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Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2025

Stock-Based Compensation

Schedule of the Company's option activity

​

​	​	​	​	​	​	​	​	​	​	​
​	​	​	​	​	​	​	Weighted-	​	​	​
​	​	​	​	Weighted-		​	Average	​	​	​
​	​	​	​	Average		​	Remaining	​	Aggregate
​		​		Exercise			Contractual		Intrinsic
​	​	​	​	Price Per		​	Term	​	Value
​	​	Options	​	Share		​	(in years)	​	(in thousands)
Outstanding as of December 31, 2024		7,670,908	​	$	9.59		8.2	​	$	1,777
Stock options assumed in connection with the ACELYRIN Merger	​	4,712,186	​	$	12.99	​	​	​	​	​
Granted		6,983,120	​	$	4.60	​	​	​	​	​
Exercised		—	​	$	—	​	​	​	$	—
Forfeited or expired		(956,679)	​	$	9.07	​	​	​	​	​
Outstanding, vested and expected to vest as of September 30, 2025		18,409,535	​	$	8.60	​	7.0	​	$	388
Exercisable as of September 30, 2025	​	10,661,758	​	$	10.66	​	5.2	​	$	116

​

​	​	​	​	​	​	​	​	​	​	​	​
​		​		​	​		Weighted-			​	​
​	​	​	​	Weighted-		​	Average		​	​	​
​	​	​	​	Average		​	Remaining		​	Aggregate
​	​	​	​	Exercise		​	Contractual		​	Intrinsic
​	​	​	​	Price Per		​	Term		​	Value
​	​	Options	​	Share		​	(in years)		​	(in thousands)
Outstanding as of December 31, 2024		1,787,880	​	$	10.19		​	9.3	​	$	—
Granted		—	​	$	—		​	​	​
Forfeited or expired		(107,056)	​	$	10.19	​		​	​		​
Outstanding, vested and expected to vest as of September 30, 2025		1,680,824	​	$	10.19	​		8.6	​	$	—
Exercisable as of September 30, 2025		—	​	$	—	​		—	​	$	—

Schedule of various significant assumptions used to estimate the fair value of stock options

​

​	​	​	​	​
​	​	Nine Months Ended September 30,
​		2025		2024
Expected term (in years)	​	5.23 - 6.08		5.75 - 6.08
Volatility	​	98.84% - 104.32%		103.65% - 109.54%
Risk-free interest rate	​	3.69% - 4.65%		3.47% - 4.48%
Dividend yield	​	0.00%	​	0.00%

Schedule of activity for the Company's early exercisable shares

​

​	​	​	​	​	​
​	​	​	​	Weighted-
​	​	​	​	Average
​	​	Number of	​	Exercise Price
​		Shares		Per Share
Unvested as of December 31, 2024		146,683	​	$	5.53
Vested		(125,805)	​	$	4.96
Unvested as of September 30, 2025		20,878	​	$	8.96

schedule of estimating the fair value of the stock purchase rights under the ESPP

​

​	​	​
​	​	Nine Months Ended
​		September 30, 2025
Expected term (in years)	​	0.32 - 0.50
Volatility	​	79.42% - 133.00%
Risk-free interest rate	​	4.25% - 4.33%
Dividend yield	​	0.00%

Schedule of unvested RSU activity

​

​	​	​	​	​	​
​	​	​	​	Weighted-
​	​	​	​	Average
​	​	​	​	Grant Date
​	​	Number of	​	Fair Value
​		Shares		Per Share
RSUs assumed in connection with the ACELYRIN Merger		1,470,868	​	$	13.46
RSUs granted		2,449,945	​	$	3.95
RSUs released	​	(1,115,413)	​	$	13.76
RSUs forfeited		(134,495)	​	$	5.48
Unvested as of September 30, 2025		2,670,905	​	$	5.01

Schedule of the stock-based compensation expense

The following table summarizes the stock-based compensation expense recognized in the Company’s unaudited condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2025 and 2024 (in thousands):

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​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

Three Months Ended September 30,

​

Nine Months Ended September 30,

​

2025

2024

2025

2024

Research and development

​

$

5,773

​

$

3,720

​

$

16,717

​

$

6,805

General and administrative

​

4,014

​

​

3,589

​

​

18,700

​

​

6,294

Total stock-based compensation expense

​

$

9,787

​

$

7,309

​

$

35,417

​

$

13,099

The following table summarizes the stock-based compensation expense recognized in the Company’s unaudited condensed consolidated statements of operations and comprehensive loss by award type for the three and nine months ended September 30, 2025 and 2024 (in thousands):

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

Three Months Ended September 30,

​

Nine Months Ended September 30,

​

2025

2024

2025

2024

Stock options

​

$

7,979

​

$

7,291

​

$

28,771

​

$

13,045

RSUs

​

​

1,542

​

​

—

​

​

5,939

​

​

—

ESPP

​

​

266

​

​

—

​

​

701

​

​

—

Restricted stock awards

​

—

​

​

18

​

​

6

​

​

54

Total stock-based compensation expense

​

$

9,787

​

$

7,309

​

$

35,417

​

$

13,099

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Tabular disclosure of the changes in outstanding nonvested shares.

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Tabular disclosure of the number and weighted-average grant date fair value for restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock units that were granted, vested, or forfeited during the year.

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Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value.

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