PLUS THERAPEUTICS, INC. Stock Compensation Disclosure

16. Stock-based Compensation

Under the Company’s 2015 New Employee Incentive Plan (the “2015 Plan”), awards may only be granted to employees who were not previously an employee or director of the Company, or following a bona fide period of non-employment, as a material inducement to entering into employment with the Company. As of December 31, 2025, there were 2,986,025 shares of common stock remaining and available for future issuances under the 2015 Plan.

The Company’s 2020 Stock Incentive Plan (the “2020 Plan”), which replaced the Company’s 2014 Equity Incentive Plan, provides for the award or sale of shares of common stock (including restricted stock), the award of stock units and stock appreciation rights, and the grant of both incentive stock options to purchase common stock to directors, officers, employees and consultants of the Company. The 2020 Plan, as amended, provides for the issuance of up to 21,303,334 shares of common stock, plus the number of shares available for issuance is increased to the extent that awards granted under the 2020 Plan and the Company’s 2014 Equity Incentive Plan are forfeited or expire (except as otherwise provided in the 2020 Plan). As of December 31, 2025, there were 6,864,306 shares remaining and available for future issuances under the 2020 Plan.

Generally, options issued under the 2020 Plan are subject to a two-year or four-year vesting schedule with 25% of the options vesting on the one year anniversary of the grant date followed by equal monthly installment vesting, and have a contractual term of 10 years.

A summary of stock option activity for the year ended December 31, 2025 is as follows:

The Company settles exercises of stock options with newly issued shares of its common stock. There were no stock options exercised in 2025 or 2024.

As of December 31, 2025, the total compensation cost related to non-vested stock options not yet recognized for all the Company’s plans is approximately $5.1 million, which is expected to be recognized as a result of vesting under service conditions over a weighted average period of 3.17 years.

The estimated fair value of options, including the effect of estimated forfeitures, is recognized over the requisite service period, which is typically the vesting period of each option. The fair value of each option awarded during the years ended December 31, 2025 and 2024 was estimated on the date of grant using the Black-Scholes-Merton option valuation model based on the following weighted-average assumptions:

The weighted average risk-free interest rate represents the interest rate for treasury constant maturity instruments published by the Federal Reserve Board. If the term of available treasury constant maturity instruments is not equal to the expected term of an

employee option, the Company uses the weighted average of the two Federal Reserve securities closest to the expected term of the employee option.

The dividend yield has been assumed to be zero as the Company (a) has never declared or paid any dividends and (b) does not currently anticipate paying any cash dividends on its outstanding shares of common stock in the foreseeable future.

Generally, restricted stock units represent the right to receive a certain number of shares of common stock subject to certain vesting conditions and other restrictions. The fair value of restricted stock units is determined by the closing market price on the grant date.

Restricted stock units granted during the year ended December 31, 2025 generally vest over a 36-month period upon satisfaction of service conditions. As of December 31, 2025, the total compensation cost related to non-vested restricted stock units not yet recognized for all the Company’s plans is approximately $1.1 million, which is expected to be recognized as a result of vesting under service conditions over a weighted average period of 2.53 years.