Sec Form 4 Filing - ROBERTSON GREG @ Business First Bancshares, Inc. - 2026-03-01

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person ROBERTSON GREG 2. Issuer Name and Ticker or Trading Symbol Business First Bancshares, Inc. [ BFST] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) EVP and CFO (Last) (First) (Middle) 500 LAUREL STREET, SUITE 101 3. Date of Earliest Transaction (MM/DD/YY) 03/01/2026 (Street) BATON ROUGE, LA70801 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price COMMON STOCK 03/01/2026 M 1,926 A 71,092 ( 1 ) D COMMON STOCK 03/01/2026 F 527 D $ 27.3 70,565 ( 1 ) D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Restricted Stock Units ( 2 ) 03/01/2026 M 1,926 ( 2 ) ( 2 ) Common Stock 1,926 ( 2 ) 7,634 D Restricted Stock Units $ 0 03/02/2026 A 1,148 ( 3 ) ( 3 ) ( 3 ) Common Stock 1,148 ( 3 ) 8,782 D Restricted Stock Units $ 0 03/02/2026 A 4,592 ( 4 ) ( 4 ) ( 4 ) Common Stock 4,592 ( 4 ) 13,374 ( 5 ) D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other ROBERTSON GREG 500 LAUREL STREET, SUITE 101 BATON ROUGE, LA70801 EVP and CFO Signatures /s/ Heather Roemer, as attorney-in-fact for Gregory Robertson 03/03/2026 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Includes 3,776 shares of unvested restricted stock granted on February 1, 2024, which will vest on March 31, 2026. Under the terms of the relevant restricted stock grants, the reported shares of unvested restricted stock are subject to forfeiture upon the occurrence of certain events. ( 2 )The reporting person received an award of 5,838 time-based restricted stock units granted on March 1, 2025, vesting in three substantially equal installments on the first, second, and third anniversary of the issuance date. ( 3 )Reflects the grant of 1,148 time-based restricted stock units granted to the reporting person on March 2, 2026, of which 382 shares will vest on March 2, 2027, 382 shares will vest on March 2, 2028, and the remaining 384 shares will vest on March 2, 2029. Each time-based restricted stock unit is economically equivalent to one share of common stock of the issuer. ( 4 )Reflects the grant of 4,592 time-based restricted stock units granted to the reporting person on March 2, 2026, of which 1,530 shares will vest on March 2, 2027, 1,530 shares will vest on March 2, 2028, and the remaining 1,532 shares will vest on March 2, 2029. Each time-based restricted stock unit is economically equivalent to one share of common stock of the issuer. The reporting person has irrevocably elected to defer the reported securities under the b1BANK Deferred Compensation Plan (the "Deferred Compensation Plan"). In accordance with the Deferred Compensation Plan, the reporting person will receive a lump sum cash distribution in an amount equal to the vested securities deferred under the Deferred Compensation Plan, plus any earnings or losses attributable thereto, on the first business day following the month in which the reporting person's separation of service, death, or disability occurs. ( 5 )Includes: (a) 3,722 time-based restricted stock units granted to the reporting person on December 12, 2024, which will vest in two substantially equal installments on the second and third anniversary of the issuance date; (b) 3,912 time-based restricted stock units granted to the reporting person on March 1, 2025, which will vest in two substantially equal installments on the second and third anniversary of the issuance date; (c) 1,148 time-based restricted stock units granted to the reporting person on March 2, 2026, which will vest in three substantially equal installments on the first, second, and third anniversary of the issuance date; and (d) 4,592 time-based restricted stock units granted to the reporting person on March 2, 2026, which will vest in three substantially equal installments on the first, second, and third anniversary of the issuance date.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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