Cabaletta Bio, Inc. Quarterly report [Sections 13 or 15(d)]

Quarterly report [Sections 13 or 15(d)]

Common Stock - Additional Information (Details)

Common Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands					3 Months Ended				9 Months Ended		12 Months Ended
	Aug. 07, 2025	Jun. 11, 2025	May 19, 2025	Oct. 23, 2019	Sep. 30, 2026	Jun. 30, 2026	Sep. 30, 2025	Mar. 31, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025	Dec. 31, 2024	Jun. 09, 2026	Jan. 01, 2026	Jan. 01, 2025	Jun. 01, 2023	Jan. 31, 2019
Class Of Stock [Line Items]
Common stock, authorized shares					600,000,000				600,000,000		300,000,000		300,000,000
Increase in the Number of authorized shares					600,000,000				600,000,000
Warrant exercise price					$ 0.00001				$ 0.00001
Stock-based compensation expense			$ 3,021
Common stock issuance						$ 140,201
Warrants exercised									10,800,000
Additional common stock warrants issued					3,090,190				3,090,190
Common Stock Warrants Exercised									$ 167	$ 14
Weighted average grant-date fair value of stock options granted									$ 2.74	$ 1.46
Unrecognized compensation cost related to unvested stock-based awards					$ 31,668				$ 31,668
Unrecognized compensation cost, period for recognition									2 years 2 months 12 days
Proceeds from issuance of common stock upon exercise of common stock warrants									$ 128,217	$ 0
Shares remaining available for issuance					602,380				602,380
Employee Stock Option
Class Of Stock [Line Items]
Stock-based compensation expense					$ 5,264		$ 5,815		$ 16,019	$ 16,681
Stock Option Repricing
Class Of Stock [Line Items]
Share-based compensation unvested number of shares			9,900,096
Vested Stock Option
Class Of Stock [Line Items]
Stock-based compensation expense			$ 1,813
Unvested Stock Option
Class Of Stock [Line Items]
Stock-based compensation expense			$ 1,208
At-The-Market Offering Sales Agreement
Class Of Stock [Line Items]
Common stock issuance	$ 150,000							$ 200,000
Proceeds from issuance of common stock upon exercise of common stock warrants											$ 2,595	$ 5,129
2025 At The Market Offering Sales Agreement
Class Of Stock [Line Items]
Common stock issuance, Shares		2,609,865									4,160,176
Proceeds from issuance of common stock upon exercise of common stock warrants		$ 7,724									$ 10,151
June 2025 Financing
Class Of Stock [Line Items]
Common stock issuance, Shares									39,200,000
Common stock price per share					$ 2				$ 2
Net proceeds from exercise of warrants									$ 128,218
Common Stock Warrants Exercised									51,287,000
May 2026 Financing
Class Of Stock [Line Items]
Common stock issuance									$ 140,201
Common stock issuance, Shares									51,725,000
Common stock price per share					$ 2.9				$ 2.9
2025 Sales Agreement
Class Of Stock [Line Items]
Common stock issuance, Shares									12,057,202
Proceeds from issuance of common stock upon exercise of common stock warrants									$ 34,714
2025 Inducement Plan
Class Of Stock [Line Items]
Common stock issuance, Shares									1,275,000
Shares reserved for issuance					275,000				275,000
2025 Inducement Plan \| Employee Stock Option
Class Of Stock [Line Items]
Common stock issuance, Shares									700,000
2018 and 2019 Plan
Class Of Stock [Line Items]
Outstanding vested and unvested stock options, repricing			$ 1.92
2019 Plan
Class Of Stock [Line Items]
Common stock issuance, Shares									290,122
Shares reserved for issuance				2,342,288										234,229	4,019,172
Increase in share reserved percentage				4.00%
2019 Plan \| Employee Stock Option
Class Of Stock [Line Items]
Number of options granted									4,988,200
2019 ESPP
Class Of Stock [Line Items]
Shares reserved for issuance				234,229
Maximum \| Stock Option Repricing
Class Of Stock [Line Items]
Stock option exercise price			23.97
Minimum \| Stock Option Repricing
Class Of Stock [Line Items]
Stock option exercise price			$ 2.88
Minimum \| 2019 ESPP
Class Of Stock [Line Items]
Shares reserved for issuance																	234,229
Increase in share reserved percentage				1.00%
Payroll deduction percentage of eligible compensation									15.00%
Employee stock purchase plan maximum annual rights to purchase common stock									$ 25
Percentage of shares to be purchased									85.00%
Voting Common Stock
Class Of Stock [Line Items]
Common stock, authorized shares					593,590,481				593,590,481		293,590,481		293,590,481
Increase in the Number of authorized shares					(593,590,481)				(593,590,481)
Common stock, outstanding shares					215,720,392				215,720,392		100,479,323
Voting Common Stock \| 2019 Plan
Class Of Stock [Line Items]
Shares reserved for issuance																3,000,000
Non-voting Common Stock
Class Of Stock [Line Items]
Common stock, authorized shares					6,409,519				6,409,519		6,409,519
Increase in the Number of authorized shares					6,409,519				6,409,519
Pre-funded Warrants
Class Of Stock [Line Items]
Common stock, outstanding shares					6,000,000				6,000,000
Warrants exercised									10,800,000
Pre-funded Warrants \| June 2025 Financing
Class Of Stock [Line Items]
Common stock issuance, Shares									39,200,000
Common stock price per share					$ 1.99999				$ 1.99999
Decrease in exercise price of Warrents									$ 2.5
Net proceeds from exercise of warrants									$ 93,558
Warrants exercised									4,800,000