Copilot CLI (handsoff) from VS Code fails with "model_not_supported" error since 1.119

[fighterii]

Type: Bug

VS Code Version: 1.119.0-insider (system setup)
Commit: 530cb5d
Date: 2026-05-03T14:51:49-07:00
Electron: 39.8.8
ElectronBuildId: 13870025
Chromium: 142.0.7444.265
Node.js: 22.22.1
V8: 14.2.231.22-electron.0
OS: Windows_NT x64 10.0.22631

Description

Since updating to VS Code Insiders 1.119, the Copilot CLI agent mode (handsoff, launched from within VS Code) fails with a 400 model_not_supported error. The issue occurs with all models (not just Claude). The request retries twice and then gives up.

This worked in 1.118 and still works in these scenarios:

• Copilot CLI running as a standalone terminal session (outside VS Code)
• VS Code local chat sessions (non-CLI)

Downgrading to 1.118 resolves the issue immediately.

Suspected cause

The GitHub Copilot model access is provided through a GitHub Enterprise (GHE) instance. The new 1.119 build may be sending the model identifier differently to the API backend when routing through GHE, or the CopilotCLI session may no longer correctly negotiate available models with the GHE-proxied endpoint.

Steps to Reproduce

1. Use VS Code Insiders 1.119 with Copilot connected via a GitHub Enterprise instance
2. Launch a Copilot CLI handsoff session from within VS Code
3. Send any query
4. Observe model_not_supported error regardless of selected model

Expected behavior

The request should succeed and produce a response, as it does in 1.118 and in standalone Copilot CLI.

Actual behavior

The request fails immediately with:

{
  "message": "The requested model is not supported.",
  "code": "model_not_supported",
  "param": "model",
  "type": "invalid_request_error"
}

HTTP status: 400
Retries: 2/2 (all fail identically)
Affects: All models (tested with claude-sonnet-4.6 and others)

Logs (trace level)

[CopilotCLI] Failed to get response from the AI model: CAPIError: 400 The requested model is not supported.
[CopilotCLI] Inner error: {
  "message": "The requested model is not supported.",
  "code": "model_not_supported",
  "param": "model",
  "type": "invalid_request_error"
}

Full stack trace:

CAPIError: 400 The requested model is not supported.
    at t.fromAPIError (file:///c:/Program%20Files/Microsoft%20VS%20Code%20Insiders/530cb5de71/resources/app/extensions/copilot/node_modules/@github/copilot/sdk/index.js:1162:1046)
    at P4e.getCompletionWithTools (…/sdk/index.js:2045:13327)
    at async AIe.getCompletionWithTools (…/sdk/index.js:2063:3520)
    at async t.runAgenticLoop (…/sdk/index.js:3900:3914)
    at async t.processQueuedItems (…/sdk/index.js:3898:10220)
    at async Q4.sendRequestInternal (…/dist/extension.js:2393:2509)
    at async Q4._handleRequestImplInner (…/dist/extension.js:2391:1592)

Additional context

• Token utilization at time of failure: 20% (33551/168000) — not a token limit issue
• The session.usage_info event shows normal values (systemTokens: 14628, conversationTokens: 164, toolDefinitionsTokens: 18755)
• Provider call IDs for server-side correlation: BEF5:203DEE:38222F:F0814E:69F86018, BEF5:203DEE:3823A4:F08A69:69F86019, BEF5:203DEE:3824F3:F093EF:69F8601A
• Works fine with the exact same GHE setup on 1.118
• Standalone copilot CLI outside VS Code works fine with the same account

[fighterii]

Additional information: As mentioned in #304075 (comment) i provided the workaround to get Copilot CLI working with GHE by setting env variable:
COPILOT_API_URL=https://copilot-api.<tenant>.ghe.com
Might be a related issue.

[rennanfelizardo]

Same happens for GHE instances, this only happens when delegating session to copilot CLI.
I've gh auth authenticated to the ghe instance, copilot cli is also authenticated, and even have the github-enterprise.uri setting defined.
GH_HOST and COPILOT_API_URL variables are also pointing to the ghe instance.

Version: 1.120.0-insider (Universal)
Commit: 79d6cea
Date: 2026-05-05T12:39:31+02:00
Electron: 39.8.8
ElectronBuildId: 13870025
Chromium: 142.0.7444.265
Node.js: 22.22.1
V8: 14.2.231.22-electron.0
OS: Darwin arm64 25.4.0

Error Details
Type: query Message: Execution failed: CAPIError: 400 The requested model is not supported. (Request ID: D7DE:120D01:E26A:2543A:69F9E31E)

{
  "status": 400,
  "headers": {},
  "requestID": "643fbaed-f286-9861-bc12-61a4dd8e1c59",
  "error": {
    "message": "The requested model is not supported.",
    "code": "model_not_supported",
    "param": "model",
    "type": "invalid_request_error"
  },
  "code": "model_not_supported",
  "param": "model",
  "type": "invalid_request_error",
  "request_id": "643fbaed-f286-9861-bc12-61a4dd8e1c59",
  "ghRequestId": "D7DE:120D01:E26A:2543A:69F9E31E",
  "name": "CAPIError",
  "message": "400 The requested model is not supported.",
  "stack": "CAPIError: 400 The requested model is not supported.\n\tat t.fromAPIError (file:///Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/extensions/copilot/node_modules/@github/copilot/sdk/index.js:1162:1046)\n\tat P4e.getCompletionWithTools (file:///Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/extensions/copilot/node_modules/@github/copilot/sdk/index.js:2045:13327)\n\tat process.processTicksAndRejections (node:internal/process/task_queues:103:5)\n\tat async AIe.getCompletionWithTools (file:///Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/extensions/copilot/node_modules/@github/copilot/sdk/index.js:2063:3520)\n\tat async t.runAgenticLoop (file:///Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/extensions/copilot/node_modules/@github/copilot/sdk/index.js:3900:3914)\n\tat async t.processQueuedItems (file:///Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/extensions/copilot/node_modules/@github/copilot/sdk/index.js:3898:10220)\n\tat async t.processQueue (file:///Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/extensions/copilot/node_modules/@github/copilot/sdk/index.js:3898:3024)\n\tat async t.send (file:///Applications/Visual%20Studio%20Code%20-%20Insiders.app/Contents/Resources/app/extensions/copilot/node_modules/@github/copilot/sdk/index.js:3896:3966)\n\tat async F4.sendRequestInternal (/Applications/Visual Studio Code - Insiders.app/Contents/Resources/app/extensions/copilot/dist/extension.js:2496:2509)\n\tat async F4._handleRequestImplInner (/Applications/Visual Studio Code - Insiders.app/Contents/Resources/app/extensions/copilot/dist/extension.js:2494:1282)\n\tat async /Applications/Visual Studio Code - Insiders.app/Contents/Resources/app/extensions/copilot/dist/extension.js:2491:1098\n\tat async /Applications/Visual Studio Code - Insiders.app/Contents/Resources/app/extensions/copilot/dist/extension.js:6273:2555"
}

[fighterii]

Will be fixed by #314724