 Plan for the six months ended June 30, 2026 is as follows:


	Restricted Stock Awards			Weighted-Average Grant Date Fair Value
Unvested as of December 31, 2025		141		$	1.74
Vested		(141	)		1.74
Unvested as of June 30, 2026		—			—

No RSAs were granted during the three and six months ended June 30, 2026 and 2025. The total fair value of RSAs vested during the three and six months ended June 30, 2026 and 2025 was immaterial. No RSAs were repurchased or cancelled during the three and six months ended June 30, 2026 and 2025.

Schedule of Stock-based Compensation Expense

Stock-based compensation expense included in the Company’s condensed consolidated statements of operations and comprehensive loss for the three and six months ended June 30, 2026 and 2025 is as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2026		2025		2026		2025
Research and development expenses	$	278	$	213	$	446	$	307
General and administrative expenses		366		378		778		658
Total stock-based compensation expense	$	644	$	591	$	1,224	$	965

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Jun. 30, 2026	Mar. 31, 2026	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2026	Jun. 30, 2025
Pay vs Performance Disclosure
Net Income (Loss)	$ (11,515)	$ (10,856)	$ (11,350)	$ (10,196)	$ (22,371)	$ (21,546)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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+ Details

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2026

Fair Value Disclosures [Abstract]

Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis

The Company’s fair value hierarchy for its financial instruments measured at fair value on a recurring basis as of June 30, 2026 and December 31, 2025, were as follows (in thousands):


	Fair Value Measurements
As of June 30, 2026	Total		Level 1		Level 2		Level 3
Cash equivalents:
Money market funds	$	41,696	$	41,696	$	—	$	—
U.S. government treasury securities		—		—		—		—
Total cash equivalents	$	41,696	$	41,696	$	—	$	—
Short-term marketable securities:
U.S. government treasury securities	$	50,365	$	50,365	$	—	$	—
Total marketable securities	$	92,061	$	92,061	$	—	$	—


	Fair Value Measurements
As of December 31, 2025	Total		Level 1		Level 2		Level 3
Cash equivalents:
Money market funds	$	94,394	$	94,394	$	—	$	—
U.S. government treasury securities		—		—		—		—
Total cash equivalents	$	94,394	$	94,394	$	—	$	—
Short-term marketable securities:
U.S. government treasury securities	$	19,928	$	19,928	$	—	$	—
Total marketable securities	$	19,928	$	19,928	$	—	$	—

Summary of Estimated Fair Value

The following assumptions were used to determine the estimated fair value of the derivative liabilities related to the redemption features as of the issuance dates:


		At Issuance Date (January 10, 2025)
Expected term (in years)		0.2 – 0.3
Probability of achievement		0.0% – 80.0%
Discount rate		8.50%

The following assumptions were used to determine the estimated fair value of the derivative liabilities related to the redemption features as of the issuance date and as of December 31, 2024:


	Issuance Dates	December 31, 2024
Expected term (in years)	0.4 – 1.3	0.2 – 0.4
Probability of achievement	0.0% – 90.0%	0.0% – 80.0%
Discount rate	9.5% – 18.7%	9.0%

The significant assumptions were as follows as of December 31, 2024:


		December 31, 2024
Expected term (in years)		0.2 - 0.4
Probability of achievement		0.0% - 80.0%
Discount rate		9.0%

Summary of Aggregate Fair Values of Outstanding Level 3 Financial Instruments

The following table provides a roll-forward of the aggregate fair values of the Company’s outstanding Level 3 financial instruments during the six months ended June 30, 2025 (in thousands):


	Derivative liabilities			Tranche liability
Balance as of December 31, 2024	$	1,042		$	365
Initial fair value at issuance		187			—
Change in fair value		(1,229	)		(365	)
Balance as of June 30, 2025	$	—		$	—

Merger with AlloVir - Additional Information (Details) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 18, 2025 USD ($) $ / shares shares	Jan. 31, 2025 USD ($) $ / shares shares	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2026 USD ($) $ / shares	Jun. 30, 2025 USD ($)	Jan. 31, 2024 $ / shares shares
Business Acquisition [Line Items]
Exercise price per share, cancelled \| $ / shares					$ 5.05
Stock-based compensation expense			$ 644	$ 591	$ 1,224	$ 965
General and Administrative
Business Acquisition [Line Items]
Stock-based compensation expense			$ 366	$ 378	$ 778	$ 658
AlloVir
Business Acquisition [Line Items]
Merger agreement date	Mar. 18, 2025
Interest rate		8.00%
Equity own percentage	25.53%
Cash and cash equivalents	$ 102,100
Prepaid expenses and other current assets	1,700
Accounts payable and accrued expenses	2,600
Director's and officer's insurance recognized	1,500
Transaction costs	$ 5,400
AlloVir \| Common Stock
Business Acquisition [Line Items]
Common stock shares issued \| shares	13,634,744
AlloVir \| Stock Options \| General and Administrative
Business Acquisition [Line Items]
Stock-based compensation expense	$ 100
AlloVir \| Restricted Stock Units \| General and Administrative
Business Acquisition [Line Items]
Stock-based compensation expense	$ 100
Kalaris Therapeutics, Inc.
Business Acquisition [Line Items]
Equity own percentage	74.47%
Series B-2 Redeemable Convertible Preferred Stock
Business Acquisition [Line Items]
Redeemable convertible preferred stock, shares issued \| shares							1,280,000
Price per share \| $ / shares							$ 1.25
2024 Convertible Promissory Note \| Kalaris Therapeutics, Inc.
Business Acquisition [Line Items]
Common stock price per share \| $ / shares		$ 6.2
Debt instrument, issued, principal amount		$ 3,750
2024 Convertible Promissory Note \| Redeemable Convertible Preferred Stock \| AlloVir
Business Acquisition [Line Items]
Redeemable convertible preferred stock, shares issued \| shares	0.2016
Conversion ratios	4.9603
2024 Convertible Promissory Note \| Series B-2 Redeemable Convertible Preferred Stock \| Kalaris Therapeutics, Inc.
Business Acquisition [Line Items]
Redeemable convertible preferred stock, shares issued \| shares		794,499
Price per share \| $ / shares		$ 4.7851
Conversion ratios		1
Maximum \| AlloVir
Business Acquisition [Line Items]
Exercise price per share unvested and unexercised \| $ / shares	$ 92
Maximum \| 2024 Convertible Promissory Note \| AlloVir
Business Acquisition [Line Items]
Debt instrument, issued, principal amount		$ 7,500
Minimum \| AlloVir
Business Acquisition [Line Items]
Exercise price per share, cancelled \| $ / shares	$ 92

Fair Value Measurements - Summary of Estimated Fair Value of Derivative Liabilities Related to Redemption Features (Details)	Jan. 10, 2025 yr	Dec. 31, 2024 yr	Mar. 31, 2024 yr
Expected Term (in years) \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0.2	0.2	0.4
Expected Term (in years) \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0.3	0.4	1.3
Probability of Achievement \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0	0	0
Probability of Achievement \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0.80	0.80	0.90
Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0.085	0.09
Discount Rate \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities			0.095
Discount Rate \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities			0.187

Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2026
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). AlloVir and its subsidiaries’ operating results are included in the Company’s condensed consolidated financial statements from the Closing Date of the Merger. All other accompanying financial data as of December 31, 2025, and for the three and six months ended June 30, 2025, include only the accounts and disclosures of Legacy Kalaris. All intercompany transactions and balances have been eliminated upon consolidation. These unaudited condensed consolidated financial statements and the notes accompanying them should be read in conjunction with Legacy Kalaris' audited financial statements as of and for the year ended December 31, 2025, included in the Company’s Annual Report on Form 10-K filed with the SEC on March 17, 2026. All historical common share data and per-share amounts prior to the Merger were retrospectively recast to reflect the effect of the exchange ratio of 0.2016 per one share, which was determined in accordance with the Merger Agreement. The number of authorized shares and par value per share were not recast. The conversion ratios for each series of redeemable convertible preferred stock, which were converted into shares of common stock in connection with the closing of the Merger, were proportionally recast.
Unaudited Condensed Financial Statements	Unaudited Condensed Financial Statements The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair statement of the Company’s financial position as of June 30, 2026 and its results of operations and its cash flows for the three and six months ended June 30, 2026 and 2025. The results of operations for the three and six months ended June 30, 2026 and 2025 are not necessarily indicative of the results to be expected for the year ending December 31, 2026, or for any other future annual or interim period. The consolidated balance sheet as of December 31, 2025 included herein was derived from the audited financial statements as of that date. Certain information and footnote disclosures normally included in consolidated financial statements prepared in accordance with GAAP have been condensed or omitted from these unaudited condensed consolidated financial statements.
Marketable Securities	Marketable Securities The Company classifies all investments with a remaining maturity of less than one year as short-term marketable securities and investments with a remaining maturity of greater than one year as long-term marketable securities. Marketable securities consist of U.S. treasury securities classified as available-for-sale. The Company's marketable securities are classified as available-for-sale as they are available to fund current operations, even if the Company intends to hold the marketable securities to maturity. Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in other comprehensive income (loss) until realized. The amortized cost of debt securities in this category is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization or accretion is included in other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. Realized gains and losses are determined using the specific identification method and are included in other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. Interest on available-for-sale securities is included in other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. The Company reviews its portfolio of marketable securities, using both quantitative and qualitative factors, to determine if declines in fair value below cost have resulted from a credit-related loss. If the decline in fair value is due to credit-related factors, a loss is recognized in other income (expense).
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40) In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses to improve financial reporting by requiring that public business entities disclose additional information about specific expense categories in the notes to financial statements at interim and annual reporting periods. The amendments in this ASU do not change or remove current expense disclosure requirements; however, the amendments affect where such information appears in the notes to the financial statements because entities are required to include certain current disclosures in the same tabular format as the other disaggregation requirements in the amendments. This ASU is effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027. Early adoption is permitted. The Company is currently evaluating the impact that the updated standard will have on its consolidated financial statement disclosures and financial reporting processes. ASU 2025-06, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40) In September 2025, the FASB issued ASU 2025-06, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software to modernize the accounting for software costs and increase the operability of the recognition guidance considering different methods of software development. The amendments are effective for annual reporting periods beginning after December 15, 2027, and interim reporting periods within those annual reporting periods. Early adoption is permitted as of the beginning of an annual reporting period. The Company is currently evaluating the impact that the updated standard will have on its consolidated financial statement disclosures.

Stock-Based Compensation - Summary of RSAs Activity (Details) - Restricted Common Stock - 2019 Plan	6 Months Ended
	Jun. 30, 2026 $ / shares shares
Number of Shares
Restricted Stock Awards, Unvested as of December 31, 2025 \| shares	141
Restricted Stock Awards, Vested \| shares	(141)
Restricted Stock Awards, Unvested as of June 30, 2026 \| shares	0
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Unvested as of December 31, 2025 \| $ / shares	$ 1.74
Weighted Average Grant Date Fair Value, Vested \| $ / shares	1.74
Weighted Average Grant Date Fair Value, Unvested as of June 30, 2026 \| $ / shares	$ 0

Net Loss Per Share Attributable to Common Stockholders - Potential Dilutive Securities Excluded From Computation Of Diluted Net Loss Per Share Attributable To Common Stockholders (Details) - shares	6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	2,535,975	1,989,624
Options To Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	2,535,975	1,988,633
Unvested Restricted Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		991

Stock-Based Compensation

6 Months Ended

Jun. 30, 2026

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

13. Stock-Based Compensation

Equity Plans

At the closing of the Merger, the Company assumed the 2019 Plan.

In connection with the Merger, AlloVir’s stockholders approved an amendment to AlloVir’s 2020 Stock Option and Grant Plan (as amended, the “2020 Plan” and together with the 2019 Plan, the “Equity Plans”) to increase the number of shares reserved for future issuance under the 2020 Plan, which is subject to an annual increase on January 1 of each year from 2026 and thereafter, such that the number of shares of common stock reserved and available for issuance under the 2020 Plan is cumulatively increased by 5% of the number of shares of common stock issued and outstanding on the immediately preceding December 31, or such lesser number of shares as approved by the plan administrator; to establish the maximum aggregate number of shares of stock that may be issued in the form of incentive stock options (“ISOs”) shall not exceed 15,250,000 and to extend the term of the 2020 Plan to the tenth anniversary of the closing of the Merger.

Under the Equity Plans, the Company may grant ISOs, nonqualified stock options (“NSO”), restricted stock awards (“RSAs”), restricted stock unit awards and other stock awards to the Company’s employees, officers, non-employee directors, consultants, and advisors. Options to purchase common stock may be granted at a price not less than the fair market value as established by the board of directors in the case of both NSOs and ISOs. Stock option grants under the Equity Plans generally vest over four years. All options expire no later than ten years from the date of grant. The exercise price of ISOs granted to an employee who owns more than 10% of the voting power of all classes of stock of the Company shall be no less than 110% of the estimated fair market value of the underlying common stock on the grant date, and the contractual term is no longer than five years.

As of June 30, 2026, 1,588,703 shares of common stock had been authorized for issuance and 434,158 shares were available for future grants under the 2019 Plan and 3,414,594 shares of common stock had been authorized for issuance and 1,525,092 shares were available for future grants under the 2020 Plan.

