On their roadmap (it's in the linked blog post https://code.visualstudio.com/blogs/2025/09/15/autoModelSele...):

> Let users on a free plan take advantage of the latest models through auto

It also describes how the auto selector works in more detail:

> When using auto model selection, VS Code uses a variable model multiplier based on the automatically selected model. If you are a paid user, auto applies a 10% request discount. For example, if auto selects Sonnet 4, it will be counted as 0.9x of a premium request; if auto selects GPT-5-mini, this counts as 0x because the model is included for paid users. You can see which model and model multiplier are used by hovering over the chat response.