Director — Thomas J. Webb: Two directors are retiring from the board in accordance with the company's standard retirement policy, which is a routine governance event rather than a sudden executive loss.

Results of Operations and Financial Condition On August 3, 2026 Otter Tail Corporation issued a press release announcing its consolidated financial results for the second quarter of 2026. A copy of the press release is furnished herewith as Exhibit 99.1. The information in this Item 2.02 (including Exhibit 99.1 attached hereto) shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed incorporated by reference in any filing under the…

Entry into a Material Definitive Agreement. As previously reported, in 2024, putative federal class action lawsuits alleging violations of the antitrust laws were filed against Otter Tail Corporation and two subsidiaries (together, the “Company”), along with more than twenty other PVC pipe manufacturers. The actions were later consolidated as In re: PVC Pipe Antitrust Litigation (Case No. 1:24-cv-07639) in the United States District Court for the Northern District of Illinois (the “PVC Pipe A…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. As previously reported in a Form 8-K filed by Otter Tail Corporation on March 23, 2026 (the “March 8-K”), Otter Tail Power Company ("OTP”), a wholly owned subsidiary of Otter Tail Corporation, entered into a Note Purchase Agreement (the “Note Purchase Agreement”) on March 19, 2026, with the purchasers named therein (the “Purchasers”), pursuant to which OTP agreed to issue to the…

Entry into a Material Definitive Agreement. As previously reported, in 2024, putative federal class action lawsuits alleging violations of the antitrust laws were filed against Otter Tail Corporation and two subsidiaries (together, the “Company”), along with more than twenty other PVC pipe manufacturers. The actions were later consolidated as In re: PVC Pipe Antitrust Litigation (Case No. 1:24-cv-07639) in the United States District Court for the Northern District of Illinois (the “PVC Pipe A…

Results of Operations and Financial Condition On May 4, 2026 Otter Tail Corporation issued a press release announcing its consolidated financial results for the first quarter of 2026. A copy of the press release is furnished herewith as Exhibit 99.1. The information in this Item 2.02 (including Exhibit 99.1 attached hereto) shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed incorporated by reference in any filing under the Sec…

President — Tim Rogelstad: Tim Rogelstad was promoted to President, while Charles MacFarlane remains as CEO.

Entry into a Material Definitive Agreement On March 19, 2026, Otter Tail Power Company (the “Company”), a wholly owned subsidiary of Otter Tail Corporation (“OTC”), entered into a Note Purchase Agreement (the “Note Purchase Agreement”) with the purchasers named therein (the “Purchasers”), pursuant to which the Company issued to the Purchasers, in a private placement transaction, $170,000,000 aggregate principal amount of the Company’s senior unsecured notes consisting of $100,000,000 in aggre…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant The information contained in

Results of Operations and Financial Condition On February 16, 2026 Otter Tail Corporation issued a press release announcing its consolidated financial results for the quarter and year ended December 31, 2025, and its earnings guidance for 2026. A copy of the press release is furnished herewith as Exhibit 99.1. The information in this Item 2.02 (including Exhibit 99.1 attached hereto) shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be…

Director — Steven L. Fritze: The filing discloses a routine director retirement due to age policy with the simultaneous appointment of two qualified successors, representing an orderly succession rather than a sudden loss of leadership.

Results of Operations and Financial Condition On November 3, 2025 Otter Tail Corporation issued a press release announcing its consolidated financial results for the third quarter of 2025. A copy of the press release is furnished herewith as Exhibit 99.1. The information in this Item 2.02 (including Exhibit 99.1 attached hereto) shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed incorporated by reference in any filing under th…

Results of Operations and Financial Condition On August 4, 2025 Otter Tail Corporation issued a press release announcing its consolidated financial results for the second quarter of 2025. A copy of the press release is furnished herewith as Exhibit 99.1. The information in this Item 2.02 (including Exhibit 99.1 attached hereto) shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed incorporated by reference in any filing under the…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. As previously reported in a Form 8-K filed by Otter Tail Corporation on March 31, 2025 (the “March 8-K”), Otter Tail Power Company ("OTP”), a wholly owned subsidiary of Otter Tail Corporation, entered into a Note Purchase Agreement (the “Note Purchase Agreement”) on March 27, 2025, with the purchasers named therein (the “Purchasers”), pursuant to which OTP agreed to issue to the…

