Subsequent Events	12 Months Ended
Dec. 31, 2025
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events The Company has evaluated subsequent events for potential recognition and disclosure through the filing date of this Form 10-K. Regulatory approval from the Office of the Comptroller of the Currency: On February 25, 2026, FirstSun and First Foundation announced receipt of regulatory approval from the Office of the Comptroller of the Currency to complete the merger of their respective bank subsidiaries, Sunflower Bank, N.A. and First Foundation Bank, as part of the previously announced merger between FirstSun and First Foundation. Completion of the merger remains subject to receipt of regulatory approval from the Board of Governors of the Federal Reserve System. FirstSun Special Meeting of Stockholders: FirstSun held a special meeting of stockholders on February 27, 2026 (the “FirstSun special meeting”). At the FirstSun special meeting, the following four proposals were considered: •Proposal 1: a proposal to adopt the Agreement and Plan of Merger, dated as of October 27, 2025, by and between FirstSun and First Foundation Inc. (“First Foundation”), as it may be amended from time to time (the “merger agreement”), under which First Foundation will merge with and into FirstSun, and to approve the consummation of the transactions contemplated thereby, including the issuance of shares of FirstSun common stock as merger consideration (the “FirstSun merger proposal”); •Proposal 2: a proposal to approve an amendment to FirstSun’s certificate of incorporation to increase the number of authorized shares of FirstSun common stock (the “FirstSun authorized common increase proposal”); •Proposal 3: a proposal to approve an amendment to FirstSun’s certificate of incorporation to create a class of non-voting common stock, to be available, among other things, for issuance to certain former First Foundation stockholders in connection with the merger (the “FirstSun non-voting common stock proposal”); and •Proposal 4: a proposal to adjourn the FirstSun special meeting, if necessary or appropriate, to permit further solicitation of proxies in favor of the FirstSun merger proposal, the FirstSun authorized common increase proposal or the FirstSun non-voting common stock proposal (the “FirstSun adjournment proposal”). Each proposal considered and voted on was approved by the requisite vote of FirstSun’s stockholders. The final voting results for the FirstSun merger proposal can be found in the 8-K filed with the SEC on February 27, 2026. Because a quorum was present at the special meeting and proposals 1, 2, and 3 each received the requisite vote needed for approval, a vote on the FirstSun adjournment proposal was withdrawn and not called. For more information on each of these proposals, see the definitive joint proxy statement/prospectus filed by FirstSun with the U.S. Securities and Exchange Commission (“SEC”) on January 15, 2026, as supplemented by the supplement to joint proxy statement/prospectus filed by FirstSun with the SEC on February 6, 2026.

On February 25, 2026, FirstSun and First Foundation announced receipt of regulatory approval from the Office of the Comptroller of the Currency to complete the merger of their respective bank subsidiaries, Sunflower Bank, N.A. and First Foundation Bank, as part of the previously announced merger between FirstSun and First Foundation.

FirstSun held a special meeting of stockholders on February 27, 2026 (the “FirstSun special meeting”). At the FirstSun special meeting, the following four proposals were considered:

•Proposal 1: a proposal to adopt the Agreement and Plan of Merger, dated as of October 27, 2025, by and between FirstSun and First Foundation Inc. (“First Foundation”), as it may be amended from time to time (the “merger agreement”), under which First Foundation will merge with and into FirstSun, and to approve the consummation of the transactions contemplated thereby, including the issuance of shares of FirstSun common stock as merger consideration (the “FirstSun merger proposal”);

•Proposal 2: a proposal to approve an amendment to FirstSun’s certificate of incorporation to increase the number of authorized shares of FirstSun common stock (the “FirstSun authorized common increase proposal”);

•Proposal 3: a proposal to approve an amendment to FirstSun’s certificate of incorporation to create a class of non-voting common stock, to be available, among other things, for issuance to certain former First Foundation stockholders in connection with the merger (the “FirstSun non-voting common stock proposal”); and

•Proposal 4: a proposal to adjourn the FirstSun special meeting, if necessary or appropriate, to permit further solicitation of proxies in favor of the FirstSun merger proposal, the FirstSun authorized common increase proposal or the FirstSun non-voting common stock proposal (the “FirstSun adjournment proposal”).

Each proposal considered and voted on was approved by the requisite vote of FirstSun’s stockholders. The final voting results for the FirstSun merger proposal can be found in the 8-K filed with the SEC on February 27, 2026. Because a quorum was present at the special meeting and proposals 1, 2, and 3 each received the requisite vote needed for approval, a vote on the FirstSun adjournment proposal was withdrawn and not called. For more information on each of these proposals, see the definitive joint proxy statement/prospectus filed by FirstSun with the U.S. Securities and Exchange Commission (“SEC”) on January 15, 2026, as supplemented by the supplement to joint proxy statement/prospectus filed by FirstSun with the SEC on February 6, 2026.