Total share-based expense related to stock options, RSUs and common stock awards was approximately $0.2 million and $0.3 million for the years ended December 31, 2024 and 2023, respectively. Share-based expense is classified in the consolidated statements of operations as follows:

Stock Options

The Company grants stock option awards and RSUs to employees and non-employees with varying vesting terms under the Xenetic Biosciences, Inc. Amended and Restated Equity Incentive Plan. The Company measures the fair value of stock option awards using the Black-Scholes option pricing model, which uses the assumptions noted in the tables below, including the risk-free interest rate, expected term, share price volatility, dividend yield and forfeiture rate. The risk-free interest rate is based upon the U.S. Treasury yield curve in effect at the time of grant, with a term that approximates the expected life of the option. For stock options issued in 2024 and 2023 that qualify as “plain vanilla” stock options, the expected term is based on the simplified method. The Company has a limited history of stock option exercises, which does not provide a reasonable basis for the Company to estimate the expected term of employee and non-employee stock options. For all other stock options, the Company estimates the expected life using judgment based on the anticipated research and development milestones of the Company’s clinical projects and behavior of the Company’s employees and non-employees. The expected life of non-employee options is the contractual life of the option.

Employee Stock Options

During the years ended December 31, 2024 and 2023, 30,000 and 57,500 total stock options to purchase shares of common stock were granted by the Company, respectively. The weighted average grant date fair value per option was $3.41 and $3.49, respectively. No employee stock options were exercised during the years ended December 31, 2024 and 2023. During the year ended December 31, 2024, 32,535 shares having a weighted average grant date fair value of $40.07 per option were forfeited. No employee stock options were forfeited or expired during the year ended December 31, 2023.

During the years ended December 31, 2024 and 2023, 53,750 and 33,333 total stock options vested, respectively, with total fair values of approximately $0.3 million in both periods. As of December 31, 2024, there was approximately $0.1 million of unrecognized share-based payments related to employee stock options that are expected to vest. The Company expects to recognize this expense over a weighted-average period of approximately 2.1 years.

Key assumptions used in the Black-Scholes option pricing model for options granted to employees during the years ending December 31, 2024 and 2023 are as follows:

The following is a summary of employee stock option activity for the years ended December 31, 2024 and 2023: