Anthropic very recently made it so you get like 3 free messages at a time with sonnet 4.6. Gemini 3.5 flash just dropped today, and you can use it all day long for free (you only have to pay for the pro versions which is still on 3.1). And I would say 3.5 flash is better than sonnet 4.6 anyway. Have been using it since it dropped like an hour ago. It's very good. Its writing is the most human-like of any model I have seen so far.