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TABLE OF CONTENTS ( Mark One ) ý SECURITIES AND EXCHANGE COMMISSION WASHINGTON , DC 20549 UNITED STATES 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 Delaware ( State or Other Jurisdiction of Incorporation or Organization ) Form 10 - K Commission file number : 814-00794 GOLUB CAPITAL BDC , INC . ( Exact Name of Registrant as Specified in its Charter ) 200 Park Avenue , 25th Floor , New York , NY ( Address of Principal Executive Offices ) Title of each class Common Stock , par value $ 0.001 per share 27-2326940 ( I.R.S. Employer Identification No. ) ( 212 ) 750-6060 ( Registrant's Telephone Number , Including Area Code ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol GBDC 10166 ( Zip Code ) 1 Name of each exchange on which registered The Nasdaq Global Select Market Securities registered pursuant to Section 12 ( g ) of the Act : None Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes o No ý Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15 ( d ) of the Act . Yes o No ý Indicate by check mark whether 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 ý No o 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 ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes o No ý Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer or a smaller reporting company . See definitions of " large accelerated filer " , " accelerated filer " and " smaller reporting company " in Rule 12b - 2 of