Stock Options

The Company has granted stock options with service-based vesting conditions. Stock options typically vest over four years and have a maximum term of ten years. The Company typically grants stock options to employees and non-employees at exercise prices deemed to be equal to the fair value of the common stock at the time of grant.

The Black-Scholes option pricing model, used to estimate the fair value of stock-based awards, requires the use of the following assumptions:

•

Fair Value of Common Stock. Prior to the Merger, the fair market value of Legacy Kalaris’ common stock was determined by the board of directors of Legacy Kalaris with assistance from management of Legacy Kalaris and external valuation experts. The approach to estimating the fair market value of common stock is consistent with the methods outlined in the American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately- Held-Company Equity Securities Issued as Compensation. After the closing of the Merger, the fair value of common stock is the Company’s closing price per share on the Nasdaq Global Market on the grant date.

•

Expected Term. The expected term of options granted represents the period of time that the options are expected to be outstanding. Due to the lack of historical exercise history, the expected term of the Company’s employee and non-employee stock options has been determined by calculating the midpoint of the contractual term of the options and the weighted-average vesting period.

•

Expected Volatility. The expected stock price volatility assumption was determined by examining the historical volatilities for comparable public companies, as the Company has limited trading history for the common stock.

•

Risk-Free Interest Rate. The risk-free interest rate assumption is based on the U.S. Treasury zero-coupon issued in effect at the time of grant for periods corresponding with the expected term of the option.

•

Dividends. The Company has not paid any dividends on its common stock since inception and does not anticipate paying any dividends in the foreseeable future. Consequently, an expected dividend yield of zero was used.

A summary of option activity under the Equity Plans for the six months ended June 30, 2026 is as follows:


	Outstanding Awards
	Number of Shares Underlying Outstanding Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2025		2,142,278		$	3.98		8.88	$	9,552
Options granted		892,420			6.61
Options exercised		(102,576	)		0.84				581
Options cancelled		(396,147	)		5.05
Outstanding, June 30, 2026		2,535,975			4.87		8.74		2,666
Shares exercisable		849,138			3.07		8.00		1,780
Vested and expected to vest, June 30, 2026		2,535,975		$	4.87		8.74	$	2,666

Aggregate intrinsic value represents the difference between the fair value of the underlying common stock and the exercise price as of June 30, 2026. 102,576 shares were exercised during the six months ended June 30, 2026, and no shares were exercised during the six months ended June 30, 2025. The weighted-average fair value per share of options exercised during six months ended June 30, 2026 and 2025 was $2.90 and immaterial, respectively. The aggregate intrinsic value of options exercised during the six months ended June 30, 2026 and 2025 was $0.6 million and immaterial, respectively.

The total fair value of options that vested during the six months ended June 30, 2026 and 2025 was $1.7 million and $0.5 million, respectively. No options were granted during the three months ended June 30, 2025. As of June 30, 2026 the total unrecognized stock-based compensation expense was $8.1 million, which is expected to be recognized over a weighted-average period of 2.9 years.

RSAs

In February 2022, the Company issued RSAs to its former president for 203,670 shares and a consultant for 13,577 shares, in each case, at a purchase price of $0.005 per share under the 2019 Plan. The shares related to each of the former president’s award and the consultant's awards are fully vested. The Company issued one share of common stock for each whole RSA that vested, subject to satisfaction of the employee's tax withholding obligations. Shares purchased pursuant to these awards participate in dividends and voting, are legally outstanding, and are presented as outstanding shares; however, for accounting purposes, shares purchased by employees pursuant to RSAs are not considered issued until they vest according to their respective vesting schedules. Proceeds received from the issuance of RSAs are recorded as a share repurchase liability within accrued expenses and other current liabilities on the condensed consolidated balance sheet and reclassified to additional paid-in capital when the awards vested.

A summary of RSAs activity under the 2019 Plan for the six months ended June 30, 2026 is as follows:


	Restricted Stock Awards			Weighted-Average Grant Date Fair Value
Unvested as of December 31, 2025		141		$	1.74
Vested		(141	)		1.74
Unvested as of June 30, 2026		—			—

2020 Employee Stock Purchase Plan

The Company can issue common stock shares to its employees under the 2020 Employee Stock Purchase Plan (the “2020 ESPP”). The number of shares of common stock reserved and available for issuance under the 2020 ESPP is cumulatively increased on each January 1 by the lesser of (i) 53,161 shares of common stock, (ii) 1% of the number of shares of common stock issued and outstanding on the immediately preceding December 31, and (iii) such number of shares of common stock as determined by the plan administrator. On June 30, 2026, there was an aggregate of 172,487 shares reserved for future issuance under the 2020 ESPP.

The ESPP allows eligible employees to authorize payroll deductions of up to 15% of their base salary or wages up to $25,000 annually to be applied toward the purchase of shares of the Company's common stock on the last trading day of the offering period. Participating employees will purchase shares of the Company's common stock at a discount of up to 15% on the lesser of the closing price of the Company's common stock on the Nasdaq Global Market (i) on the first trading day of the offering period or (ii) the last day of any offering period. The Company utilizes the Black Scholes option pricing model to compute the fair market value of the shares and stock-based compensation expense is recognized over the offering period. Six-month offering periods commence each January 1 and July 1 during the term of the plan, with the plan administrator having the right to establish different offering periods.

The Company did not issue shares of common stock under the 2020 ESPP during the three and six months ended June 30, 2026.

Stock-Based Compensation Expense


	Three Months Ended June 30,				Six Months Ended June 30,
	2026		2025		2026		2025
Research and development expenses	$	278	$	213	$	446	$	307
General and administrative expenses		366		378		778		658
Total stock-based compensation expense	$	644	$	591	$	1,224	$	965

Nature of the Business - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2026	Mar. 31, 2026	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net loss	$ (11,515)	$ (10,856)	$ (11,350)	$ (10,196)	$ (22,371)	$ (21,546)
Cash flows from operating activities					(22,627)	$ (19,980)
Accumulated deficit	(182,370)				(182,370)		$ (159,999)
Cash, cash equivalents and marketable securities	$ 93,500				$ 93,500

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

Net Loss Per Share Attributable to Common Stockholders - Computation Of Basic And Diluted Net Loss Per Share Attributable To Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2026	Mar. 31, 2026	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2026	Jun. 30, 2025
Numerator:
Net loss	$ (11,515)	$ (10,856)	$ (11,350)	$ (10,196)	$ (22,371)	$ (21,546)
Denominator:
Weighted average common shares outstanding	23,797,306		18,702,418		23,760,665	11,419,020
Less: Weighted-average common shares subject to repurchase	0		(1,132)		0	(1,343)
Weighted-average shares outstanding - basic	23,797,306		18,701,286		23,760,665	11,417,677
Weighted-average shares outstanding - diluted	23,797,306		18,701,286		23,760,665	11,417,677
Net loss per share attributable to common stockholders - basic	$ (0.48)		$ (0.61)		$ (0.94)	$ (1.89)
Net loss per share attributable to common stockholders - diluted	$ (0.48)		$ (0.61)		$ (0.94)	$ (1.89)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Balance Sheet Components - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Payables and Accruals [Abstract]
Accrued research and development expenses	$ 5,901	$ 4,295
Accrued compensation expense	865	1,601
Accrued professional and legal costs	466	442
Accrued transaction expenses		1,717
Other accrued expenses and other current liabilities	35	62
Total accrued expenses and other current liabilities	$ 7,267	$ 8,117

Balance Sheet Components

6 Months Ended

Jun. 30, 2026

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Components

6. Balance Sheet Components

Prepaid expenses and other current assets

Prepaid expenses and other current assets as of June 30, 2026 and December 31, 2025 consisted of the following (in thousands):


	June 30,		December 31,
	2026		2025
Prepaid research and development expenses	$	778	$	323
Prepaid insurance		509		185
Prepaid taxes		365		211
Prepaid professional and legal costs		—		30
Other prepaid expenses and other current assets		217		78
Total prepaid expenses and other current assets	$	1,869	$	827

Accrued expenses and other current liabilities

Accrued expenses and other current liabilities as of June 30, 2026 and December 31, 2025 consisted of the following (in thousands):


	June 30,		December 31,
	2026		2025
Accrued research and development expenses	$	5,901	$	4,295
Accrued compensation expense		865		1,601
Accrued professional and legal costs		466		442
Accrued transaction expenses		—		1,717
Other accrued expenses and other current liabilities		35		62
Total accrued expenses and other current liabilities	$	7,267	$	8,117

Marketable Securities - Additional Information (Details) - USD ($)	Jun. 30, 2026	Dec. 31, 2025
Debt Securities, Available-for-Sale [Line Items]
Available-for-sale securities in continuous unrealized loss position for greater than 12 months	$ 0	$ 0
Marketable securities	$ 50,365,000	$ 19,928,000

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

Stockholders' Equity (Deficit) - Schedule of Common Stock Reserved for Future Issuance (Details) - shares	Jun. 30, 2026	Dec. 31, 2025
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	4,667,712	4,372,007
Pre-Funded Warrants [Member]
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	0	800,000
2020 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	172,487
Stock Options
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	2,535,975	2,142,278
Stock Available For Grant \| Options Grants under Equity Plans
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	1,959,250	1,310,403
Stock Available For Grant \| 2020 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	172,487	119,326

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

Leases - Schedule of Operating Lease on Its Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Assets:
Operating lease right-of-use assets	$ 1,389	$ 1,475
Current liabilities:
Operating lease liability, current	347	316
Noncurrent Liabilities:
Operating lease liability, long-term	1,053	$ 1,132
Total lease liabilities	$ 1,400

Redeemable Convertible Preferred Stock - Additional Information (Details) - Series B-2 $ / shares in Units, $ in Millions	1 Months Ended
	Jan. 31, 2024 USD ($) $ / shares shares
Temporary Equity [Line Items]
Shares issued \| shares	1,280,000
Price per share \| $ / shares	$ 1.25
Gross cash proceeds \| $	$ 1.6

Convertible Promissory Notes - Additional Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended					6 Months Ended
	Jan. 31, 2025 USD ($)	Nov. 30, 2024 USD ($)	Oct. 31, 2024 USD ($)	May 31, 2024 USD ($)	Mar. 31, 2024 USD ($)	Jun. 30, 2026 USD ($) $ / shares shares	Jun. 30, 2025 USD ($)	Dec. 31, 2024
Short-Term Debt [Line Items]
Issuance of conversion of convertible promissory notes							$ 3,695
Kalaris Therapeutics, Inc. \| Series B-2 Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Debt instrument, converted ratio						1
Maximum \| Kalaris Therapeutics, Inc.
Short-Term Debt [Line Items]
Issuance of conversion of convertible promissory notes			$ 7,500
Probability of Achievement \| Minimum
Short-Term Debt [Line Items]
Tranche liability								0
Probability of Achievement \| Maximum
Short-Term Debt [Line Items]
Tranche liability								0.80
Discount Rate
Short-Term Debt [Line Items]
Tranche liability								0.09
2024 Convertible Promissory Note
Short-Term Debt [Line Items]
Outstanding principal amount						$ 10,000
Interest rate					10.00%
Aggregate advance				$ 10,000	$ 5,000
Maturity date					2025-03
Estimated fair value					$ 12,100
Change in the fair value of derivative liability							500
Loss on issuance of convertible promissory notes							(200)
Interest expense							800
Contractual interest expense							200
Amortization of debt discount							600
Total premium on debt					2,100
Accrued interest						$ 900
Common shares issued for conversion of debt \| shares						1,757,951
Conversion price per share \| $ / shares						$ 6.2
2024 Convertible Promissory Note \| Kalaris Therapeutics, Inc.
Short-Term Debt [Line Items]
Debt instrument, issued, principal amount	$ 3,750
2024 Convertible Promissory Note \| Maximum
Short-Term Debt [Line Items]
Outstanding principal amount					$ 10,000
2024 Bridge Notes
Short-Term Debt [Line Items]
Outstanding principal amount		$ 5,000				$ 10,000
Interest rate		8.00%
Maturity date			2025-05
Change in the fair value of derivative liability							500
Recognized gain for change in fair value of tranche liability							400
Total fair value at issuance of derivative instrument			$ 1,000
Accrued interest						$ 300
Common shares issued for conversion of debt \| shares						1,660,888
Conversion price per share \| $ / shares						$ 6.2
Debt instrument, issued, principal amount		$ 1,000	9,000
Additional draw up amount		$ 15,000
2024 Bridge Notes \| Maximum
Short-Term Debt [Line Items]
Outstanding principal amount			15,000
Debt instrument, issued, principal amount			25,000
2025 Bridge Notes
Short-Term Debt [Line Items]
Outstanding principal amount	3,900					$ 3,750
Change in the fair value of derivative liability							200
Total fair value at issuance of derivative instrument	$ 200
Accrued interest						$ 100
Per share price paid by investors	8.50%
2025 Bridge Notes \| Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Difference between the fair value at the issuance date and the principal amount of the note	$ 200
2025 Bridge Notes \| Series B-2 Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Outstanding principal amount	$ 3,750
Common shares issued for conversion of debt \| shares						794,499
Conversion price per share \| $ / shares						$ 4.7851
2025 Bridge Notes \| Minimum
Short-Term Debt [Line Items]
Expected term (in years)	2 months 12 days
2025 Bridge Notes \| Maximum
Short-Term Debt [Line Items]
Expected term (in years)	3 months 18 days
2025 Bridge Notes \| Probability of Achievement \| Minimum
Short-Term Debt [Line Items]
Tranche liability	0.20
2025 Bridge Notes \| Probability of Achievement \| Maximum
Short-Term Debt [Line Items]
Tranche liability	0.80
2025 Bridge Notes \| Tranche \| Series B-2 Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Additional draw up amount	$ 5,000
2025 Bridge Notes \| First and Second Tranches \| Series B-2 Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Additional draw up amount	3,750
2025 Bridge Notes \| Third Tranches \| Series B-2 Redeemable Convertible Preferred Stock
Short-Term Debt [Line Items]
Additional draw up amount	7,500
2024 Bridge Notes and 2025 Bridge Notes
Short-Term Debt [Line Items]
Interest expense							600
Contractual interest expense							200
Amortization of debt discount							$ 400
January 2025 AlloVir Convertible Promissory Note
Short-Term Debt [Line Items]
Outstanding principal amount	$ 3,750
AlloVir Note \| Kalaris Therapeutics, Inc.
Short-Term Debt [Line Items]
Common shares issued for conversion of debt \| shares						160,165
AlloVir Note \| Maximum
Short-Term Debt [Line Items]
Issuance of conversion of convertible promissory notes			$ 7,500

