Copilot Chat Agent: "response hit the length limit" abruptly stops with no continue option

[aNaohikoWatanabe]

Does this issue occur when all extensions are disabled?: No
Requires: GitHub Copilot Chat extension

• VS Code Version: 1.117.0
• OS Version: Windows 11 25H2 (Build 26200.0)

Steps to Reproduce:

1. Open Copilot Chat in Agent mode (Claude Opus 4.6)
2. Ask the agent to perform a large multi-file edit task (e.g., edit 20+ locations in a markdown file in a single request)
3. The agent starts editing files and generating a long response
4. Mid-response, the message is replaced with: "Sorry, the response hit the length limit. Please rephrase your prompt."

Expected: The agent should either auto-continue, offer a "Continue" button, or at least clearly indicate what was completed vs. what remains.
Actual: The response is abruptly terminated with a vague error message. Partial edits may have been applied with no summary of progress.

[amanzoori-hm]

I have the same issue in VS Code Copilot Chat Agent mode, but with Claude Sonnet 4.6 and a relatively simple task that completes without any problems when I select OpenAI models in Copilot or use the Claude Code app itself with the same model. This is quite frustrating because it is consuming a "premium request" without producing any outcome at all, and this is clearly a limitation of Github Copilot at the expense of the user.

My scenario:

• VS Code Version: 1.119.0 (user setup) - Commit: 8b640ee
• GitHub Copilot Chat Extension with Enterprise subscription
• OS: Windows 10 (Windows_NT x64 10.0.19045)
• Model: Claude Sonnet 4.6
• Mode: Agent
• Task type: MATLAB/Simulink model creation/editing

The failure happens while the agent appears to be in its internal planning/thinking stage, before it has produced a useful visible response.