Allegedly it's already available in stealth mode if you choose the "canvas" tool and 2.5. I don't know how true that is, but it is indeed pumping out some really impressive one shot code

Edit: Now that I have access to Gemini 3 preview, I've compared the results of the same one shot prompts on the gemini app's 2.5 canvas vs 3 AI studio and they're very similar. I think the rumor of a stealth launch might be true.