Amendment to Annual Report (Form 10-K/A)

This Amendment No. 1 (this "Amendment") amends the Annual Report on Form 10-K for the year ended December 31, 2025 of XBiotech, Inc. (the "Company"), filed with the Securities and Exchange Commission (the "SEC") on March 13, 2026 (the "Original Form 10-K"). The purpose of this Amendment is solely to amend Part III, Items 10 through 14 of the Original Form 10-K to include information previously omitted from the Original Form 10-K in reliance on General Instruction G(3) to Form 10-K which permits the above-referenced Items to be incorporated in the Annual Report on Form 10-K by reference from a definitive proxy statement, if such proxy statement is filed no later than 120 days after December 31, 2025. At this time, the Company is filing this Amendment to include Part III information in our Annual Report on Form 10-K because we do not intend to file a definitive proxy statement within 120 days of December 31, 2025. Accordingly, Part III of the Original Form 10-K is hereby amended and restated as set forth herein. The information included herein as required by Part III, Items 10 through 14 of Form 10-K is more limited than what is required to be included in the definitive proxy statement to be filed in connection with our annual meeting of stockholders. Accordingly, the definitive proxy statement to be filed at a later date will include additional information related to the topics herein and additional information not required by Part III, Items 10 through 14 of Form 10-K.

The reference on the cover page of the Original Form 10-K to the incorporation by reference of our definitive proxy statement into Part III of the Original Form 10-K is hereby deleted.

Except as stated herein, this Amendment does not reflect events occurring after the filing of the Original Form 10-K and no attempt has been made in this Amendment to modify or update other disclosures as presented in the Original Form 10-K.