7.

Stock-based compensation

Summary of plans and activity

In June 2001, our Board of Directors and stockholders established the 2001 Stock Incentive Award Plan (“2001 Plan”). Under the 2001 Plan, as amended, 2,674,749 shares of common stock had been reserved for the issuance of incentive stock options granted to employees, non-employee directors, consultants, or independent contractors. Options granted under the 2001 Plan have vesting terms that range from the date of grant to four years and expire within a maximum term of 10 years from the grant date.

In 2021, our Board of Directors and stockholders established the 2021 Equity Incentive Plan (“2021 Plan”). The number of shares of common stock initially reserved for issuance under the 2021 Plan was 1,854,490 newly reserved shares in addition to the 600,737 shares that remained available for issuance under the 2001 Plan. The shares available for issuance under the 2021 Plan automatically increase on the first day of each year, commencing January 1, 2022, and ending on (and including) January 1, 2031, in an amount equal to 5% of the total number of shares of our common stock outstanding on the last day of the calendar month before the date of each automatic increase, or such lesser number of shares as determined by the Board of Directors. The annual increase resulted in an additional 1,043,959 shares being reserved for issuance under the 2021 Plan as of January 1, 2024. The 2021 Plan provides for the issuance of stock options, stock appreciation rights, restricted stock awards, stock unit awards and other stock-based awards and cash incentive awards to employees, consultants and non-employee directors of the Company and its subsidiaries. Awards granted under the 2021 Plan will have such vesting schedules and other terms as determined by the Compensation Committee and stock options and stock appreciation rights have a maximum term of 10 years from the grant date. No further awards can be made under the 2001 Plan following the adoption of the 2021 Plan. As of December 31, 2025, there were 1,447,051 shares available for future issuance under the 2021 Plan.

Stock Options

Options are granted at exercise prices not less than the fair market value of our common stock on the date of grant. Prior to our IPO, the fair market value of our common stock was determined by our Board of Directors, and following our IPO, the fair market value of our common stock is based on the closing price of our common stock on the date of grant.

During the years 2008 through the IPO, the Board of Directors authorized the grant of stock options for the purchase of shares of common stock to the employers of certain non-employee directors. The options were not granted under the 2001 Plan or the 2021 Plan, but terms are substantially the same as our standard form of option agreement for non-employee directors as they have an exercise price not less than the fair market value on the grant date and vest over 48 months from the date of grant.

The following is a summary of stock option activity:

  ​ ​ ​

  ​ ​ ​

Weighted 

  ​ ​ ​

Number 

Average 

Aggregate 

of 

Exercise 

Intrinsic 

Options

Price

Value

 

(in thousands)

Balance as of December 31, 2023

4,488,845

$

9.77

$

97,266

Granted

3,237,758

$

12.77

Cancelled / Forfeited

(1,665,515)

$

10.16

Exercised

(510,669)

$

5.28

Balance as of December 31, 2024

 

5,550,419

$

11.81

 

$

18,771

Granted

 

1,050,622

$

11.56

 

  ​

Cancelled / Forfeited

 

(471,789)

$

15.10

 

  ​

Exercised

 

(294,804)

$

2.69

 

  ​

Balance as of December 31, 2025

 

5,834,448

$

11.96

$

2,459

Options exercisable as of December 31, 2025

 

3,693,233

$

11.24

$

2,386

As of December 31, 2025, stock options outstanding included 4,363 options that were not granted under the 2001 Plan or the 2021 Plan. For options outstanding as of December 31, 2025, the weighted average remaining contractual life was 6.6 years. For options exercisable as of December 31, 2025, the weighted average remaining contractual life was 5.6 years. As of December 31, 2025, unrecognized compensation expense related to unvested stock-based compensation arrangements for stock options was $18.2 million. As of December 31, 2025, the related weighted average period over which the expense is expected to be recognized is approximately 2.4 years

Restricted Stock Units

RSUs are share awards that entitle the holder to receive freely tradable shares of our common stock upon vesting. The RSUs cannot be transferred and the awards are subject to forfeiture if the holder’s service terminates prior to vesting other than for death, disability, or other qualifying terminations.

The following is a summary of RSU activity:

  ​ ​ ​

  ​ ​ ​

Weighted 

  ​ ​ ​

Number 

Average 

Aggregate 

of 

Grant Date

Intrinsic 

RSUs

Fair Value

Value

 

(in thousands)

Unvested Balance as of December 31, 2024

 

$

$

Granted

 

393,928

 

12.13

 

  ​

Vested

 

 

 

  ​

Cancelled / Forfeited

 

(10,660)

 

12.96

 

  ​

Unvested Balance as of December 31, 2025

 

383,268

$

12.11

$

2,721

The aggregate intrinsic value of unvested RSUs is based on our closing stock price on the last trading day of the period. No RSUs were vested as of December 31, 2025. As of December 31, 2025, the unrecognized compensation expense related to unvested stock-based compensation arrangements for RSUs was $3.7 million. As of December 31, 2025, the related weighted average period over which the expense is expected to be recognized is approximately 3.2 years.

