Material Event (Form 8-K)

On October 1, 2026, Blue Bird Corporation (the "Company") filed with the Securities and Exchange Commission a prospectus supplement (the "Prospectus Supplement") to its automatic shelf registration statement on Form S-3 (File No. 333-284017) relating to the resale, from time to time, by the selling stockholder identified therein of up to 2,702,180 shares of the Company's common stock issuable upon the exchange, retraction or redemption, at the election of the selling stockholder, of non-voting exchangeable shares (the "Exchangeable Shares") of MB Exchangeco Inc., an indirect wholly owned Canadian subsidiary of the Company ("MB ExchangeCo"), or in connection with certain liquidation, dissolution, winding-up or insolvency events involving the Company or MB ExchangeCo. The Exchangeable Shares were issued by MB ExchangeCo in connection with the Company's acquisition, completed on April 1, 2026, of the 50% interest in the Company's Micro Bird joint venture enterprise held by the former joint venture partner.

This Current Report on Form 8-K is being filed solely for the purpose of filing the opinion of Smith, Gambrell & Russell, LLP relating to the validity of the Company's common stock offered by the Prospectus Supplement and the accompanying prospectus, which opinion is attached as Exhibit 5.1 hereto.