Results of Operations and Financial Condition On May 5, 2025 Otter Tail Corporation issued a press release announcing its consolidated financial results for the first quarter of 2025. A copy of the press release is furnished herewith as Exhibit 99.1. The information in this Item 2.02 (including Exhibit 99.1 attached hereto) shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed incorporated by reference in any filing under the Sec…

Entry into a Material Definitive Agreement On March 27, 2025, Otter Tail Power Company (the “Company”), a wholly owned subsidiary of Otter Tail Corporation (“OTC”), entered into a Note Purchase Agreement (the “Note Purchase Agreement”) with the purchasers named therein (the “Purchasers”), pursuant to which the Company issued to the Purchasers, in a private placement transaction, $100,000,000 aggregate principal amount of the Company’s senior unsecured notes consisting of $50,000,000 in aggreg…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant The information contained in

Results of Operations and Financial Condition On February 17, 2025 Otter Tail Corporation issued a press release announcing its consolidated financial results for the year ended December 31, 2024, and its earnings guidance for 2025. A copy of the press release is furnished herewith as Exhibit 99.1. The information in this Item 2.02 (including Exhibit 99.1 attached hereto) shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed inco…

Other Events North Dakota Rate Case Settlement On December 30, 2024, the North Dakota Public Service Commission (NDPSC) approved a settlement agreement between Otter Tail Power Company (OTP), a wholly owned subsidiary of Otter Tail Corporation, and certain interested parties in OTP’s general rate increase request originally filed on November 2, 2023. Per the terms of the settlement agreement, OTP will receive a $13.1 million, or 6.18%, net increase in annual base rate revenue. The net increas…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant The information contained in

Entry Into A Material Definitive Agreement Otter Tail Corporation Amended and Restated Credit Agreement On December 11, 2024, Otter Tail Corporation (the “Company”) entered into a Sixth Amended and Restated Credit Agreement (the “Otter Tail Credit Agreement”) with certain banks as named therein, and led by U.S. Bank National Association (“U.S. Bank”), as administrative agent. The agreement provides for an unsecured revolving credit facility with a $170 million line of credit the Company can d…

Results of Operations and Financial Condition On November 4, 2024 Otter Tail Corporation issued a press release announcing its consolidated financial results for the third quarter of 2024. A copy of the press release is furnished herewith as Exhibit 99.1. The information in this Item 2.02 (including Exhibit 99.1 attached hereto) shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed incorporated by reference in any filing under th…

Results of Operations and Financial Condition On August 5, 2024 Otter Tail Corporation issued a press release announcing its consolidated financial results for the second quarter of 2024. A copy of the press release is furnished herewith as Exhibit 99.1. The information in this Item 2.02 (including Exhibit 99.1 attached hereto) shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed incorporated by reference in any filing under the…

Other Events Resource Planning On May 30, 2024, the Minnesota Public Utilities Commission (MPUC) approved Otter Tail Power Company’s 2022 to 2036 Integrated Resource Plan. Otter Tail Power Company is a wholly-owned subsidiary of Otter Tail Corporation. Consistent with MPUC practice, the decision was made during deliberations by oral vote and is subject to the issuance of a final written order. The MPUC: – Directed Otter Tail Power to procure the following generation resources, subject to addi…

Results of Operations and Financial Condition On May 6, 2024 Otter Tail Corporation issued a press release announcing its consolidated financial results for the first quarter of 2024. A copy of the press release is furnished herewith as Exhibit 99.1. The information in this Item 2.02 (including Exhibit 99.1 attached hereto) shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, nor shall it be deemed incorporated by reference in any filing under the Sec…