X0202 SCHEDULE 13D/A 0000921895-26-001441 0001633362 XXXXXXXX LIVE 1 Common Stock 10/20/2026 false 0001315257 50060P106 Koppers Holdings Inc.

436 SEVENTH AVENUE PITTSBURGH PA 15219

JEFFREY JACOBOWITZ 212-448-7400 SIMCOE CAPITAL MANAGEMENT, LLC 540 Madison Avenue, 27th Floor New York NY 10022 STEVE WOLOSKY & IAN ENGORON 212-451-2300 OLSHAN FROME WOLOSKY LLP 1325 Avenue of the Americas New York NY 10019 0001633362 N Simcoe Capital Management, LLC AF N DE 1063279.00 0.00 1063279.00 0.00 1063279.00 N 5.6 OO 0001220336 N SIMCOE PARTNERS L P WC N DE 873494.00 0.00 873494.00 0.00 873494.00 N 4.6 PN 0001758330 N Simcoe Select, LP WC N DE 154000.00 0.00 154000.00 0.00 154000.00 N 0.8 PN Y SIMCOE MANAGEMENT COMPANY, LLC AF N DE 1027494.00 0.00 1027494.00 0.00 1027494.00 N 5.4 OO 0001538519 N SDR Partners, LLC WC N DE 35785.00 0.00 35785.00 0.00 35785.00 N 0.2 OO 0001450714 N Jacobowitz Jeffrey AF N X1 1063279.00 0.00 1063279.00 0.00 1063279.00 N 5.6 IN Common Stock Koppers Holdings Inc. 436 SEVENTH AVENUE PITTSBURGH PA 15219 Item 3 is hereby amended and restated to read as follows: The shares of the Issuer's Common Stock (the "Shares") purchased by each of Simcoe Partners, Simcoe Select and SDR Partners were purchased with working capital (which may, at any given time, include margin loans made by brokerage firms in the ordinary course of business) in open market purchases. The aggregate purchase price of the 873,494 Shares directly owned by Simcoe Partners is approximately $24,977,523, including brokerage commissions. The aggregate purchase price of the 154,000 Shares directly owned by Simcoe Select is approximately $6,544,634, including brokerage commissions. The aggregate purchase price of the 35,785 Shares directly owned by SDR Partners is approximately $1,213,593, including brokerage commissions. Item 5(a) is hereby amended and restated to read as follows: The aggregate percentage of Shares reported owned by each person named herein is based on 18,911,568 Shares outstanding, as of July 31, 2026, which is the total number of Shares outstanding as reported in the Issuer's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on August 6, 2026. A. Simcoe Partners As of the date hereof, Simcoe Partners directly owned 873,494 Shares. Percentage: approximately 4.6% B. Simcoe Select As of the date hereof, Simcoe Select directly owned 154,000 Shares. Percentage: less than 1% C. Simcoe Management Simcoe Management, as the general partner of Simcoe Partners and Simcoe Select, may be deemed the beneficial owner of the (i) 873,494 Shares owned by Simcoe Partners and (ii) 154,000 Shares owned by Simcoe Select. Percentage: approximately 5.4% D. SDR Partners As of the date hereof, SDR Partners directly owned 35,785 Shares. Percentage: less than 1% E. Simcoe Capital Simcoe Capital, as the investment manager to each of Simcoe Partners, Simcoe Select and SDR Partners, may be deemed the beneficial owner of the (i) 873,494 Shares owned by Simcoe Partners, (ii) 154,000 Shares owned by Simcoe Select and (iii) 35,785 Shares owned by SDR Partners. Percentage: approximately 5.6% F. Mr. Jacobowitz Mr. Jacobowitz, as Managing Member of each of Simcoe Management and Simcoe Capital, may be deemed the beneficial owner of the (i) 873,494 Shares owned by Simcoe Partners, (ii) 154,000 Shares owned by Simcoe Select and (iii) 35,785 Shares owned by SDR Partners. Percentage: approximately 5.6% Item 5(b) is hereby amended and restated to read as follows: A. Simcoe Partners 1. Sole power to vote or direct vote: 873,494 2. Shared power to vote or direct vote: 0 3. Sole power to dispose or direct the disposition: 873,494 4. Shared power to dispose or direct the disposition: 0 B. Simcoe Select 1. Sole power to vote or direct vote: 154,000 2. Shared power to vote or direct vote: 0 3. Sole power to dispose or direct the disposition: 154,000 4. Shared power to dispose or direct the disposition: 0 C. Simcoe Management 1. Sole power to vote or direct vote: 1,027,494 2. Shared power to vote or direct vote: 0 3. Sole power to dispose or direct the disposition: 1,027,494 4. Shared power to dispose or direct the disposition: 0 D. SDR Partners 1. Sole power to vote or direct vote: 35,785 2. Shared power to vote or direct vote: 0 3. Sole power to dispose or direct the disposition: 35,785 4. Shared power to dispose or direct the disposition: 0 E. Simcoe Capital 1. Sole power to vote or direct vote: 1,063,279 2. Shared power to vote or direct vote: 0 3. Sole power to dispose or direct the disposition: 1,063,279 4. Shared power to dispose or direct the disposition: 0 F. Mr. Jacobowitz 1. Sole power to vote or direct vote: 1,063,279 2. Shared power to vote or direct vote: 0 3. Sole power to dispose or direct the disposition: 1,063,279 4. Shared power to dispose or direct the disposition: 0 Each Reporting Person, as a member of a "group" with the other Reporting Persons for the purposes of Section 13(d)(3) of the Securities Exchange Act of 1934, as amended, may be deemed the beneficial owner of the Shares directly owned by the other Reporting Persons. Each Reporting Person disclaims beneficial ownership of such Shares except to the extent of his or its pecuniary interest therein. Item 5(c) is hereby amended and restated to read as follows: The transactions in the Shares by the Reporting Persons during the past 60 days are set forth in Exhibit 1 and incorporated herein by reference. Item 7 is hereby amended to add the following exhibit: 1 - Transactions in Securities Simcoe Capital Management, LLC /s/ Jeffrey Jacobowitz 10/22/2026 SIMCOE PARTNERS L P /s/ Jeffrey Jacobowitz 10/22/2026 Simcoe Select, LP /s/ Jeffrey Jacobowitz 10/22/2026 SIMCOE MANAGEMENT COMPANY, LLC /s/ Jeffrey Jacobowitz 10/22/2026 SDR Partners, LLC /s/ Jeffrey Jacobowitz 10/22/2026 Jacobowitz Jeffrey /s/ Jeffrey Jacobowitz 10/22/2026