Flash and Pro models are moving to paid plans, free users will only get Flash-Lite. Flash-Lite is the same model used by the Android phone Gemini app and AI Overviews in Google Search, which is very poor at reasoning and makes many errors.

Personally, I've been using the free plan quite a lot and never hit a rate limit, but noticed the quality dropping. Pro was almost never available. Perhaps they aren't able to deliver a good quality Flash model to free users.