What you’re seeing isn’t the main Auto request running Sonnet 5, it’s the Explore step. When you plan on Auto, the agent can spin up a short Explore subagent to research your codebase first, and subagents choose their own model instead of following the Auto picker. That research subagent ran Sonnet 5, which is why the usage showed up even though the picker still reads Auto.
This is a rough edge we’ve seen reported, and we’re improving how subagents pick models so they don’t quietly land on a premium one. For now you can control it directly: in Cursor Settings → Models, set the Explore subagent model to a lighter option (a fast Composer model is a good default) so the research step stops using Sonnet 5.
Your main Auto selection is working as expected here; it’s just that the subagent step carries its own model. Let me know if changing that setting doesn’t stick and I’ll dig in further.
