At the annual meeting of stockholders held on May 8, 2024, the Company’s stockholders approved, upon recommendation of the Board of Directors, the adoption of the ADTRAN Holdings, Inc. 2024 Employee Stock Incentive Plan (“2024 Employee Plan”) and the ADTRAN Holdings, Inc. 2024 Directors Stock Plan (“2024 Directors Plan”). No additional awards will be granted under the Company’s previous stock incentive plans, including the 2020 Employee Stock Incentive Plan, the 2020 Directors Stock Plan, or the 2015 Employee Stock Incentive Plan. Outstanding awards granted under the Company's prior equity incentive plans will remain subject to the terms of such applicable plans, and shares under such plans that are cancelled or forfeited will be available for issuance under the 2024 Employee Plan or the 2024 Directors Plan, as applicable.

Under the 2024 Employee Plan, the Company is authorized to issue 4.5 million shares of common stock to certain employees, key service providers and advisors through incentive stock options and non-qualified stock options, stock appreciation rights, RSUs and restricted stock, any of which may be subject to performance-based conditions. RSUs and restricted stock granted under the 2024 Employee Plan will typically vest pursuant to a four-year vesting schedule beginning on the first anniversary of the grant date. Stock options granted under the 2024 Employee Plan will typically become exercisable beginning after one year of continued employment, normally pursuant to a four-year vesting schedule beginning on the first anniversary of the grant date and have a ten-year contractual term. Stock options, RSUs and restricted stock granted under the 2024 Employee Plan reduce the shares authorized for issuance under the 2024 Employee Plan by one share of common stock for each share underlying the award. Forfeitures, cancellations and expirations of awards granted under the prior employee stock incentive plans increase the shares authorized for issuance under the 2024 Employee Plan by one share of common stock for each share underlying the award.

Under the 2024 Directors Plan, the Company is authorized to issue 0.6 million shares of common stock through stock options, restricted stock and RSUs to non-employee directors. Stock awards issued under the 2024 Directors Plan typically will become vested in full on the first anniversary of the grant date. Stock options issued under the 2024 Directors Plan will have a ten-year contractual term. Stock options, restricted stock and RSUs granted under the 2024 Directors Plan reduce the shares authorized for issuance under the 2024 Directors Plan by one share of common stock for each share underlying the award. Forfeitures, cancellations and expirations of awards granted under the prior directors stock plan increase the shares authorized for issuance under the 2024 Directors Plan by one share of common stock for each share underlying the award.

As of December 31, 2024, 5.1 million shares were available for issuance pursuant to awards that may be made in the future under stockholder-approved equity plans.

For the years ended December 31, 2024, 2023 and 2022, stock-based compensation expense was $15.3 million, $16.0 million and $28.3 million respectively.

The following table summarizes stock-based compensation expense related to stock options, PSUs, RSUs and restricted stock for the years ended December 31, 2024, 2023 and 2022:


(In thousands)	2024			2023			2022
Stock-based compensation expense included in cost of revenue	$	1,142		$	1,293		$	2,876
Selling, general and administrative expenses		10,412			10,701			20,844
Research and development expenses		3,788			4,022			4,602
Stock-based compensation expense included in operating expenses		14,200			14,723			25,446
Total stock-based compensation expense		15,342			16,016			28,322
Tax benefit for expense associated with non-qualified stock options, PSUs, RSUs and restricted stock		(2,102	)		(3,837	)		(5,152	)
Total stock-based compensation expense, net of tax	$	13,240		$	12,179		$	23,170

The following table is a summary of our PSUs, RSUs and restricted stock outstanding as of December 31, 2023 and 2024 and the changes that occurred during 2024:


	Number of shares (In thousands)			Weighted Average Grant Date Fair Value (Per Share)
Unvested PSUs, RSUs and restricted stock outstanding, December 31, 2023		1,942		$	17.46
PSUs, RSUs and restricted stock granted		1,097		$	7.85
PSUs, RSUs and restricted stock vested		(575	)	$	18.76
PSUs, RSUs and restricted stock forfeited		(129	)	$	14.20
Unvested PSUs, RSUs and restricted stock outstanding, December 31, 2024		2,335		$	13.22

The fair value of PSUs with performance conditions, RSUs and restricted stock is equal to the closing price of the Company's stock on the date of grant. The fair value of PSUs with market conditions is calculated using a Monte Carlo simulation valuation method.

