github coilot agent

[karamur]

🏷️ Discussion Type

Bug

💬 Feature/Topic Area

Copilot in GitHub

Body

Bug Report: Invalid 'signature' in 'thinking' block error with Claude models

Description:
When using GitHub Copilot agent mode with Claude Sonnet 4.5 or Claude Opus 4.5, the following error occurs:

Invalid 'signature' in 'thinking' block — invalid_request_body (HTTP 400 Bad Request)

Steps to Reproduce:

1. Open GitHub Copilot in Visual Studio
2. Select Claude Opus 4.5 or Claude Sonnet 4.5 as the model
3. Send any message in agent mode
4. Error appears immediately

Expected Behavior:
The model should respond normally without errors.

Actual Behavior:
HTTP 400 error with message: {"error":{"message":"messages.3.content.0: Invalid 'signature' in 'thinking' block","code":"invalid_request_body"}}

Environment:

• IDE: Microsoft Visual Studio
• Client: Microsoft.VisualStudio.Conversations.Chat.HelpWindow
• Correlation ID: 398882bc-5f38-4b52-ab2a-e8b510f1bb60

Additional Notes:
This appears to be a compatibility issue between GitHub Copilot and Anthropic's extended thinking feature in Claude models.

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