It looks like Pro can use argon in the Gemini app, but not in antigravity:
https://one.google.com/about/google-ai-plans/?icid=microsite...
Im on pro, installed gemini app, tried argon 4, keeps failing with 404, resource now found. Switched to gemini-3.8-flash in same session... worked.
It seems to be rolling out gradually.. not available at once to everyone.
Why the hell would I care about it on my phone? Jebus, Google is bad at products.