Just like with the Steam Deck, Valve's more powerful home console will be verifying which games it can feasibly put on its Steam Machine platform. These verification rules will be the same as those on the Steam Deck, with games having to run at 1080p, 30fps in order to be verified.
While 1080p, 30fps might not sound like great performance for a console that's meant to be 6x more powerful than a Steam Deck, as PC Gamer notes this is just the minimum Steam Machine verification measures. Moreover, developers trying to get their games on the GabeCube will only have to deal with the Steam Deck's input requirements, and won't hit any targets for display resolution or legibility, as you'll be playing the Steam Machine ideally on a screen much larger than a Steam Deck's display.
Looking over at the Steam Frame, Valve doesn't have a verification process there, as it's mainly a streaming device from your home PC. If your rig can run the game, Steam Frame can handle it, too, is the idea. More generally, Valve also had some aspects developers should focus on when making games for SteamOS, namely offline modes support, the optimisation of lower specs, and acknowledgement of more controller users coming to PC all the time.