Amendments to Bylaws (Form 8-K)

On May 12, 2026, the Board of Directors of International Bancshares Corporation ("IBC") approved and adopted the Third Amended and Restated By-Laws of IBC (the "By-Laws") to remove the requirement that a shareholder or group of shareholders may not institute or maintain a derivative proceeding unless that shareholder or group of shareholders beneficially own three percent of IBC's issued and outstanding common stock, par value $1.00 per share, at the time such derivative proceeding is instituted.

In addition, the By-Laws were amended to eliminate the exclusive forum clause which previously designated the Texas Business Court located in the Fourth Business Court Division or, if such court lacked jurisdiction the United States District Court for the Southern District of Texas, or if such court lacked jurisdiction the state district court of Webb County as the sole and exclusive forum for any filing or claim unless agreed to otherwise. The amendments to the By-Laws no longer require that each shareholder, director, and officer irrevocably and unconditionally waive any right they may have to a trial by jury in any legal action, proceeding, cause of action, or counterclaim concerning any internal entity claim and in any other claim, action, or proceeding against IBC, to the fullest extent permitted by applicable law.

The By-Laws became effective on May 12, 2026.

A copy of the By-Laws is attached as Exhibit 3.1, to this Current Report on Form 8-K, and is incorporated herein by reference in its entirety.