Model Identity Discrepancy and Performance Issues - Possible Billing Mismatch

Bug Description

I'm experiencing significant issues with model consistency and performance that started today.

1. The model is identifying itself as "Claude 3.5 Sonnet (October 2024 version)" (Max $200 user here)
2. However, system prompts visible in the conversation reference "Opus 4" and model ID "claude-opus-4-20250514"
3. I'm paying for Claude 4 access but appear to be receiving Claude Sonnet 3.5 responses, not even 3.7
4. Performance has dramatically degraded - the model is making repetitive mistakes and behaving very differently compared to this morning

Evidence:

• Model self-identifies as Claude 3.5 Sonnet
• System messages reference Opus 4
• Significant behavior changes and error loops started suddenly

<img width="2138" height="224" alt="Image" src="https://github.com/user-attachments/assets/e448b8f7-0693-465f-96a3-b5ce41da3266" />

Request:
Please investigate whether there's a billing/access mismatch and ensure I'm receiving the correct model tier I'm paying for.

Environment Info

• Platform: darwin
• Terminal: vscode
• Version: 1.0.67
• Feedback ID: a9640454-45e5-4e3d-a766-4ca505802a13