Fair Value Measurements

6 Months Ended

Jun. 30, 2026

Fair Value Disclosures [Abstract]

Fair Value Measurements

5. Fair Value Measurements

The Company’s fair value hierarchy for its financial instruments measured at fair value on a recurring basis as of June 30, 2026 and December 31, 2025, were as follows (in thousands):


	Fair Value Measurements
As of June 30, 2026	Total		Level 1		Level 2		Level 3
Cash equivalents:
Money market funds	$	41,696	$	41,696	$	—	$	—
U.S. government treasury securities		—		—		—		—
Total cash equivalents	$	41,696	$	41,696	$	—	$	—
Short-term marketable securities:
U.S. government treasury securities	$	50,365	$	50,365	$	—	$	—
Total marketable securities	$	92,061	$	92,061	$	—	$	—


	Fair Value Measurements
As of December 31, 2025	Total		Level 1		Level 2		Level 3
Cash equivalents:
Money market funds	$	94,394	$	94,394	$	—	$	—
U.S. government treasury securities		—		—		—		—
Total cash equivalents	$	94,394	$	94,394	$	—	$	—
Short-term marketable securities:
U.S. government treasury securities	$	19,928	$	19,928	$	—	$	—
Total marketable securities	$	19,928	$	19,928	$	—	$	—

The Company classifies its money market funds and U.S. government treasury securities as Level 1 assets under the fair value hierarchy as these assets have been valued using quoted market prices in active markets without any valuation adjustment. The Company classifies its derivative liabilities and tranche liability as Level 3 liabilities under the fair value hierarchy as these liabilities have been valued using pricing models with unobservable inputs supported by little or no market activity that are significant to the fair value of the liabilities. The carrying amounts of prepaid expenses and other current assets, accounts payable, accrued expenses and other current liabilities approximate their fair value due to their short-term maturities. During the periods presented, the Company has not changed the manner in which it values liabilities that are measured at estimated fair value using Level 3 inputs. There were no transfers within the hierarchy for any period presented.

The Company issued derivative liabilities embedded in convertible promissory notes and the tranche liability related to the convertible note financing, which are accounted for at fair value on a recurring basis (Note 8).

The Company estimated the fair value of the derivative liabilities embedded in the convertible promissory notes using a with-and-without scenario analysis. The Company estimated that the embedded change of control feature fair values were minimal based on the low probability of the change of control events during the six months ended June 30, 2025.

The following assumptions were used to determine the estimated fair value of the derivative liabilities related to the redemption features as of the issuance dates:


		At Issuance Date (January 10, 2025)
Expected term (in years)		0.2 – 0.3
Probability of achievement		0.0% – 80.0%
Discount rate		8.50%

The following assumptions were used to determine the estimated fair value of the derivative liabilities related to the redemption features as of the issuance date and as of December 31, 2024:


	Issuance Dates	December 31, 2024
Expected term (in years)	0.4 – 1.3	0.2 – 0.4
Probability of achievement	0.0% – 90.0%	0.0% – 80.0%
Discount rate	9.5% – 18.7%	9.0%

As all outstanding convertible promissory notes, other than the AlloVir Note, were converted on March 18, 2025, in connection with the closing of the Merger, the derivative liabilities expired and their fair values were immaterial at the time of conversion.

The fair value of the tranche liability related to the convertible promissory notes issued in October and November 2024 was estimated using the probability weighted model with the following Level 3 input assumptions: the timing of issuing convertible notes and notes conversion, probabilities of conversion scenarios, the estimated fair value of the Company’s shares into which the note was convertible and a discount rate. The significant assumptions were as follows as of December 31, 2024:


		December 31, 2024
Expected term (in years)		0.2 - 0.4
Probability of achievement		0.0% - 80.0%
Discount rate		9.0%

In March 2025, the Company and other noteholders entered into an acknowledgment of conversion and termination agreement to cancel all unfunded tranches and the tranche liability expired unexercised.

The following table provides a roll-forward of the aggregate fair values of the Company’s outstanding Level 3 financial instruments during the six months ended June 30, 2025 (in thousands):


	Derivative liabilities			Tranche liability
Balance as of December 31, 2024	$	1,042		$	365
Initial fair value at issuance		187			—
Change in fair value		(1,229	)		(365	)
Balance as of June 30, 2025	$	—		$	—

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
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Reference 3: http://www.xbrl.org/2003/role/exampleRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2026	Aug. 04, 2026
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2026
Document Fiscal Year Focus	2026
Document Fiscal Period Focus	Q2
Trading Symbol	KLRS
Entity Registrant Name	KALARIS THERAPEUTICS, INC.
Entity Central Index Key	0001754068
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		23,804,981
Security12b Title	Common Stock, $0.0001 par value per share
Security Exchange Name	NASDAQ
Entity File Number	001-39409
Entity Incorporation State Country Code	DE
Entity Tax Identification Number	83-1971007
Entity Address Address Line1	400 Connell Drive, Suite 5500
Entity Address City Or Town	Berkeley Heights
Entity Address State Or Province	NJ
Entity Address Postal Zip Code	07922
City Area Code	650
Local Phone Number	249-2727
Document Quarterly Report	true
Document Transition Report	false

Balance Sheet Components - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid research and development expenses	$ 778	$ 323
Prepaid insurance	509	185
Prepaid taxes	365	211
Prepaid professional and legal costs		30
Other prepaid expenses and other current assets	217	78
Total prepaid expenses and other current assets	$ 1,869	$ 827

Convertible Promissory Notes

6 Months Ended

Jun. 30, 2026

Debt Disclosure [Abstract]

Convertible Promissory Notes

8. Convertible Promissory Notes

Upon the closing of the Merger on March 18, 2025, all convertible promissory notes were converted, and therefore, there are no outstanding convertible promissory notes, derivative liabilities or tranche liability as of June 30, 2026 and December 31, 2025.

2024 Convertible Promissory Note

In March 2024, the Company issued a convertible promissory note to Samsara (the “2024 Note”) for total proceeds of up to $10.0 million. The 2024 Note was payable in two advances at Samsara’s discretion, carried an annual interest rate of 10%, and had an original maturity date of March 2025. In March and May 2024, Samsara advanced to the Company $5.0 million for an aggregate advance of $10.0 million under the 2024 Note. All unpaid interest and principal were due and payable upon request of Samsara on or after maturity, or in the event of default. The Company could not prepay the principal amount and accrued interest at any time before maturity without the consent of Samsara. The outstanding principal amount of the 2024 Note and any unpaid accrued interest would automatically convert upon the Company issuing shares of redeemable preferred stock to investors pursuant to certain qualifying financing events or upon occurrence of change of control events (the “2024 Note Qualified Financing”).

Unless earlier converted or repaid in connection with the 2024 Note Qualified Financing or a change in control on or prior to the maturity date, or at any time at Samsara’s option, Samsara could have elected to convert the 2024 Note and any unpaid accrued interest into the Company’s common stock at a conversion price equal to the Series B-2 Stock conversion price then in effect.

The 2024 Note was issued to Samsara at the estimated fair value of $12.1 million at the issuance date. Since the convertible promissory notes were issued to a related party and considered not at arm’s length, the total premium of $2.1 million, which was the difference between the fair value at the issuance date and the principal amount of the note, was recognized as a loss on issuance of convertible promissory notes – related party in the condensed consolidated statement of operations and comprehensive loss and as additional paid-in-capital in the condensed statement of redeemable convertible preferred stock and stockholders’ equity (deficit) in March and May 2024 when amounts were advanced under the 2024 Note. The Company recognized a $0.2 million loss on issuance of convertible promissory notes to a related party for the six months ended June 30, 2025.

The 2024 Note contained embedded features that provided Samsara the right to receive cash or a variable number of shares upon a change in control or the completion of a capital raising transaction by the Company. These embedded features were required to be bifurcated and accounted for separately as a compound derivative instrument. The embedded features were initially and subsequently measured at fair value, with changes in the fair value recorded as a change in fair value of derivative liabilities – related party in the condensed consolidated statements of operations and comprehensive loss.

The Company recognized a change in the fair value of derivative liability of $0.5 million for the six months ended June 30, 2025. The 2024 Note was converted into shares of common stock, and the derivative liability expired in connection with the closing of the Merger on March 18, 2025.

For the six months ended June 30, 2025, interest expense for the 2024 Note was $0.8 million, including $0.2 million of contractual interest expense and $0.6 million in amortization of debt discount arising from the separation of the derivative instrument. In connection with the closing of the Merger, the $10.0 million aggregate outstanding principal amount and $0.9 million accrued interest of the 2024 Note were converted into 1,757,951 shares of Legacy Kalaris common stock at a conversion price of $6.20 per share.

2024 and 2025 Bridge Notes

In October 2024, the Company entered into a convertible note purchase agreement with Samsara to sell and issue convertible promissory notes for an aggregate principal amount of up to $25.0 million. In November 2024, the Company amended the agreement and other existing preferred stockholders of the Company joined the agreement. In October 2024, the Company issued to Samsara a convertible promissory note with an aggregate principal amount of approximately $9.0 million (the “October 2024 Note”). In November 2024, the Company issued additional notes with an aggregate principal amount of approximately $1.0 million to Samsara and other investors (the “November 2024 Notes”, and together with the October 2024 Note, the “2024 Bridge Notes”). The October and November 2024 issuance of convertible notes is referred to as the “First Tranche Closing”. The Company had the right to draw up to an additional $15.0 million in three subsequent tranche closings of up to a maximum aggregate principal amount of $5.0 million in each such closing (each, the “Subsequent Tranche Closing”). The 2024 Bridge Notes carried an annual interest rate of 8%, and had an original maturity date of May 2025.

Unless earlier converted or repaid in connection with a qualified financing pursuant to the 2024 Bridge Notes or a change in control on or prior to the maturity date, or at any time at Samsara’s option, Samsara could have elected to convert the 2024 Bridge Notes and any unpaid accrued interest into the Company’s common stock at a conversion price equal to the Series B-2 Stock conversion price then in effect (the “2024 Bridge Notes Optional Conversion”).

The Company determined that the investors’ right to receive additional convertible promissory notes at a predetermined conversion price under each of the Subsequent Tranche Closing represented freestanding instruments that should be accounted for separately as liabilities, initially recorded and subsequently remeasured at fair value until their exercise or expiration.

The 2024 Bridge Notes contained embedded features that provided Samsara and other stockholders the right to receive cash or a variable number of shares upon a change in control or the completion of a capital raising transaction by the Company. These embedded features were required to be bifurcated and accounted for separately as a compound derivative instrument. The embedded features were initially and subsequently measured at fair value with changes in the fair value recorded as a change in fair value of derivative liabilities in the condensed consolidated statements of operations and comprehensive loss. The fair value at issuance of the derivative instrument issued with the 2024 Bridge Notes was $1.0 million. The derivative liabilities created a discount on the advances under the 2024 Bridge Notes that were amortized using the effective interest rate method over the term of the respective advance and recorded as a non-cash interest expense. The change in the fair value of derivative liabilities related to the 2024 Bridge Notes was $0.5 million for the six months ended June 30, 2025. The 2024 Bridge Notes were converted into shares of common stock and the derivative liability expired in connection with the closing of the Merger on the Closing Date.

Pursuant to the Merger Agreement, the Company was permitted to enter into a series of financings to fund its operations prior to the closing of the Merger in an amount not to exceed $15.0 million in the aggregate on a to be converted post-money basis, with up to $7.5 million to be provided by AlloVir and up to $7.5 million to be provided by Legacy Kalaris’ stockholders.