The following table details the significant assumptions that impact the fair value estimate of the market-based PSUs:


	2024			2023			2022
Estimated fair value per share	$	8.29		$	19.26		$	24.01
Expected volatility		51.34	%		51.52	%		45.77	%
Risk-free interest rate		4.12	%		3.93	%		4.28	%
Expected dividend yield		—			2.55	%		1.76	%

For market-based PSUs, the number of shares of common stock earned by a recipient is subject to a market condition based on Adtran’s relative total stockholder return against all companies in the NASDAQ Telecommunications Index at the end of a three-year performance period. Depending on the relative total stockholder return over the performance period, the recipient may earn from 0% to 150% of the shares underlying the PSUs, with the shares earned distributed upon the vesting. The fair value of the award is based on the market price of our common stock on the date of grant, adjusted for the expected outcome of the impact of market conditions using a Monte Carlo Simulation valuation method. A portion of the granted PSUs vests and the underlying shares become deliverable upon the death or disability of the recipient or upon a change of control of Adtran, as defined by the 2020 Employee Plan. The recipients of the PSUs receive dividend credits based on the shares of common stock underlying the PSUs. The dividend credits vest and are earned in the same manner as the PSUs and are paid in cash upon the issuance of common stock for the PSUs.

During the year ended December 31, 2024, and 2023, the Company granted 0.1 and 0.9 million performance-based PSUs to its executive officers and certain employees, respectively. The grant-date fair value of these performance-based awards was based on the closing price of the Company’s stock on the date of grant. These awards vest over either a two or three-year period, subject to the grantee’s continued employment, with the ability to earn shares in a range of 0% to either 100% or 150% of the awarded number of PSUs based on the achievement of defined performance targets. Equity-based compensation expense and liabilities with respect to these awards may be adjusted over the vesting period to reflect the probability of achievement of performance targets defined in the award agreements.

During each of the years ended December 2023 and 2022, the Company granted 0.9 and 0.3 million performance-based PSUs to its executive officers and certain employees. The grant-date fair value of these performance-based awards was based on the closing price of the Company’s stock on the date of grant. These awards vested over one-year and two-year periods, respectively, subject to the grantee’s continued employment, with the ability to earn shares in a range of 0% to 142.8% of the awarded number of PSUs based on the achievement of defined performance targets. Equity-based compensation expense with respect to these awards may be adjusted over the vesting period to reflect the probability of achievement of performance targets defined in the award agreements. Pursuant to the Business Combination, the unearned performance-based PSUs converted to time-based RSUs which were treated as an award modification during the third quarter of 2022. This resulted in incremental compensation expense totaling $17.8 million being recognized during the twelve months ended December 31, 2022. These awards were fully vested as of December 31, 2022.

Pursuant to the Business Combination, 0.3 million shares of market-based PSU awards converted to time-based RSU awards which were treated as an award modification during the third quarter of 2022. Given that the fair value of these awards after the modification was less than the fair value of the awards immediately before the modification, no incremental compensation expense was recognized. The Company continued to recognize compensation expense based on the award's original grant date fair value.

The fair value of RSUs and restricted stock is equal to the closing price of our stock on the grant date. RSUs and restricted stock vest ratably over four-year and one-year periods, respectively.

We will continue to assess the assumptions and methodologies used to calculate the estimated fair value of stock-based compensation. If circumstances change, and additional data becomes available over time, we may change our assumptions and methodologies, which may materially impact our fair value determination.