Employee Stock Purchase Plan

Our Board of Directors and stockholders also established an Employee Stock Purchase Plan (the “ESPP”). The number of shares of common stock initially reserved for issuance under the ESPP was 278,170. The shares available for issuance under the ESPP automatically increase on the first day of each year,

commencing January 1, 2022, and ending on (and including) January 1, 2031, in an amount equal to 1% of the total number of shares of our common stock outstanding on the last day of the calendar month before the date of each automatic increase, or such lesser number of shares as determined by the Board of Directors. The annual increase resulted in an additional 253,246 shares being reserved for issuance under the ESPP as of January 1, 2025. The ESPP permits certain of our U.S. employees to purchase shares of our common stock at a price per share not less than 85% of the lower of (i) the closing market price per share of our common stock on the first day of the applicable purchase period or (ii) the closing market price per share of our common stock on the purchase date at the end of the applicable six-month purchase period. For the year ended December 31, 2025, 148,657 shares of common stock were purchased under the ESPP for $0.8 million of employee contributions. As of December 31, 2025, there were 737,396 shares available for issuance under the ESPP.

Stock-based compensation expense

We use the Black-Scholes option pricing model to determine the fair value of stock options and ESPP purchase rights on the grant date. The fair value of RSUs is determined based on the closing stock price of our common stock on the grant date. We measure stock-based compensation expense based on the grant date fair value of the award and recognize compensation expense over the requisite service period, which is generally the vesting period for stock options and RSUs, and the offering period for ESPP purchase rights. The amount of stock-based compensation expense recognized for stock option and RSU awards during a period is based on the portion of the awards that are ultimately expected to vest. The amount of stock-based compensation expense recognized for ESPP purchase rights during a period is based on the estimated purchase rights as of the grant date. We account for forfeitures as they occur.

The following table provides the weighted average fair value of options granted to employees and the related assumptions used in the Black-Scholes option pricing model for the years ended December 31, 2025 and 2024:

  ​ ​ ​

December 31, 

2025

 

2024

Weighted average fair value of options granted

 

$

9.17

$

10.31

Expected term (in years) — non-officer employees

 

5.5 to 6.1

5.0 to 6.1

Expected term (in years) — officer employees

 

6.1 to 6.1

2.5 to 6.1

Expected volatility

 

95.0% to 103.1

%

87.7% to 98.9

%

Expected dividend yield

 

%

%

Risk-free interest rate

 

3.78% to 4.47

%

3.67% to 4.71

%

The following table provides the weighted average fair value of ESPP purchase rights and the related assumptions used in the Black-Scholes option pricing model for the years ended December 31, 2025 and 2024:

  ​ ​ ​

December 31, 

2025

 

2024

Weighted average fair value per ESPP purchase right

 

$

3.28

$

5.23

Expected term (in years) 

 

0.5

0.5

Expected volatility

 

112.3% to 133.4

%

74.0% to 96.9

%

Expected dividend yield

 

%

%

Risk-free interest rate

 

4.25% to 4.29

%

5.24% to 5.37

%

We review these assumptions on a periodic basis and adjust them, as necessary. We utilize the simplified method to develop the estimate of the expected term for stock option awards and ESPP purchase rights. The expected volatility is based upon our historical stock price. The expected dividend yield is assumed to be

zero, as we have never paid dividends and have no current plans to do so. The risk-free interest rate is based on the yield on U.S. Treasury securities for a period approximating the expected term of the options being valued.

The following table presents the components and classification of stock-based compensation expense for the periods indicated:

  ​ ​ ​

Year Ended

December 31, 

(in thousands)

2025

2024

Stock options

$

9,664

$

18,633

RSUs

900

Employee Stock Purchase Plan

488

417

Total stock-based compensation expense

$

11,052

$

19,050

Selling, general & administrative

$

9,810

$

17,746

Research & development

1,088

 

1,174

Cost of goods sold

154

 

130

$

11,052

$

19,050

On January 30, 2024, we amended the terms and conditions of certain stock option award agreements granted under the 2001 Plan and 2021 Plan between us and our former Chief Executive Officer in connection with his retirement, which occurred on February 11, 2024. The option agreements were amended to provide that, if not already vested at the time of termination of his employment due to retirement, the options will continue to vest on the previously scheduled vesting dates following his retirement, subject to his compliance with certain covenants. Additionally, the option agreements were modified so that the options may be exercised, to the extent vested, by our former Chief Executive Officer until the earlier of (a) five years following his retirement date, or (b) the applicable option expiration date. The modification of these option awards resulted in an additional $8.4 million of non-cash stock-based compensation expense recognized during the year ended December 31, 2024.

Historical Timeline

Fiscal YearFiled
2025Feb 13, 2026Showing above
2024Feb 18, 2025
2023Feb 9, 2024
2022Feb 10, 2023

About Stock Compensation Disclosures

Stock-based compensation disclosures detail the equity awards granted to employees and executives — including stock options, restricted stock units (RSUs), and performance shares — along with the valuation methods and assumptions used to expense them. This section reveals the true cost of talent retention and the alignment between management incentives and shareholder interests.

Key signals: total unrecognized compensation expense and its expected recognition period signal future earnings headwinds from already-granted awards. For stock options, examine Black-Scholes assumptions — expected volatility, risk-free rate, and expected term — as understating any of these reduces reported compensation expense. Compare stock compensation expense as a percentage of revenue against peers to assess dilution cost. Watch vesting schedules for acceleration clauses tied to change-of-control events. Performance-based awards with undemanding targets may indicate weak governance. Add back stock compensation to operating cash flow to calculate a more conservative free cash flow figure.