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 ($)					1 Months Ended	3 Months Ended				6 Months Ended		12 Months Ended
	Aug. 07, 2025	Jun. 11, 2025	May 19, 2025	Oct. 23, 2019	Jul. 31, 2026	Jun. 30, 2026	Mar. 31, 2026	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2026	Jun. 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			$ 3,021,000
Common stock issuance						$ 140,201,000
Warrants exercised										10,800,000
Additional common stock warrants issued						3,090,190				3,090,190
Common Stock Warrants Exercised										$ 66,000	$ 0
Weighted average grant-date fair value of stock options granted										$ 2.83	$ 1.46
Unrecognized compensation cost related to unvested stock-based awards						$ 35,488,000				$ 35,488,000
Unrecognized compensation cost, period for recognition										2 years 3 months 18 days
Proceeds from issuance of common stock upon exercise of common stock warrants										$ 13,188,000	$ 0
Shares remaining available for issuance						1,063,618				1,063,618
Employee Stock Option
Class Of Stock [Line Items]
Stock-based compensation expense						$ 5,499,000		$ 5,705,000		$ 10,755,000	$ 10,866,000
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			$ 1,813,000
Unvested Stock Option
Class Of Stock [Line Items]
Stock-based compensation expense			$ 1,208,000
At-The-Market Offering Sales Agreement
Class Of Stock [Line Items]
Common stock issuance	$ 150,000,000								$ 200,000,000
Proceeds from issuance of common stock upon exercise of common stock warrants												$ 2,595,000	$ 5,129,000
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		$ 7,724,000										$ 10,151,000
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										$ 13,188,000
Common Stock Warrants Exercised										5,275,100,000
May 2026 Financing
Class Of Stock [Line Items]
Common stock issuance										$ 140,201,000
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										10,132,367
Proceeds from issuance of common stock upon exercise of common stock warrants										$ 28,730,000
2025 Inducement Plan
Class Of Stock [Line Items]
Common stock issuance										$ 275,000
Common stock issuance, Shares										1,275,000
2025 Inducement Plan \| Employee Stock Option
Class Of Stock [Line Items]
Common stock issuance, Shares										1,000,000
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										4,166,000
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										$ 25,000
Percentage of shares to be purchased										85.00%
Subsequent Event [Member]
Class Of Stock [Line Items]
Common stock issuance, Shares					1,802,770
Proceeds from issuance of common stock upon exercise of common stock warrants					$ 5,547,000
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						167,726,537				167,726,537		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, outstanding shares						47,815,090				47,815,090
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										$ 93,558,000
Warrants exercised										4,800,000