It's the size of a SHA256 digest but it doesn't match the checksum of the firmware file I uploaded.
I don't have any reason to think there's anything wrong with it, and verify-file flash ADTRAN_TA900E3A-R13-7-1-E.biz reports success and valid, but I seem to be missing it if there's a way to confirm the checksum of the firmware loaded/running on my 908e matches the verification hash on the software download web page.