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UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON , D.C. 20549 FORM 10 - K ( Mark One ) ☑ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended September 30 , 2021 Or ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-35570 SONNET BIOTHERAPEUTICS HOLDINGS , INC . ( Exact name of registrant as specified in its charter ) Delaware ( State or other jurisdiction of incorporation or organization ) 20-2932652 ( I.R.S. Employer Identification No. ) 100 Overlook Center , Suite 102 Princeton , NJ 08540 ( 609 ) 375-2227 ( Address , including zip code , and telephone number , including area code , of registrant's principal executive offices ) Title of each class Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol SONN Name of each exchange on which registered The Nasdaq Stock Market LLC Common Stock , $ 0.0001 par value per share Securities registered pursuant to Section 12 ( g ) of the Act : None Indicate by check if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes No Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes : □ No : < Indicate by check mark if the registrant : ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes : > No : □ Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes : No : □ Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of “ large accelerated filer , ” “ accelerated filer , ” “ smaller reporting company , " and " emerging growth company ” in Rule 12b - 2 of the Exchange Act .