As of December 31, 2024, total unrecognized compensation expense related to the non-vested portion of market-based PSUs, RSUs and restricted stock was approximately $10.7 million, which is expected to be recognized over an average remaining recognition period of 2.1 years. There was $10.9 million of unrecognized compensation expense related to unvested 2024 performance-based PSUs, which will be recognized over the remaining requisite service period of 1 years if achievement of the performance obligation becomes probable. Unrecognized compensation expense will be adjusted for actual forfeitures as they occur.

The following table is a summary of stock options outstanding as of December 31, 2024 and 2023 and the changes that occurred during 2024:


	Number of Options (In thousands)			Weighted Average Exercise Price (Per share)		Weighted Average Remaining Contractual Life in Years		Aggregate Intrinsic Value (In thousands)
Stock options outstanding, December 31, 2023		3,894		$	10.32		5.25	$	3,087
Stock options exercised		(139	)	$	5.93
Stock options forfeited		(202	)	$	6.78
Stock options expired		(609	)	$	14.69
Stock options outstanding, December 31, 2024		2,944		$	9.86		4.98	$	3,762
Stock options exercisable, December 31, 2024		1,465		$	8.73		4.18	$	1,960

As of December 31, 2024, there was $3.2 million of unrecognized compensation expense related to stock options which will be recognized over the remaining weighted-average period of 0.9 years. No stock options were granted during 2024.

The determination of the fair value of stock options assumed or granted by Adtran was estimated using the Monte Carlo method and is affected by its stock price, as well as assumptions regarding a number of complex and subjective variables that may have a significant impact on the fair value estimate. The stock option pricing model requires the use of several assumptions that impact the fair value estimate. These variables include, but are not limited to, the volatility of the Company's stock price and employee exercise behaviors.

All of the options were previously issued at exercise prices that approximated fair market value at the date of grant.

The aggregate intrinsic value of stock options represents the total pre-tax intrinsic value (the difference between the Company's closing stock price on the last trading day of the quarter and the exercise price, multiplied by the number of in-the-money options) that would have been received by the option holders had all option holders exercised their options on December 31, 2024. The amount of aggregate intrinsic value was $3.8 million as of December 31, 2024, which will change based on the fair market value of the Company's stock. The total pre-tax intrinsic value of options exercised during the years ended December 31, 2024 and 2023 was $0.3 million and $0.1 million, respectively.

The following table further describes our stock options outstanding as of December 31, 2024:


	Options Outstanding						Options Exercisable
Range of Exercise Prices (Per Share)	Options Outstanding at December 31, 2024 (In thousands)		Weighted Average Remaining Contractual Life in Years		Weighted Average Exercise Price (Per Share)		Options Exercisable at December 31, 2024 (In thousands)		Weighted Average Exercise Price
$5.23 – $5.23		1,131		8.87	$	5.23		550	$	5.23
$5.24 – $8.58		431		1.85	$	7.86		431	$	7.86
$8.59 – $12.17		696		2.81	$	11.57		155	$	9.49
$12.18 – $15.33		378		1.23	$	15.33		329	$	15.33
$15.34 – $19.08		308		4.37	$	19.08		—	$	—
		2,944						1,465

The Black-Scholes option pricing model (the “Black-Scholes Model”) is used to determine the estimated fair value of stock option awards on the date of grant. The Black-Scholes Model requires the input of certain assumptions that involve judgment. Because our stock options have characteristics significantly different from those of traded options, and because changes in the input assumptions can materially affect the fair value estimate, existing models may not provide reliable measures of fair value of our stock options. The stock

option pricing model requires the use of several assumptions that impact the fair value estimate. These variables include, but are not limited to, the volatility of our stock price and employee exercise behaviors.

The stock option pricing model requires the use of several assumptions that impact the fair value estimate. These variables include, but are not limited to, the volatility of our stock price and employee exercise behaviors.

The weighted-average estimated fair value of stock options granted to employees during the years ended December 31, 2023 was $2.99 per share with the following weighted-average assumptions:


		2023
Expected volatility	$		51.78	%
Risk-free interest rate			4.13	%
Expected dividend yield			—
Expected life (in years)			5.8	%