Sec Form 4 Filing - Curran Timothy Joseph @ FOSTER L B CO - 2026-06-01

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 Curran Timothy Joseph 2. Issuer Name and Ticker or Trading Symbol FOSTER L B CO [ FSTR] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Controller and PAO (Last) (First) (Middle) C/O L.B. FOSTER COMPANY, 415 HOLIDAY DRIVE, SUITE 100 3. Date of Earliest Transaction (MM/DD/YY) 06/01/2026 (Street) PITTSBURGH, PA15220 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 06/01/2026 A 295 ( 1 ) A $ 0 9,090 ( 2 ) ( 3 ) 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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Curran Timothy Joseph C/O L.B. FOSTER COMPANY 415 HOLIDAY DRIVE, SUITE 100 PITTSBURGH, PA15220 Controller and PAO Signatures /s/ Timothy J. Curran by Maribel Castro, attorney-in-fact 06/03/2026 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Award of 295 restricted stock units (RSUs) which are settled in stock upon vesting and generally will vest ratably over a three-year period on the first, second, and third anniversary of the date of the grant. ( 2 )Includes 255 Performance Restricted Stock Units earned under the 2025-2027 Long Term Incentive Plan granted on 5/22/2025; those 255 Performance Restricted Stock Units will settle at the end of the performance period on December 31, 2027, upon certification by the Compensation Committee. ( 3 )Includes 966 Performance Restricted Stock Units earned under the 2024-2026 Long Term Incentive Plan granted on 5/23/2024; those 966 Performance Restricted Stock Units will settle at the end of the performance period on December 31, 2026, upon certification of the Compensation Committee.

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).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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