Thanks for the detailed logs - they’re super helpful. This looks like a provider-side issue specifically on the Sonnet 4 route in Reasoning/Max modes (a similar problem recently occurred with Sonnet 4.5 and was fixed on the backend: Reproducible - Unable to reach model provider - Sonnet 4.5).
We need a few more data points to escalate this to the engineers:
- 2-3 fresh Request IDs for failed Sonnet 4 Reasoning/Max requests + exact UTC time of each
- Are you using your own API key? If yes - which provider?
- Tests on modes:
- Sonnet 4.5 Reasoning (without Max) - works or fails?
- Sonnet 4.5 Max (without Reasoning) - works or fails?
- Test with a different connection (e.g., mobile hotspot) - results and ISP
- Confirm you restarted Cursor and tried a new chat after switching “Disable HTTP/2”
Temporary workaround: use Sonnet 4.5, or GPT-5 - you noted they work. Send the above info, and we’ll escalate routing checks with the provider immediately.