When you use Free Account, it starts with GPT-4o model as default.
After 10 prompts, it turns to GPT-4o mini model.
Approximately after 4 hours and 35 minutes you can use another 10 prompts again with GPT-4o model.
It shows tools.
Now, it shows on Free Account as “Browsing”
Because it is FREE account, It uses “Browse” tool instead of “Web Search” tool.
Although Free Account uses GPT-4o model, it uses “Browse” tool that is used also on GPT-4.
OpenAI declared here about “Web Search” tool for Free users:
It will roll out to all Free users over the coming months.
Big question is: “WHEN?” 
This is which tool is used by Free Account to search:
You can try models copy paste link to your browser, but, default_model_slug is “auto” as you can see above image in latest third line, so you cannot switch.