In January 2025, the Company amended its 2024 Bridge Notes agreement and changed the amounts of Subsequent Tranche Closings from $5.0 million for each tranche to $3.75 million for the first two tranches and $7.5 million for the third tranche. No other changes were made to the terms of the 2024 Bridge Notes. In January 2025, Samsara and other investors funded an aggregate principal amount of $3.75 million in convertible promissory notes (the “2025 Bridge Notes”). The 2025 Bridge Notes’ terms were similar to the 2024 Bridge Notes' terms. Samsara and other investors agreed that the 2025 Bridge Notes would convert into shares of Series B-2 Stock at a price per share equal to the Company Value Per Share, as defined in the Merger Agreement, at the closing of the Merger.

The 2025 Bridge Notes were issued to Samsara and other existing preferred stockholders of the Company at the estimated fair value of $3.9 million at the issuance dates. The premium of $0.2 million, which was the difference between the fair value at the issuance date and the principal amount of the notes, was recognized as additional paid-in-capital in the condensed consolidated statement of redeemable convertible preferred stock and stockholders’ equity (deficit) at the issuance date. The fair value of the notes at issuance was estimated using the probability weighted settlements scenarios model discounted to present value with the following range of assumptions: expected term of 0.2 - 0.3 years, probabilities of scenario achievement of 20% - 80% and a discount rate of 8.5%. The 2025 Bridge Notes contained embedded features that provided Samsara and other stockholders the right to receive cash or a variable number of shares upon a change in control or the completion of a capital raising transaction by the Company. These

embedded features were required to be bifurcated and accounted for separately as a compound derivative instrument. The embedded features were initially and subsequently measured at fair value, with changes in the fair value recorded as a change in fair value of derivative liabilities in the condensed consolidated statements of operations and comprehensive loss. The fair value at issuance of the derivative instrument issued with the 2025 Bridge Notes was $0.2 million. The derivative liabilities created a discount on the advances under the 2025 Bridge Notes that were amortized using the effective interest rate method over the term of the respective advance and recorded as a non-cash interest expense. The change in the fair value of derivative liabilities related to the 2025 Bridge Notes was $0.2 million for the six months ended June 30, 2025. The 2025 Bridge Notes were converted into shares of Series B-2 Stock and the derivative liability expired in connection with the closing of the Merger on the Closing Date.

The total interest expense for the 2024 Bridge Notes and 2025 Bridge Notes was $0.6 million for six months ended June 30, 2025. For the six months ended June 30, 2025, total interest expense consisted of $0.2 million of contractual interest expense and $0.4 million in amortization of debt discount arising from the separation of the derivative instrument.

In connection with the closing of the Merger, the $10.0 million aggregate outstanding principal amount and $0.3 million accrued interest of the 2024 Bridge Notes converted into 1,660,888 shares of Legacy Kalaris common stock at a conversion price of $6.20 per share. In connection with the closing of the Merger, the $3.75 million aggregate outstanding principal amount and $0.1 million accrued interest of the 2025 Bridge Notes converted into 794,499 shares of Series B-2 Stock at a price of $4.7851 per share, which then converted on a one-for-one basis into shares of Legacy Kalaris common stock, and subsequently into 160,165 shares of AlloVir common stock.

In March 2025, the Company and other noteholders entered into an acknowledgment of conversion and termination agreement to cancel all unfunded tranches included in the 2024 Bridge Notes. The Company recognized a gain of $0.4 million in the change in fair value of the tranche liability for the six months ended June 30, 2025.

January 2025 AlloVir Convertible Promissory Note

In January 2025, the Company issued the AlloVir Note under which AlloVir funded a principal amount of $3.75 million. At the closing of the Merger on March 18, 2025, the AlloVir Note was cancelled in accordance with its terms.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1C

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 1C
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1C

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1C

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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-Section 50
-Paragraph 1I
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

+ Details

Significant Agreements - Additional Information (Details) - USD ($)	1 Months Ended			3 Months Ended		6 Months Ended		24 Months Ended	63 Months Ended
	Jul. 31, 2024	Mar. 31, 2022	Apr. 30, 2021	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2026	Dec. 31, 2025	Jun. 30, 2022
Significant Agreements [Line Items]
Common stock, shares issued				23,804,981		23,804,981		23,804,981	23,804,981	22,902,418
Accrued expenses and other current liabilities				$ 7,267,000		$ 7,267,000		$ 7,267,000	$ 7,267,000	$ 8,117,000
Research and development expenses				9,018,000	$ 8,440,000	16,590,000	$ 14,470,000
University of California, San Diego \| License Agreement
Significant Agreements [Line Items]
License agreement payment			$ 200,000
Percentage of common stock issued			5.00%
Potential gross proceeds from sale of equity securities			$ 5,000,000
Common stock, shares issued											137,234
Reimbursement of patent costs incurred			100,000				100,000
License maintenance payments for first four anniversaries			10,000
License maintenance payments for fifth and subsequent anniversary			$ 15,000
Sublicense fee percentage within one year			50.00%
Sublicense fee percentage after first dose			10.00%
Minimum percentage of voting stock			50.00%
Agreement termination written notice period			60 days
Initial cash consideration			$ 200,000
Research and development expenses			$ 200,000	0	$ 0	0	$ 0		100,000
Derivative liability fair value assignment fee				0		0		0	0	0
University of California, San Diego \| License Agreement \| Common Stock
Significant Agreements [Line Items]
Common stock, shares issued		81,794	55,440
Issuance of shares		$ 200,000	$ 100,000
University of California, San Diego \| License Agreement \| Minimum
Significant Agreements [Line Items]
One-time cash milestone payment upon event of liquidity			100,000
University of California, San Diego \| License Agreement \| Maximum
Significant Agreements [Line Items]
One-time cash milestone payment upon event of liquidity			1,000,000
Potential milestone payment upon achievement of development and regulatory milestones			$ 4,600,000
Samsara
Significant Agreements [Line Items]
Accrued expenses and other current liabilities				$ 50,000.00		$ 50,000.00		50,000.00	$ 50,000.00	$ 100,000
Samsara \| Royalty Agreement
Significant Agreements [Line Items]
Research and development expenses	$ 32,000,000
Royalty expiration period	10 years
Future royalty payment liability	$ 32,100,000
Percentage of discount rate	25.00%
Interest expense for royalty liability								$ 0
Samsara \| Royalty Agreement \| Common Stock
Significant Agreements [Line Items]
Redemption of common stock issued	10,080
Repurchase of common shares, value	$ 32,000

Stockholders' Equity (Deficit)

6 Months Ended

Jun. 30, 2026

Equity [Abstract]

Stockholders' Equity (Deficit)

12. Stockholders’ Equity (Deficit)

As of June 30, 2026 and December 31, 2025, the Company’s certificate of incorporation authorized the Company to issue 300,000,000 shares of common stock, par value $0.0001 per share, and 10,000,000 shares of preferred stock, par value $0.0001 per share. There were no shares of preferred stock issued or outstanding as of June 30, 2026 and December 31, 2025. The voting, dividend and liquidation rights of the holders of the Company’s common stock are subject to and qualified by the rights, powers and preferences of the holders of preferred stock.

The holders of the Company’s common stock are entitled to one vote for each share of common stock held on all matters submitted to a vote of the stockholders, and the holders of our common stock do not have any cumulative voting rights. The number of authorized shares of common stock may from time to time be increased or decreased (but not below the number of shares of such class outstanding) by the affirmative vote of the holders of a majority in voting power of the outstanding shares of capital stock of the Company.

2025 Private Placement

On December 17, 2025, the Company entered into a Securities Purchase Agreement (the “2025 Securities Purchase Agreement”) with certain institutional investors (the “PIPE Investors”) named therein. Pursuant to the 2025 Securities Purchase Agreement, the Company issued and sold to the PIPE Investors in a private placement (the “2025 Private Placement”) an aggregate of (i) 4,200,000 shares of the Company’s common stock at a purchase price of $10.00 per share, for aggregate gross proceeds of $42.0 million, and (ii) pre-funded warrants (“Pre-Funded Warrants”) to purchase up to an aggregate of 800,000 shares of the Company’s common stock at a purchase price of $9.9999 per Pre-Funded Warrant, which represents the per share purchase price of the Company’s common stock less the $0.0001 per share exercise price for each Pre-Funded Warrant, for total aggregate proceeds of $8.0 million. The Pre-Funded Warrants are exercisable at any time after the date of issuance and will be exercisable until the Pre-Funded Warrant is exercised in full. The 2025 Private Placement closed on December 22, 2025, for aggregate gross proceeds of $50.0 million, before deducting placement agent fees and offering expenses of $3.4 million, for net proceeds of $46.6 million.

Under the terms of the Pre-Funded Warrants, the Company may not effect the exercise of any portion of such Pre-Funded Warrant, and a holder will not be entitled to exercise any portion of such Pre-Funded Warrant, if, upon giving effect to such exercise, the holder, together with its affiliates, would beneficially own more than 4.99% or 9.99%, at the option of the holder, of the number of shares of common stock outstanding immediately after giving effect to such exercise. The holders of Pre-Funded Warrants may increase or decrease such percentage by providing at least 61 days’ prior notice to the Company, provided that such percentage may in no event exceed 19.99%. The Pre-Funded Warrants are indexed to the Company's common stock and none of the provisions of the warrant would require a cash settlement. Therefore, the Pre-Funded Warrants were classified as a component of equity in the Company’s consolidated balance sheet upon entering into the 2025 Securities Purchase Agreement as they were freestanding financial instruments that were immediately exercisable, did not embody an obligation for the Company to repurchase its own shares and entitled the holder to receive a fixed number of shares of common stock upon exercise. On April 13, 2026, all of the Pre-Funded Warrants were exercised on a cashless basis, resulting in the issuance of 799,987 shares of the Company’s common stock. As of June 30, 2026, no Pre-Funded Warrants remained outstanding.

At-the-Market Offering

On April 3, 2026, the Company filed a shelf registration statement on Form S-3 with the SEC, which was declared effective on April 13, 2026 (the “Shelf Registration Statement”). Under the Shelf Registration Statement, the Company may offer and sell up to $350.0 million of a variety of securities including common stock, preferred stock, debt securities, subscription rights, warrants or units during the three-year period that commenced upon the Shelf Registration becoming effective. In connection with the filing of the Shelf Registration Statement, the Company entered into a Common Stock Sales Agreement (the “Sales Agreement”) with TD Securities (USA) LLC (“TD Cowen”), pursuant to which the Company may issue and sell, from time to time, up to an aggregate of $100.0 million of its common stock in an at-the-market equity offering through TD Cowen, as sales agent (the “At-the-Market Offering”). TD Cowen is entitled to receive compensation equal to up to 3.0% of the gross sales price of the shares of common stock sold pursuant to the Sales Agreement.

As of June 30, 2026, the Company had not sold any shares of its common stock pursuant to the At-the-Market Offering. As of June 30, 2026, the Company had capitalized $0.5 million of deferred transaction costs related to the At-the-Market Offering, which are included in current assets on the consolidated balance sheets. The capitalized deferred transaction costs will be reclassified to additional paid-in capital as a reduction of the gross proceeds received upon the sale of common stock under the At-the-Market Offering on a pro-rata basis. Compensation paid to TD Cowen will similarly be recorded as a reduction of additional paid-in capital in the period the related shares are issued and sold. Any deferred costs remaining at the termination or expiration of the Sales Agreement will be charged to expense at that time. Costs incurred to maintain the At-the-Market Offering will be expensed as incurred.

Common Stock

As of June 30, 2026 and December 31, 2025, shares of common stock reserved for future issuance were as follows:


	June 30,		December 31,
	2026		2025
Outstanding stock option awards		2,535,975		2,142,278
Pre-funded warrants to purchase common stock		—		800,000
Shares available for future options grants under the Equity Plans		1,959,250		1,310,403
Shares available for grant under the 2020 ESPP		172,487		119,326
Total shares reserved for future issuance		4,667,712		4,372,007

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-8A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478448/946-505-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480237/815-40-50-6

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
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-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-16

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

+ Details

Merger with AlloVir - Schedule of Number of Shares Common Stock Issued and Outstanding (Details) - Common Stock - AlloVir	Mar. 18, 2025 shares
Business Combination, Consideration Transferred, Equity Interest [Line Items]
AlloVir's common stock outstanding	5,043,652
AlloVir's restricted stock units accelerated and settled in common stock	24,022
Common stock issued to Legacy Kalaris' securityholders at the Effective Time	13,634,744
Total	18,702,418

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value On Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Cash equivalents:
Cash equivalents	$ 41,696	$ 94,394
Short-term marketable securities:
Marketable securities	50,365	19,928
Total marketable securities	92,061
Money Market Funds
Cash equivalents:
Cash equivalents	41,696	94,394
U.S. Government Treasury Securities
Short-term marketable securities:
Short-term marketable securities	50,365	19,928
Level 1
Cash equivalents:
Cash equivalents	41,696	94,394
Short-term marketable securities:
Marketable securities		19,928
Total marketable securities	92,061
Level 1 \| Money Market Funds
Cash equivalents:
Cash equivalents	41,696	94,394
Level 1 \| U.S. Government Treasury Securities
Short-term marketable securities:
Short-term marketable securities	$ 50,365	$ 19,928

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

+ Details

Leases

6 Months Ended

Jun. 30, 2026

Leases [Abstract]

Leases

9. Leases

In February 2025, the Company entered into an operating lease agreement for office space in Berkeley Heights, New Jersey. In accordance with ASC 842, Leases (“ASC 842”) the Company has determined the lease commencement occurred in September 2025 upon substantial completion of lessor-owned improvements. The lease is expected to terminate in December 2031, however, the Company has the option to extend the lease term twice for an additional three years. As of June 30, 2026, it is not reasonably certain that the Company will exercise this option to extend. The Company can terminate the lease after four years and four months after the lease commencement date with a termination penalty of $0.3 million. In addition to the base rent, the Company will pay its share of operating expenses and taxes. The lessor provided a tenant improvement allowance of up to $0.4 million, which the Company fully utilized. The Company is responsible for additional improvement expense incurred in excess of the tenant improvement allowance and has incurred $0.1 million of excess costs as of June 30, 2026. The Company records excess costs as payments in the measurement of lease liabilities.

