BioAtla Inc 美股招股说明书（2026年3月20日版）

Filed Pursuant to Rule 424(b)(2)Registration No. 333-269148 PROSPECTUS SUPPLEMENT NO. 3 (To Prospectus dated January17, 2023 andProspectus Supplement dated November 20, 2025) 842,440 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated November 20, 2025 and the base prospectus datedJanuary 17, 2023 (as supplemented from time to time, the “Prospectus”), we are offering 842,440 shares of our common stock to YA IIPN, Ltd., a Cayman Islands exempt limited company (“Yorkville”), at a price of approximately $0.179 per share, pursuant to ourpreviously announced Standby Equity Purchase Agreement with Yorkville dated November 20, 2025 (the “SEPA”). These shares arebeing issued as part of the commitment by Yorkville to purchase from time to time shares of our common stock pursuant to the SEPA. In addition to our issuance of our shares to Yorkville pursuant to the SEPA, this Prospectus also covers the resale of these sharesby Yorkville to the public. Although we have been advised by Yorkville, and Yorkville represents in the SEPA, that Yorkville ispurchasing the shares for its own account, for investment purposes in which it takes investment risk (including, without limitation, therisk of loss), and without any view or intention to distribute such shares in violation of the Securities Act of 1933, as amended (the“Securities Act”), or any other applicable securities laws, the Securities and Exchange Commission (the “SEC”) may take the positionthat Yorkville may be deemed an “underwriter” within the meaning of Section 2(a)(11) of the Securities Act and any profits on the Our common stock is listed on The Nasdaq Capital Market under the symbol “BCAB.” The last reported sale price of ourcommon stock on The Nasdaq Capital Market on March 19, 2026 was $0.16 per share. We are a “smaller reporting company” under Investing in our securities involves a high degree of risk. You should carefully consider the risks described under theheading “Risk Factors” beginning on pageS-8of the prospectus supplement dated November 20, 2025 and the documents Neither the SEC nor any state securities commission has approved or disapproved of these securities or determined if thisprospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a Neither we nor Yorkville have authorized anyone to provide you with any information other than the informationcontained in or incorporated by reference in this prospectus supplement, or the prospectus supplement dated November 20,2025 and base prospectus dated January 17, 2023 and in the documents incorporated by reference herein and therein. We andYorkville take no responsibility for, and can provide no assurance as to the reliability of, any other information that others maygive you. We are not making an offer of these securities in any state or jurisdiction where the offer is not permitted. You should Prospectus Supplement dated March 19, 2026 WHERE YOU CAN FIND ADDITIONAL INFORMATION We file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings areavailable to the public at the SEC’s website at www.sec.gov. Copies of certain information filed by us with the SEC are also availableon our website at www.bioatla.com. Information accessible on or through our website is not a part of this prospectus supplement. This prospectus supplement and the prospectus supplement dated November 20, 2025 and base prospectus dated January 17, 2023are part of a registration statement on Form S-3 that we filed with the SEC and does not contain all of the information in theregistration statement. You should review the information and exhibits in the registration statement for further information on us andthe securities that we are offering. The SEPA is filed as an exhibit to the Company’s Current Report on Form 8-K filed with the SECon November 21, 2025 and incorporated in this prospectus supplement by reference. Statements in this prospectus supplement about