It is an entirely free model, but it is also the model that most users (even paid) interact with until the router pushes the thinking.
Correct. I have the $20/month plan and I just checked, the default is 5.3-instant. I can manually switch it to Thinking is 5.5. I also have it set to auto-switch.
Good point. I feel like this does a disservice to ChatGPT -- IIRC even the free tier of Claude points you to Sonnet 4.6 by default, which is magnitudes better than 5.3-instant which has been the default in ChatGPT.
Hence most users will immediately think Claude is smarter, even if their best models are on par.