In connection with the signing of the lease, the Company secured a letter of credit in favor of the lessor in the amount of $0.5 million, which will be reduced to $0.2 million over five years. The letter of credit is recorded as restricted cash in the condensed consolidated balance sheet as of June 30, 2026.

The following table summarizes the presentation of the Company’s operating lease on its condensed consolidated balance sheet as of June 30, 2026 (in thousands):


Leases	Balance sheet classification	June 30, 2026
Assets:
Operating lease assets	Operating lease right-of-use assets	$	1,389
Total lease assets		$	1,389
Liabilities:
Current:
Operating lease liabilities	Operating lease liability, current	$	347
Noncurrent:
Operating lease liabilities	Operating lease liability, long-term		1,053
Total lease liabilities		$	1,400

The components of lease cost under ASC 842 included within general and administrative expenses in the Company’s condensed consolidated statements of operations and comprehensive loss were as follows for the three and six months ended June 30, 2026 (in thousands):


Lease cost	Three Months Ended June 30, 2026		Six Months Ended June 30, 2026
Operating lease cost	$	88	$	176
Variable lease cost		7		15
Total lease cost	$	95	$	191

As of June 30, 2026, the weighted-average remaining lease term for the operating lease was 5.5 years, and the weighted-average discount rate was 13.12%. Cash paid for amounts included in the measurement of lease liabilities was $0.1 million for the six months ended June 30, 2026.

Future minimum annual lease commitments under the Company's non-cancelable operating lease as of June 30, 2026 was as follows (in thousands):


Year ended December 31,	Amount
2026 (remaining 6 months)	$	196
2027		342
2028		349
2029		356
2030		363
Thereafter		337
Total lease payments		1,943
Less: interest		(543	)
Present value of operating lease liabilities	$	1,400

Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2026

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost and Estimated Fair Value of Marketable Securities

The following table summarizes the amortized cost and estimated fair value of the Company’s U.S. government treasury securities, which are considered to be available-for-sale marketable securities and are included in marketable securities on the condensed consolidated balance sheet as of June 30, 2026 and December 31, 2025 (in thousands):


	June 30, 2026
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Short-term marketable securities:
U.S. government treasury securities	$	50,438	$	—	$	(73	)	$	50,365
Total marketable securities	$	50,438	$	—	$	(73	)	$	50,365


	December 31, 2025
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Short-term marketable securities:
U.S. government treasury securities	$	19,922	$	6	$	—	$	19,928
Total short-term marketable securities	$	19,922	$	6	$	—	$	19,928

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
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-Section 50
-Paragraph 2
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

+ Details

Nature of the Business

6 Months Ended

Jun. 30, 2026

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Nature of the Business

1. Nature of the Business

Description of the Business

Kalaris Therapeutics, Inc. (“Kalaris” or “the Company”) is a clinical stage biopharmaceutical company dedicated to the development and commercialization of treatments for prevalent retinal diseases with major unmet medical needs. The Company is developing TH103, a novel, clinical stage anti-vascular endothelial growth factor (“VEGF”) drug, specifically engineered to achieve extended intraocular retention with enhanced VEGF inhibition in patients with exudative and/or neovascular retinal diseases.

On March 18, 2025 (the “Closing Date”), AlloVir, Inc., a Delaware corporation (“AlloVir”), consummated the previously announced merger (the “Merger”) pursuant to the terms of the Agreement and Plan of Merger, dated as of November 7, 2024 (the “Merger Agreement”), by and among AlloVir, Aurora Merger Sub, Inc., a Delaware corporation and wholly-owned subsidiary of AlloVir (“Merger Sub”) and Kalaris Tx, Inc. (formerly Kalaris Therapeutics, Inc.), a Delaware corporation (“Legacy Kalaris”). At the effective time of the Merger (the “Effective Time”), Merger Sub merged with and into Legacy Kalaris, with Legacy Kalaris continuing as a wholly-owned subsidiary of AlloVir and the surviving corporation of the Merger and, after giving effect to the Merger, Legacy Kalaris became a wholly-owned subsidiary of AlloVir. Immediately following the Effective Time, AlloVir changed its name to “Kalaris Therapeutics, Inc.” At the Effective Time, the Company’s business became primarily the business conducted by Legacy Kalaris. The Company's common stock, which was previously listed on The Nasdaq Capital Market and traded under the ticker symbol “ALVR” through the close of business on the Closing Date, commenced trading on The Nasdaq Global Market under the ticker symbol “KLRS” on March 19, 2025. Refer to Note 3, “Merger with AlloVir”, for further details of the Merger.

Samsara BioCapital L.P. and its affiliates (collectively, “Samsara”), the Company's majority stockholder and a related party, have provided Legacy Kalaris with significant equity and debt financing since its inception, and management and operational support services to the Company. Refer to Note 15 for further details of the related party transactions with Samsara.

Liquidity

The Company has incurred significant losses and negative cash flows from operations since its inception. During the six months ended June 30, 2026 and 2025, the Company incurred net losses of $22.4 million and $21.5 million, respectively. During the six months ended June 30, 2026 and 2025, the Company had negative cash flows from operations of $22.6 million and $20.0 million, respectively. As of June 30, 2026 and December 31, 2025, the Company had an accumulated deficit of $182.4 million and $160.0 million, respectively. The Company expects to continue to incur substantial losses for the foreseeable future, and its ability to achieve and sustain profitability will depend on the successful development, approval, and commercialization of product candidates and on the achievement of sufficient revenues to support the Company’s operations.

Since its inception, the Company has funded its operations primarily with proceeds from sales of its redeemable convertible preferred stock, issuances of convertible promissory notes and a simple agreement for future equity (“SAFE”), from cash and cash equivalents of AlloVir received in the Merger, and with proceeds from the 2025 Private Placement (as defined below). Refer to Note 12 for further details of the 2025 Private Placement.

As of June 30, 2026, the Company had cash, cash equivalents and marketable securities of $93.5 million. The Company expects that the existing cash, cash equivalents and marketable securities will be sufficient to fund its operating expenses and capital expenditure requirements for at least twelve months from the issuance date of these condensed consolidated financial statements.

The Company will need to raise additional financing to continue its product's development for the foreseeable future until it becomes profitable. The Company plans to monitor expenses and raise additional capital through a combination of equity and debt financings, strategic alliances, and licensing arrangements. The Company’s ability to access capital when needed is not assured and, if capital is not available to the Company when, and in the amounts needed, the Company may be required to significantly curtail, delay or discontinue one or more of its research or development programs or the commercialization of any product candidate, or be unable to expand its operations or otherwise capitalize on the Company’s business opportunities, as desired, which could materially harm the Company’s business, financial condition and results of operations.

Net Loss Per Share Attributable to Common Stockholders - Additional Information (Details) - $ / shares		6 Months Ended
	Apr. 13, 2026	Jun. 30, 2026
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Issuance of common stock upon exercise of pre-funded warrants, Shares	799,987
Pre Funded Warrant [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Warrants to purchase common stock		800,000
Purchase price		$ 9.9999
Warrants outstanding		0
Warrants exercised date		Apr. 13, 2026

Leases - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	6 Months Ended
	Feb. 28, 2025	Jun. 30, 2026
Leases [Abstract]
LeaseTerminate Month and Year	2031-12
Lease extend term description		the Company has the option to extend the lease term twice for an additional three years. As of June 30, 2026, it is not reasonably certain that the Company will exercise this option to extend.
Lessee, operating lease, renewal term	3 years
Operating lease, option to terminate description		can terminate the lease after four years and four months after the lease commencement date with a termination penalty of $0.3 million.
Termination penalty	$ 0.3
Maximum lease tenant improvement allowance	0.4
Tenant improvement allowance		$ 0.1
Letter of credit in favor of lessor	0.5
Reduction in letter of credit	$ 0.2
Weighted-average remaining lease term		5 years 6 months
Weighted-average discount rate		13.12%
Cash payments for measurement of lease liabilities		$ 0.1

Related Parties - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Related Party Transaction [Line Items]
General and administrative expenses	$ 3,368	$ 3,816	$ 7,629	$ 8,140
Accrued expenses and other current liabilities	7,267		7,267		$ 8,117
Royalty obligation - related party	32,076		32,076		32,076
Consulting fees	20		$ 30
Samsara
Related Party Transaction [Line Items]
Business services agreement term			5 years
Business services agreement terminated period			15 days
General and administrative expenses	100	40	$ 200	200
In-kind services	0	$ 0	0	$ 0
Accrued expenses and other current liabilities	50		50		100
Royalty obligation - related party	$ 32,100		$ 32,100		$ 32,100

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Leases - Schedule of Components of Lease Cost (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2026	Jun. 30, 2026
Leases [Abstract]
Operating lease cost	$ 88	$ 176
Variable lease cost	7	15
Total lease cost	$ 95	$ 191

Leases - Schedule of Future Minimum Annual Lease Commitments under Non-cancellable Operating Leases (Details) $ in Thousands	Jun. 30, 2026 USD ($)
Leases [Abstract]
2026 (remaining 6 months)	$ 196
2027	342
2028	349
2029	356
2030	363
Thereafter	337
Total lease payments	1,943
Less: interest	(543)
Present value of operating lease liabilities	$ 1,400

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Current assets:
Cash and cash equivalents	$ 43,173	$ 98,054
Short-term marketable securities	50,365	19,928
Deferred transaction costs	514	0
Prepaid expenses and other current assets	1,869	827
Total current assets	95,921	118,809
Operating lease right-of-use assets	1,389	1,475
Restricted cash	500	499
Other non-current assets	1,729	953
Total assets	99,539	121,736
Current liabilities:
Accounts payable	1,124	1,281
Accrued expenses and other current liabilities (including $40 and $67 due to a related party)	7,267	8,117
Operating lease liabilities, current	347	316
Total current liabilities	8,738	9,714
Royalty obligation - related party	32,076	32,076
Operating lease liabilities, long-term	1,053	1,132
Total liabilities	41,867	42,922
Commitments and contingencies (Note 9)
Stockholders' equity:
Common stock, $0.0001 and $0.0001 par value as of June 30, 2026 and December 31, 2025, respectively; 300,000,000 shares authorized as of June 30, 2026 and December 31, 2025; 23,804,981 and 22,902,418 shares issued and outstanding as of June 30, 2026 and December 31, 2025, respectively	2	2
Additional paid-in capital	240,113	238,805
Accumulated other comprehensive income (loss)	(73)	6
Accumulated deficit	(182,370)	(159,999)
Total stockholders' equity	57,672	78,814
Total liabilities and stockholders' equity	$ 99,539	$ 121,736

Stockholders' Equity (Deficit) - Additional Information (Details) - USD ($)				3 Months Ended	6 Months Ended
	Apr. 13, 2026	Dec. 22, 2025	Dec. 17, 2025	Jun. 30, 2026	Jun. 30, 2026	Dec. 31, 2025
Subsidiary, Sale of Stock [Line Items]
Common stock, shares authorized				300,000,000	300,000,000	300,000,000
Common stock, par value				$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares authorized				10,000,000	10,000,000	10,000,000
Preferred stock outstanding				0	0	0
Preferred stock issued				0	0	0
Preferred stock, par or stated value per share				$ 0.0001	$ 0.0001	$ 0.0001
Issuance of common stock upon exercise of pre-funded warrants, Shares	799,987
Deferred transaction costs				$ 514,000	$ 514,000	$ 0
Securities Purchase Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Net proceeds from issuance of private placement		$ 46,600,000
Issuance costs		3,400,000
Pre-Funded Warrants
Subsidiary, Sale of Stock [Line Items]
Pre-Funded Warrant Notice Period			61 days
Warrants exercised date					Apr. 13, 2026
Warrants outstanding				0	0
Pre-Funded Warrants \| Securities Purchase Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock shares issued			800,000
Purchase price per share			$ 9.9999
Exercise Price per Share			$ 0.0001
Net proceeds from issuance of private placement			$ 8,000,000
Private Placement [Member] \| Securities Purchase Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock shares issued			4,200,000
Purchase price per share			$ 10
Aggregate gross proceeds of common stock			$ 42,000,000
December Two Thousand Twenty Five Private Placement [Member]
Subsidiary, Sale of Stock [Line Items]
Aggregate gross proceeds of common stock		$ 50,000,000
Maximum \| At-the-Market Offering
Subsidiary, Sale of Stock [Line Items]
Sale of securities, offering price	$ 350,000,000
Common Stock
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock upon exercise of pre-funded warrants, Shares				799,987
Common Stock \| Pre-Funded Warrants
Subsidiary, Sale of Stock [Line Items]
Shares outstanding percentage			19.99%
Common Stock \| At-the-Market Offering
Subsidiary, Sale of Stock [Line Items]
Common stock shares issued					0
Aggregate compensation payable percentage	3.00%
Sale of stock, effective Date	Apr. 13, 2026
Deferred transaction costs				$ 500,000	$ 500,000
Common Stock \| Minimum \| Pre-Funded Warrants
Subsidiary, Sale of Stock [Line Items]
Shares outstanding percentage			4.99%
Common Stock \| Maximum \| Pre-Funded Warrants
Subsidiary, Sale of Stock [Line Items]
Shares outstanding percentage			9.99%
Common Stock \| Maximum \| At-the-Market Offering
Subsidiary, Sale of Stock [Line Items]
Sale of stock, offering price	$ 100,000,000

