So the ModRetro × OpenAI collab only requires a free plugin for you to develop GBC games in the Codex the app

But play-testing on a real Chromatic requires a firmware update and API key that came in the box with the DevDay devices

https://support.modretro.com/en_us/chromatic-devday-edition-...

I just tried it and prompted a GBC version of YOYOZO, my GOTY game. Wild times.