Copilot Chat Agent freezes VS Code during Replace String in File / Evaluating

[rodopoulos1]

• Copilot Chat Extension Version: 0.41 (2026-03-25)
• VS Code Version: 1.119.1
• OS Version: Windows
• Feature (e.g. agent/edit/ask mode): Agent mode / file editing
• Selected model (e.g. GPT 4.1, Claude 3.7 Sonnet): Claude Sonnet 4.6
• Logs: I could not collect logs through VS Code because the editor became completely unresponsive. I can attach logs from the VS Code logs folder if needed.

Steps to Reproduce:

1. Open any local project/workspace in VS Code with GitHub Copilot Chat enabled.
2. Start Copilot Chat in Agent mode using Claude Sonnet 4.6.
3. Ask the agent to inspect and edit multiple files in the workspace.
4. The agent reviews the files and starts applying changes.
5. Sometimes it gets stuck at "Evaluating" / "Replace String in File".
6. When this happens, VS Code becomes completely frozen and unresponsive.
7. Help → Report Issue cannot be used because the UI is frozen.
8. The only way to recover is to force close Code.exe manually.

Expected behavior:

Copilot Chat Agent should either complete the file edits or fail gracefully with an error message. It should not freeze the entire VS Code window.

Actual behavior:

Copilot Chat Agent sometimes gets stuck while applying file edits and freezes the entire VS Code editor. The UI becomes unusable and I have to force close VS Code.

This issue is intermittent. Sometimes opening a new Copilot Chat session makes it work normally again for a while. However, on some days, even a fresh new chat session freezes in the same way.

Additional information:

This does not appear to be a hardware limitation on my PC. The machine is high-end and normally handles heavy development workloads without issues. The freeze happens specifically while Copilot Chat Agent is running a file edit/replacement operation.

My PC specs:

• CPU: Ryzen 9 7900X
• GPU: RTX 5070 12GB
• RAM: 32GB DDR5 6000MHz
• Storage: Samsung 990 Pro NVMe SSD

The issue does not seem to be related to one specific chat session or one specific project. It appears to be related to Copilot Chat Agent / VS Code extension behavior during file replacement/evaluation, not general system performance.