Segment Reporting - Summary of Segment Loss (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2026	Mar. 31, 2026	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2026	Jun. 30, 2025
Segment Reporting [Abstract]
CDMO, CRO and other third-party clinical trials and consulting costs	$ 7,395		$ 6,915		$ 13,608	$ 11,727
Internal research and development personnel costs	1,496		1,175		2,770	2,244
Other research and development costs	127		350		212	499
General and administrative personnel expenses	1,220		1,094		2,785	1,771
Other general and administrative expenses	2,148		2,722		4,844	6,369
Interest expense	0		0		0	1,443
Other segment items	(871)		(906)		(1,848)	(2,507)
Net loss	$ (11,515)	$ (10,856)	$ (11,350)	$ (10,196)	$ (22,371)	$ (21,546)

- Definition

Amount of interest expense classified as operating and nonoperating. Includes, but is not limited to, cost of borrowing accounted for as interest expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (d)
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
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Reference 3: http://www.xbrl.org/2003/role/exampleRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/1943274/2147479105/946-220-45-3

+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Operating expenses:
Research and development (including $15, $12, $30 and $25 for a related party)	$ 9,018	$ 8,440	$ 16,590	$ 14,470
General and administrative (including $93, $37, $160 and $188 for a related party)	3,368	3,816	7,629	8,140
Total operating expenses	12,386	12,256	24,219	22,610
Loss from operations	(12,386)	(12,256)	(24,219)	(22,610)
Other income (expense), net:
Change in fair value of tranche liability (including $0, $0, $0 and $331 for a related party)	0	0	0	365
Change in fair value of derivative liabilities (including $0, $0, $0 and $1,165 for a related party)	0	0	0	1,229
Interest expense (including $0, $0, $0 and $1,384 for a related party)	0	0	0	(1,443)
Loss on extinguishment and on issuance of convertible promissory notes (including $0, $0, $0 and $169 for a related party)	0	0	0	(186)
Other income, net	871	906	1,848	1,099
Total other income, net	871	906	1,848	1,064
Net loss	$ (11,515)	$ (11,350)	$ (22,371)	$ (21,546)
Net loss per share attributable to common stockholders - basic	$ (0.48)	$ (0.61)	$ (0.94)	$ (1.89)
Net loss per share attributable to common stockholders - diluted	$ (0.48)	$ (0.61)	$ (0.94)	$ (1.89)
Weighted-average shares outstanding - basic	23,797,306	18,701,286	23,760,665	11,417,677
Weighted-average shares outstanding - diluted	23,797,306	18,701,286	23,760,665	11,417,677
Comprehensive loss:
Net loss	$ (11,515)	$ (11,350)	$ (22,371)	$ (21,546)
Other comprehensive loss:
Unrealized loss on marketable securities, net of tax	(24)	0	(79)	0
Total other comprehensive loss	(24)	0	(79)	0
Comprehensive loss	$ (11,539)	$ (11,350)	$ (22,450)	$ (21,546)

Marketable Securities

6 Months Ended

Jun. 30, 2026

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

4. Marketable Securities


	June 30, 2026
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Short-term marketable securities:
U.S. government treasury securities	$	50,438	$	—	$	(73	)	$	50,365
Total marketable securities	$	50,438	$	—	$	(73	)	$	50,365


	December 31, 2025
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Short-term marketable securities:
U.S. government treasury securities	$	19,922	$	6	$	—	$	19,928
Total short-term marketable securities	$	19,922	$	6	$	—	$	19,928

Certain short-term debt securities with original maturities of less than three months are included in cash and cash equivalents on the condensed consolidated balance sheets and are not included in the tables above. As of June 30, 2026, and December 31, 2025, all marketable securities had contractual maturities within one year. There were no available-for-sale securities in a continuous unrealized loss position for greater than 12 months.

The Company holds debt securities with high credit quality and has determined that there was no material change in the credit risk of any of its debt securities. The total fair value of marketable securities as of June 30, 2026 was $50.4 million.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2026

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). AlloVir and its subsidiaries’ operating results are included in the Company’s condensed consolidated financial statements from the Closing Date of the Merger. All other accompanying financial data as of December 31, 2025, and for the three and six months ended June 30, 2025, include only the accounts and disclosures of Legacy Kalaris. All intercompany transactions and balances have been eliminated upon consolidation.

These unaudited condensed consolidated financial statements and the notes accompanying them should be read in conjunction with Legacy Kalaris' audited financial statements as of and for the year ended December 31, 2025, included in the Company’s Annual Report on Form 10-K filed with the SEC on March 17, 2026.

All historical common share data and per-share amounts prior to the Merger were retrospectively recast to reflect the effect of the exchange ratio of 0.2016 per one share, which was determined in accordance with the Merger Agreement. The number of authorized shares and par value per share were not recast. The conversion ratios for each series of redeemable convertible preferred stock, which were converted into shares of common stock in connection with the closing of the Merger, were proportionally recast.

Unaudited Condensed Financial Statements

The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair statement of the Company’s financial position as of June 30, 2026 and its results of operations and its cash flows for the three and six months ended June 30, 2026 and 2025. The results of operations for the three and six months ended June 30, 2026 and 2025 are not necessarily indicative of the results to be expected for the year ending December 31, 2026, or for any other future annual or interim period. The consolidated balance sheet as of December 31, 2025 included herein was derived from the audited financial statements as of that date. Certain information and footnote disclosures normally included in consolidated financial statements prepared in accordance with GAAP have been condensed or omitted from these unaudited condensed consolidated financial statements.

Marketable Securities

The Company classifies all investments with a remaining maturity of less than one year as short-term marketable securities and investments with a remaining maturity of greater than one year as long-term marketable securities. Marketable securities consist of U.S. treasury securities classified as available-for-sale. The Company's marketable securities are classified as available-for-sale as they are available to fund current operations, even if the Company intends to hold the marketable securities to maturity. Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in other comprehensive income (loss) until realized. The amortized cost of debt securities in this category is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization or accretion is included in other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. Realized gains and losses are determined using the specific identification method and are included in other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. Interest on available-for-sale securities is included in other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. The Company reviews its portfolio of marketable securities, using both quantitative and qualitative factors, to determine if declines in fair value below cost have resulted from a credit-related loss. If the decline in fair value is due to credit-related factors, a loss is recognized in other income (expense).

Recently Issued Accounting Pronouncements Not Yet Adopted

ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40)

In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses to improve financial reporting by requiring that public business entities disclose additional information about specific expense categories in the notes to financial statements at interim and annual reporting periods. The amendments in this ASU do not change or remove current expense disclosure requirements; however, the amendments affect where such information appears in the notes to the financial statements because entities are required to include certain current disclosures in the same tabular format as the other disaggregation requirements in the amendments. This ASU is effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods

beginning after December 15, 2027. Early adoption is permitted. The Company is currently evaluating the impact that the updated standard will have on its consolidated financial statement disclosures and financial reporting processes.

ASU 2025-06, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40)

In September 2025, the FASB issued ASU 2025-06, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software to modernize the accounting for software costs and increase the operability of the recognition guidance considering different methods of software development. The amendments are effective for annual reporting periods beginning after December 15, 2027, and interim reporting periods within those annual reporting periods. Early adoption is permitted as of the beginning of an annual reporting period. The Company is currently evaluating the impact that the updated standard will have on its consolidated financial statement disclosures.

Redeemable Convertible Preferred Stock

6 Months Ended

Jun. 30, 2026

Temporary Equity Disclosure [Abstract]

Redeemable Convertible Preferred Stock

11. Redeemable Convertible Preferred Stock

In January 2024, the Company issued 1,280,000 shares of Series B-2 Stock at a price of $1.25 per share for gross cash proceeds of $1.6 million.

Upon the closing of the Merger on March 18, 2025, all outstanding shares of redeemable convertible preferred stock were automatically converted into shares of common stock and no redeemable convertible preferred stock was outstanding as of June 30, 2026 and December 31, 2025.

Stock-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Share-Based Payment Arrangement [Abstract]
Number of Shares, Options outstanding, Beginning Balance	2,142,278
Number of Shares, Options granted	892,420
Number of Shares, Options exercised	(102,576)	0
Number of Shares, Options cancelled	(396,147)
Number of Shares, Options outstanding, Ending Balance	2,535,975		2,142,278
Number of Shares, Exercisable	849,138
Number of Shares, Vested and expected to vest, June 30, 2026	2,535,975
Weighted Average Exercise Price Per Share, Options outstanding, Beginning Balance	$ 3.98
Weighted Average Exercise Price Per Share, Options granted	6.61
Weighted Average Exercise Price Per Share, Options Exercised	0.84
Weighted Average Exercise Price Per Share, Options cancelled	5.05
Weighted Average Exercise Price Per Share, Options outstanding, Ending Balance	4.87		$ 3.98
Weighted Average Exercise Price Per Share, Options Exercisable	3.07
Weighted Average Exercise Price Per Share, Options Vested and expected to vest, June 30, 2026	$ 4.87
Weighted Average Remaining Contractual Term (in years), Options outstanding	8 years 8 months 26 days		8 years 10 months 17 days
Weighted Average Remaining Contractual Term (in years), Exercisable	8 years
Weighted Average Remaining Contractual Term (in years), Vested and expected to vest, June 30, 2026	8 years 8 months 26 days
Aggregate Intrinsic Value, Options outstanding, Beginning Balance	$ 9,552
Aggregate Intrinsic Value, Options Exercised	581	$ 600
Aggregate Intrinsic Value, Options outstanding, Ending Balance	2,666		$ 9,552
Aggregate Intrinsic Value, Exercisable	1,780
Aggregate Intrinsic Value, Vested and expected to vest, June 30, 2026	$ 2,666

Segment Reporting (Tables)

6 Months Ended

Jun. 30, 2026

Segment Reporting [Abstract]

Summary of Segment Loss

The following is the Company’s summary of segment loss, including significant segment expenses for the three and six months ended June 30, 2026 and 2025 (in thousands):


	Three Months Ended June 30,						Six Months Ended June 30,
	2026			2025			2026			2025
External research and development expenses:
CDMO, CRO and other third-party clinical trials and consulting costs	$	7,395		$	6,915		$	13,608		$	11,727
Internal research and development personnel costs		1,496			1,175			2,770			2,244
Other research and development costs		127			350			212			499
General and administrative personnel expenses		1,220			1,094			2,785			1,771
Other general and administrative expenses		2,148			2,722			4,844			6,369
Interest expense		—			—			—			1,443
Other segment items1		(871	)		(906	)		(1,848	)		(2,507	)
Net loss	$	(11,515	)	$	(11,350	)	$	(22,371	)	$	(21,546	)

1 Other segment items include change in fair value of tranche liability, change in fair value of derivative liabilities, loss on extinguishment and on issuance of convertible promissory notes and other income, net.

Leases (Tables)

6 Months Ended

Jun. 30, 2026

Leases [Abstract]

Schedule of Operating Lease on Its Consolidated Balance Sheet

The following table summarizes the presentation of the Company’s operating lease on its condensed consolidated balance sheet as of June 30, 2026 (in thousands):


Leases	Balance sheet classification	June 30, 2026
Assets:
Operating lease assets	Operating lease right-of-use assets	$	1,389
Total lease assets		$	1,389
Liabilities:
Current:
Operating lease liabilities	Operating lease liability, current	$	347
Noncurrent:
Operating lease liabilities	Operating lease liability, long-term		1,053
Total lease liabilities		$	1,400

Schedule of Components of Lease Cost


Lease cost	Three Months Ended June 30, 2026		Six Months Ended June 30, 2026
Operating lease cost	$	88	$	176
Variable lease cost		7		15
Total lease cost	$	95	$	191

Schedule of Future Minimum Annual Lease Commitments under Non-cancellable Operating Leases

Future minimum annual lease commitments under the Company's non-cancelable operating lease as of June 30, 2026 was as follows (in thousands):


Year ended December 31,	Amount
2026 (remaining 6 months)	$	196
2027		342
2028		349
2029		356
2030		363
Thereafter		337
Total lease payments		1,943
Less: interest		(543	)
Present value of operating lease liabilities	$	1,400

Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended
	Feb. 28, 2022	Jul. 31, 2020	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting percentage					10.00%
Estimated fair market value of underlying common stock					110.00%
Term of contract					5 years
Reserved shares of common stock for issuance			4,667,712		4,667,712		4,372,007
Number of Shares, Options exercised					102,576	0
Weighted-average fair value of options exercised per share					$ 2.9	$ 2.9
Aggregate Intrinsic Value, Options Exercised					$ 581,000	$ 600,000
Number of Shares, Options granted					892,420
Stock issued under employee stock purchase plan			0		0
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for issuance			2,535,975		2,535,975		2,142,278
Total fair value of options vested					$ 1,700,000	$ 500,000
Number of Shares, Options granted				0
Unrecognized stock-based compensation expenses			$ 8,100,000		$ 8,100,000
Weighted average period of cost expected to be recognized					2 years 10 months 24 days
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted Stock Awards, granted			0	0	0	0
Restricted Stock Awards, repurchased			0	0	0	0
2019 Stock Option and Grant Plan \| Stock Available For Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for issuance			1,588,703		1,588,703
Shares available for future grants			434,158		434,158
2019 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Offering price per share	$ 0.005
2019 Plan \| Former President
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of restricted stock awards	203,670
2019 Plan \| Consultant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of restricted stock awards	13,577
2020 Stock Option and Grant Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Cumulative increase in number shares reserved for issuance, percentage		5.00%
Maximum aggregate number of shares of stock issued		15,250,000
2020 Stock Option and Grant Plan \| Stock Available For Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for issuance			3,414,594		3,414,594
Shares available for future grants			1,525,092		1,525,092
2020 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Annual increase in number of shares reserved for issuance		53,161
Reserved shares of common stock for issuance			172,487		172,487
Percentage of payroll deductions of base salary or wages		15.00%
Percentage of maximum discount on purchase of shares of common stock		15.00%
Offering period, description					(i) on the first trading day of the offering period or (ii) the last day of any offering period. The Company utilizes the Black Scholes option pricing model to compute the fair market value of the shares and stock-based compensation expense is recognized over the offering period. Six-month offering periods commence each January 1 and July 1 during the term of the plan, with the plan administrator having the right to establish different offering periods.
Cumulative increase in number shares reserved for issuance, percentage		1.00%
2020 Employee Stock Purchase Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Base salary or wages		$ 25,000
2020 Employee Stock Purchase Plan \| Stock Available For Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for issuance			172,487		172,487		119,326

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Jun. 30, 2026
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) (Parenthetical)	6 Months Ended
	Jun. 30, 2026
Statement of Stockholders' Equity [Abstract]
Common stock exchange ratio	0.2016

Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2024	$ (96,616)			$ 19,945		$ (116,561)
Balance, Shares at Dec. 31, 2024			1,356,431
Temporary Equity Balance at Dec. 31, 2024		$ 45,999
Temporary Equity Balance, Shares at Dec. 31, 2024		43,151,340
Premium on issuance of convertible promissory notes	186			186
Issuance of Series B-2 redeemable convertible preferred stock upon conversion of convertible promissory notes in connection with the Merger		$ 3,695
Issuance of Series B-2 redeemable convertible preferred stock upon conversion of convertible promissory notes in connection with the Merger, Shares		794,499
Conversion of convertible promissory notes into common stock in connection with the Merger	20,799			20,799
Conversion of convertible promissory notes into common stock in connection with the Merger, Shares			3,418,839
Conversion of redeemable convertible preferred stock into common stock in connection with the Merger		$ (49,694)
Conversion of redeemable convertible preferred stock into common stock in connection with the Merger, Shares		(43,945,839)
Conversion of redeemable convertible preferred stock into common stock in connection with the Merger	49,694		$ 1	49,693
Conversion of redeemable convertible preferred stock into common stock in connection with the Merger, Shares			8,859,474
Recognition of AlloVir common stock outstanding at the closing of the Merger	104,990		$ 1	104,989
Recognition of AlloVir common stock outstanding at the closing of the Merger, Shares			5,067,674
Transaction costs related to the Merger	(5,357)			(5,357)
Stock-based compensation expense	374			374
Net loss	(10,196)					(10,196)
Balance at Mar. 31, 2025	63,874		$ 2	190,629		(126,757)
Balance, Shares at Mar. 31, 2025			18,702,418
Balance at Dec. 31, 2024	$ (96,616)			19,945		(116,561)
Balance, Shares at Dec. 31, 2024			1,356,431
Temporary Equity Balance at Dec. 31, 2024		$ 45,999
Temporary Equity Balance, Shares at Dec. 31, 2024		43,151,340
Proceeds from exercise of stock options, Shares	0
Unrealized loss on marketable securities, net of tax	$ 0
Net loss	(21,546)
Balance at Jun. 30, 2025	53,115		$ 2	191,220		(138,107)
Balance, Shares at Jun. 30, 2025			18,702,418
Balance at Mar. 31, 2025	63,874		$ 2	190,629		(126,757)
Balance, Shares at Mar. 31, 2025			18,702,418
Stock-based compensation expense	591			591
Unrealized loss on marketable securities, net of tax	0
Net loss	(11,350)					(11,350)
Balance at Jun. 30, 2025	53,115		$ 2	191,220		(138,107)
Balance, Shares at Jun. 30, 2025			18,702,418
Balance at Dec. 31, 2025	78,814		$ 2	238,805	$ 6	(159,999)
Balance, Shares at Dec. 31, 2025			22,902,418
Proceeds from exercise of stock options	74			74
Proceeds from exercise of stock options, Shares			89,873
Stock-based compensation expense	580			580
Unrealized loss on marketable securities, net of tax	(55)				(55)
Net loss	(10,856)					(10,856)
Balance at Mar. 31, 2026	68,557		$ 2	239,459	(49)	(170,855)
Balance, Shares at Mar. 31, 2026			22,992,291
Balance at Dec. 31, 2025	$ 78,814		$ 2	238,805	6	(159,999)
Balance, Shares at Dec. 31, 2025			22,902,418
Proceeds from exercise of stock options, Shares	102,576
Unrealized loss on marketable securities, net of tax	$ (79)
Net loss	(22,371)
Balance at Jun. 30, 2026	57,672		$ 2	240,113	(73)	(182,370)
Balance, Shares at Jun. 30, 2026			23,804,981
Balance at Mar. 31, 2026	68,557		$ 2	239,459	(49)	(170,855)
Balance, Shares at Mar. 31, 2026			22,992,291
Proceeds from exercise of stock options	10			10
Proceeds from exercise of stock options, Shares			12,703
Issuance of common stock upon exercise of pre-funded warrants, Shares			799,987
Stock-based compensation expense	644			644
Unrealized loss on marketable securities, net of tax	(24)				(24)
Net loss	(11,515)					(11,515)
Balance at Jun. 30, 2026	$ 57,672		$ 2	$ 240,113	$ (73)	$ (182,370)
Balance, Shares at Jun. 30, 2026			23,804,981

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Accrued expenses and other current liabilities	$ 7,267	$ 8,117
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	23,804,981	22,902,418
Common stock, shares outstanding	23,804,981	22,902,418
Related Party
Accrued expenses and other current liabilities	$ 40	$ 67

Segment Reporting

6 Months Ended

Jun. 30, 2026

Segment Reporting [Abstract]

Segment Reporting

17. Segment Reporting

The Company operates and manages its business as one reportable and operating segment. The Company's Chief Executive Officer is the Company's chief operating decision maker (the “CODM”). The CODM reviews and evaluates net loss, as reported in the condensed consolidated statements of operations and comprehensive loss, for purposes of assessing performance, making operating decisions, allocating resources, and planning and forecasting for future periods on an aggregate basis. The CODM does not review assets at a different level or category than the amounts disclosed in the condensed consolidated balance sheets as total assets. All of the Company’s long-lived assets are located in the United States.

The following is the Company’s summary of segment loss, including significant segment expenses for the three and six months ended June 30, 2026 and 2025 (in thousands):


	Three Months Ended June 30,						Six Months Ended June 30,
	2026			2025			2026			2025
External research and development expenses:
CDMO, CRO and other third-party clinical trials and consulting costs	$	7,395		$	6,915		$	13,608		$	11,727
Internal research and development personnel costs		1,496			1,175			2,770			2,244
Other research and development costs		127			350			212			499
General and administrative personnel expenses		1,220			1,094			2,785			1,771
Other general and administrative expenses		2,148			2,722			4,844			6,369
Interest expense		—			—			—			1,443
Other segment items1		(871	)		(906	)		(1,848	)		(2,507	)
Net loss	$	(11,515	)	$	(11,350	)	$	(22,371	)	$	(21,546	)

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

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+ Details

Related Parties

6 Months Ended

Jun. 30, 2026

Related Parties

15. Related Parties

Samsara BioCapital L.P. and Affiliates

Since the Company’s inception, Samsara has provided in-kind research and development and general and administrative services to the Company. From April 2022, Samsara also began to provide general and administrative services for cash consideration related to (i) accounting and controllership, (ii) human resources, and (iii) executive assistance. In July 2023, the Company and Samsara entered into a Business Services Agreement (the “BSA”) that governs the provision of such services. The BSA has a term of five years and may be terminated upon 15 days written notice by either party.

The Company recognized general and administrative expense related to services provided by Samsara under the BSA of $0.1 million and $0.04 million for the three months ended June 30, 2026 and 2025, respectively, and $0.2 million for each of the six months ended June 30, 2026 and 2025.

No capital contributions related to services provided by Samsara were recognized for the three and six months ended June 30, 2026 and 2025 as Samsara stopped providing in-kind services in July 2024.

As of June 30, 2026 and December 31, 2025, the Company recognized $0.05 million and $0.1 million in accrued expenses and other current liabilities in the condensed consolidated balance sheets related to the services provided by Samsara under the BSA. As of June 30, 2026 and December 31, 2025, the Company recognized immaterial amounts in accounts payable in the condensed consolidated balance sheets related to the services provided by Samsara under the BSA. The Company recognized a $32.1 million royalty obligation - related party, as a long-term liability, under the Royalty Agreement as of June 30, 2026 and December 31, 2025.

The Company issued Samsara convertible promissory notes (Note 8), redeemable convertible preferred stock and common stock. In July 2024, the Company entered into a Royalty Agreement with Samsara (Note 7).

Members of the Company’s board of directors received $0.02 million and $0.03 million in consulting fees for each of the three and six months ended June 30, 2026, respectively.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480990/946-20-50-5

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 6
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 2
-Subparagraph (c)
-Publisher FASB
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
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-URI https://asc.fasb.org/1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483326/850-10-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
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-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483326/850-10-50-1

+ Details

Significant Agreements

6 Months Ended

Jun. 30, 2026

Significant Agreements [Abstract]

Significant Agreements

7. Significant Agreements

License Agreement with the University of California, San Diego

In April 2021, the Company entered into a license agreement with UCSD (as amended, the “UCSD Agreement”) pursuant to which the Company obtained (i) an exclusive license under the patent rights to make, use, sell, offer for sale, and import licensed products and (ii) a non-exclusive license to use the technology with a right to sublicense, each (i) and (ii) related to new anti-VEGF agents and novel long-acting VEGF inhibitors for intraocular neovascularization for the treatment of patients with retinal pathologies. As partial consideration for the license, the Company agreed to pay UCSD $0.2 million and was obligated to issue shares of its common stock to UCSD equal to 5% of the fully diluted issued and outstanding securities of the Company until such time as an aggregate of $5.0 million in gross proceeds from the sale of equity securities had been raised by the Company. In June 2022, after the closing of the Series A financing, the Company issued 137,234 shares of its common stock to UCSD. The Company was also obligated to pay $0.1 million of patent costs incurred prior to the effective date and is required to reimburse future patent expenses incurred by UCSD during the term of the UCSD Agreement. Under the UCSD Agreement, the Company is required to make annual license maintenance payments of $10,000 during the first four anniversaries and $15,000 on the fifth and every subsequent anniversary of the effective date. The Company is obligated to pay an aggregate of up to $4.6 million upon the achievement of various development and regulatory milestones and low single-digit royalties on net sales of licensed products. The royalty is payable, on a licensed product-by-licensed product and country-by country basis, until expiration of the last-to-expire issued patent of the applicable licensed product in the country of sale or the manufacture. If the Company enters into a sublicensing agreement, it is required to pay UCSD a sublicense fee as a percentage of the fair market value of any sublicense fee received that is not earned royalties for each sublicense granted. The sublicense fee percentage ranges from 50% if the applicable sublicense agreement is entered into within one year from the UCSD Agreement effective date and decreases to 10% if the applicable sublicense agreement is entered into after the first dosing of a patient for a phase 2 clinical trial.

In case of a closing of a merger, or sale of at least 50% of the voting stock of the Company or the sale by the Company of all or substantially all of its assets (collectively referred to as “Liquidity Event”), the Company is obligated to make a one-time cash milestone payment to UCSD ranging from $0.1 million to $1.0 million based on the valuation of the Company’s outstanding shares at the Liquidity Event closing date. The Merger did not meet the definition of the Liquidity Event.

The UCSD Agreement is effective until the expiration date of the longest-lived patent rights or last to be abandoned patent or future patent of the licensed products, whichever is later. The Company can terminate the agreement upon 60 days written notice. UCSD can terminate the agreement in the event of an uncured material breach, such as a failure to make payments due, or to perform under the UCSD Agreement or a violation of any other material term of the UCSD Agreement, that is not cured by the Company within 60 days after a written breach notice provided by UCSD.

