There&#x27;s a public RFC, but it&#x27;s by no means usable as a bitstream spec.
There&#x27;s an official text document describing the bitstream format (several hundreds pages), but it&#x27;s under NDA.
We use it at work, and getting an updated version is far more trouble than downloading a file on a public server.
The document in itself is nearly worthless, though, as it&#x27;s far from complete. In the end, you still need to dig into libvpx to understand how things work.