X0306 4 2023-02-09 0 0001826892 BioAtla, Inc. BCAB 0001835116 Sievers Eric C/O BIOATLA, INC. 11085 TORREYANA ROAD SAN DIEGO CA 92121 0 1 0 0 Chief Medical Officer Common Stock 2023-02-28 4 F 0 554 2.98 D 92746 D Employee Stock Option (right to buy) 3.95 2023-02-09 4 A 0 240000 0.00 A 2033-02-09 Common Stock 240000 240000 D This transaction is not a sale of shares by the Reporting Person. Instead, this represents shares that have been withheld by the Issuer to satisfy its income tax and withholding and remittance obligations in connection with the vesting and net settlement of previously reported restricted stock units. The option vests over a period of four years, with 25% of the shares underlying the option vesting on the first anniversary of the date of grant, and the remainder vesting in 36 substantially equal monthly installments thereafter, subject to the reporting person's continued service to the company through the applicable vesting dates. /s/ Christian Vasquez, as Attorney-in-Fact for Eric Sievers 2023-03-01