The acquisition of the license under the UCSD Agreement, including patent rights and know-how, was accounted for as an asset acquisition. As the acquired technology did not have an alternative future use, the Company recognized the $0.2 million initial cash consideration, $0.1 million patent reimbursement costs incurred prior to the effective date, and $0.2 million related to the obligation to issue shares of the Company’s common stock as research and development expenses. The obligation to issue shares of common stock included two components, the initial shares obligation and the additional shares obligation. The fair value of the initial share obligation was estimated as $0.1 million based on the fair value of 55,440 shares of common stock, which represented 5% of the outstanding fully diluted equity at the effective date. As the initial share obligation was indexed to the Company’s own stock, it was recorded as additional paid-in capital. The additional shares obligation was recognized when the next round of financing closed in March 2022. The Company estimated the fair value of an additional 81,794 shares of common stock as $0.2 million and recognized it as research and development expenses and additional paid-in capital in March 2022. The Company concluded that the contingent payment upon the closing of the Liquidity Event is a derivative liability and should be accounted for at fair value and re-measured until its settlement or expiration. The Company recognized an immaterial amount in patent reimbursement costs for the three and six months ended June 30, 2026. The Company recognized an immaterial amount and $0.1 million in patent reimbursement costs for each of the three and six months ended June 30, 2025, respectively. As of June 30, 2026 and December 31, 2025, the Company recognized an immaterial amount related to the UCSD Agreement in accrued expenses and other current liabilities in the condensed consolidated balance sheets. Over the life of the agreement through June 30, 2026, development milestones totaling $0.1 million have been achieved by the Company and incurred as research and development expenses. The Company did not achieve any development milestones and did not incur any related milestone expense during the three and six months ended June 30, 2026 and 2025. The assignment fee derivative liability fair value was estimated to be zero as of June 30, 2026 and December 31, 2025, as the probability of the Liquidity Event was estimated to be zero.

Royalty Agreement with Samsara – Related Party

In July 2024, the Company entered into a royalty agreement (the “Royalty Agreement”) with Samsara, the majority stockholder of the Company and a related party. Under the Royalty Agreement, the Company redeemed 10,080 shares of its common stock issued

to Samsara under a restricted stock purchase agreement in exchange for the Company’s agreement to pay Samsara a low single-digit percentage tiered royalty on net sales, if any, of the Company’s products developed using the technology licensed under the UCSD Agreement. Such royalties are payable on a product-by-product and country-by-country basis until the later of (i) ten years after the first commercial sale of such product in such country and (ii) the expiration of the last-to-expire issued claim of the Company’s patents for such product in such country.

The Company identified two elements in the Royalty Agreement: repurchased shares, and future royalty payments to Samsara. The repurchase of shares was accounted at an estimated fair value of $32,000 as a reduction of common stock and additional paid-in-capital in the condensed consolidated balance sheet and the statement of redeemable convertible preferred stock and shareholders’ deficit. The Company recorded $32.1 million as a long-term liability related to the obligation to make royalty payments to Samsara. The fair value of the royalty obligation was estimated using a risk-adjusted net present value model, based on the contractual royalty rates applied to the future net sales forecast, adjusted by the probability of success of product development and discounted to the effective date of the Royalty Agreement using a 25.0% discount rate. The excess of the royalty liability over the fair value of the repurchased shares of $32.0 million was recorded as a research and development expense in July 2024. Once royalty payments to Samsara are deemed probable and estimable, and if such amounts exceed the initially recorded royalty obligation balance, the Company will impute interest to accrete the liability on a prospective basis based on such estimates. If and when the Company makes royalty payments under the Royalty Agreement, the royalty obligation balance will be reduced.

From July 2024 through June 30, 2026, royalty payments were not probable and estimable and, therefore, no interest expense was recognized for the royalty liability.

Defined Contribution Plan

6 Months Ended

Jun. 30, 2026

Retirement Benefits [Abstract]

Defined Contribution Plan

16. Defined Contribution Plan

The Company sponsors a 401(k) plan (the “401(k) Plan”), which is designed to be qualified under Section 401(k) of the Internal Revenue Code of 1986, as amended. Eligible employees can elect to contribute to the 401(k) Plan, subject to certain limitations on eligible compensation. The Company may match employee contributions in amounts to be determined at the Company’s sole discretion. The Company’s matching contributions during each of the three and six months ended June 30, 2026 and 2025 were immaterial.

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Research and development expenses	$ 9,018	$ 8,440	$ 16,590	$ 14,470
General and administrative expenses	3,368	3,816	7,629	8,140
Change in fair value of tranche liability	0	0	0	365
Change in fair value of derivative liability	0	0	0	1,229
Interest expense	0	0	0	1,443
Loss on extinguishment and on issuance of convertible promissory notes	0	0	0	(186)
Related Party
Research and development expenses	15	12	30	25
General and administrative expenses	93	37	160	188
Change in fair value of tranche liability	0	0	0	331
Change in fair value of derivative liability	0	0	0	1,165
Interest expense	0	0	0	1,384
Loss on extinguishment and on issuance of convertible promissory notes	$ 0	$ 0	$ 0	$ 169

- Definition

Amount of interest expense classified as operating and nonoperating. Includes, but is not limited to, cost of borrowing accounted for as interest expense.

+ References

+ Details

Balance Sheet Components (Tables)

6 Months Ended

Jun. 30, 2026

Balance Sheet Related Disclosures [Abstract]

Schedule of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets as of June 30, 2026 and December 31, 2025 consisted of the following (in thousands):


	June 30,		December 31,
	2026		2025
Prepaid research and development expenses	$	778	$	323
Prepaid insurance		509		185
Prepaid taxes		365		211
Prepaid professional and legal costs		—		30
Other prepaid expenses and other current assets		217		78
Total prepaid expenses and other current assets	$	1,869	$	827

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities as of June 30, 2026 and December 31, 2025 consisted of the following (in thousands):


	June 30,		December 31,
	2026		2025
Accrued research and development expenses	$	5,901	$	4,295
Accrued compensation expense		865		1,601
Accrued professional and legal costs		466		442
Accrued transaction expenses		—		1,717
Other accrued expenses and other current liabilities		35		62
Total accrued expenses and other current liabilities	$	7,267	$	8,117

Commitments and Contingencies - Additional Information (Details) - USD ($)		1 Months Ended	3 Months Ended		6 Months Ended		63 Months Ended
	Apr. 14, 2025	Apr. 30, 2021	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026
Loss Contingencies [Line Items]
Research and development expenses			$ 9,018,000	$ 8,440,000	$ 16,590,000	$ 14,470,000
Accrued royalties noncurrent			32,100,000		32,100,000		$ 32,100,000
Date of settlement agreement executed	Apr. 14, 2025
Agreement of settlement resolving the claims in the Securities Class Action subject to Court approval	$ 1,000,000
Royalities due			0		0		0
University of California, San Diego \| License Agreement
Loss Contingencies [Line Items]
Research and development expenses		$ 200,000	$ 0	$ 0	$ 0	$ 0	$ 100,000

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 275
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-4

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
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-Paragraph 9
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-URI https://asc.fasb.org/1943274/2147483076/450-20-50-9

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/1943274/2147483359/720-20-50-1

Reference 5: http://www.xbrl.org/2003/role/exampleRef
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-Name Accounting Standards Codification
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-Paragraph 27
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482395/460-10-55-27

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 9
-Subparagraph (b)
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-1

+ Details

Segment Reporting - Additional Information (Details)	6 Months Ended
Segment Reporting - Additional Information (Details)	Jun. 30, 2026 Segment
Segment Reporting [Abstract]
Number of reportable segments	1
Number of operating segments	1
Segment Reporting, CODM, Individual Title and Position or Group Name [Extensible Enumeration]	srt:ChiefExecutiveOfficerMember
Segment Reporting, CODM, Profit (Loss) Measure, How Used, Description	The CODM reviews and evaluates net loss, as reported in the condensed consolidated statements of operations and comprehensive loss, for purposes of assessing performance, making operating decisions, allocating resources, and planning and forecasting for future periods on an aggregate basis.

Commitments and Contingencies

6 Months Ended

Jun. 30, 2026

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

10. Commitments and Contingencies

Leases

The Company’s commitments under its operating lease are described in Note 9.

Research and Development Agreements

The Company enters into various agreements in the ordinary course of business, such as those with suppliers, contract development and manufacturing organizations, clinical research organizations, and other research and development vendors. These agreements provide for termination at the request of either party, generally with less than one year’s notice. Therefore, they are cancellable contracts and, if canceled, are not expected to have a material effect on the Company’s financial condition, results of operations, or cash flows.

License and Royalty Agreements

The Company is required to pay certain milestone payments contingent upon the achievement of specific development and regulatory events in accordance with the UCSD Agreement (Note 7). Over the life of the agreement through June 30, 2026, the Company achieved development milestones totaling $0.1 million, which were recorded as research and development expenses. No other milestones were achieved or probable as of June 30, 2026 and December 31, 2025. The Company is required to pay royalties on commercial sales of products developed under the UCSD Agreement. The Company’s product candidate was in clinical development as of June 30, 2026, and no such royalties were due.

The Company is obligated to pay royalties to Samsara under the Royalty Agreement (Note 7). The Company recognized an initial royalty obligation liability in the amount of $32.1 million, which was based on its estimated fair value at the effective date of the Royalty Agreement. Once royalty payments to Samsara are deemed probable and estimable, and if such amounts exceed the royalty liability balance, the Company will impute interest to accrete the royalty obligation on a prospective basis based on such estimates. As of June 30, 2026, these royalties were not probable and estimable.

Legal Contingencies

The Company, from time to time, may be a party to litigation arising in the ordinary course of business. If the potential loss from any claim, asserted or unasserted, or legal proceeding is considered probable and the amount is reasonably estimable, the Company will accrue a liability for the estimated loss.

Litigation Related to the Merger

Two complaints were filed by purported AlloVir stockholders as individual actions against AlloVir and the members of its board of directors in the Supreme Court of the State of New York, New York County, captioned Keller v. AlloVir, Inc. et al., No. 650989/2025 (N.Y. Sup. Ct. Feb. 20, 2025), and Morgan v. AlloVir, Inc. et al., No. 650965/2025 (N.Y. Sup. Ct. Feb. 19, 2025) (the “Complaints”). The Complaints alleged that the proxy statement/prospectus describing the transaction between Legacy Kalaris and AlloVir misrepresented and/or omitted certain purportedly material information, and assert claims for negligent misrepresentation and concealment and negligence under New York common law. The Company has not recorded any liabilities in connection with the Complaints, and the Complaints were voluntarily dismissed on April 23, 2026.

Litigation Related to Legacy Operations of AlloVir

On January 19, 2024, a purported stockholder of AlloVir filed a lawsuit, captioned Zerbato v. AlloVir, Inc. et al., No. 1:24-cv-10152 (D. Mass.) (the “Securities Class Action”), in the U.S. District Court for the District of Massachusetts (the “Court”) against AlloVir and two of its officers purportedly on behalf of a putative class of stockholders. On April 16, 2024, the Court appointed stockholders Harry Levin and Julio Maurice Bueno as lead plaintiffs and their counsel as lead counsel in the action. On June 17, 2024, lead plaintiffs filed their amended complaint. In the amended complaint, lead plaintiffs asserted claims purportedly on behalf of a putative class of stockholders consisting of persons who purchased or otherwise acquired AlloVir securities between January 11, 2023 and December 21, 2023, inclusive. The amended complaint asserted claims under Sections 10(b) and 20(a) of the Securities Exchange Act of 1934, as amended, and the related regulations, alleging that the defendants made false and misleading statements and omissions to investors relating to AlloVir’s three Phase 3 studies of posoleucel. The complaint sought, among other things, damages, prejudgment and post-judgment interest, and attorneys’ fees, expert fees and other costs. On April 14, 2025, the parties executed a definitive stipulation and agreement of settlement resolving the claims in the Securities Class Action for $1.0 million. On July 30, 2025, the Court entered an order granting final approval of the settlement and dismissing the Securities Class Action with prejudice.

On October 21, 2024, a purported AlloVir stockholder filed a derivative lawsuit, captioned Lister v. Brainard et al., No. 1:24-cv-12658 (D. Mass.), in the U.S. District Court for the District of Massachusetts against certain of AlloVir’s officers and directors and naming AlloVir as a nominal defendant. The derivative complaint alleged, purportedly on behalf of AlloVir, violations of Section 14(a) of the Securities Exchange Act of 1934, breach of fiduciary duties, unjust enrichment, waste of corporate assets, gross mismanagement, and abuse of control against the individual defendants and contribution under Sections 10(b) and 21D of the Securities Exchange Act of 1934 against Dr. Brainard and Mr. Sinha. These claims were based on substantially identical allegations as the complaint in the above-listed Securities Class Action. The lawsuit sought, among other things, an award of damages and restitution in favor of AlloVir, certain changes to AlloVir’s corporate governance, and attorneys’ fees and costs. On August 1, 2025, the plaintiff filed a notice voluntarily dismissing the derivative lawsuit without prejudice.

Guarantees and Indemnifications

In the normal course of business, the Company enters into agreements that contain a variety of representations and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. As of June 30, 2026 and December 31, 2025, the Company does not have any material indemnification claims that were probable or reasonably possible.