Earlier quoted context omitted.
> Valve aren't really known for supporting their engines very well beyond their own internal needs They don't need to. S&box uses a fork of Source 2 that is maintained by Facepunch, with Valve's upstream changes merged in as needed.
Oh right, that's more reassuring. I guess you'd still have to cut a deal with Valve to use FPs fork commercially though? Which is a wildcard since the licensing terms aren't public as far as I can tell.
https://sbox.game/dev/doc/systems/game-exporting/ (bottom of page)