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, 2025 USD ($) $ / shares shares	Jun. 30, 2024 USD ($)	Jun. 30, 2025 USD ($) $ / shares shares	Jun. 30, 2024 USD ($)	Dec. 31, 2024 $ / shares shares	Jan. 31, 2024 $ / shares shares
Business Acquisition [Line Items]
Redeemable convertible preferred stock, shares issued | shares			0		0		43,151,340
Price per share | $ / shares			$ 0.00001		$ 0.00001		$ 0.00001
Conversion ratios	0.201601						0.201601
Stock-based compensation expense			$ 591	$ 322	$ 965	$ 353
General and Administrative
Business Acquisition [Line Items]
Stock-based compensation expense			$ 378	$ 179	$ 658	$ 203
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							8,000,000	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