Fix for model not supported error in GitHub Copilot

github-copilot-model-not-supported-error-fix.md

Manual Fix for GitHub Copilot Chat "Model Not Supported" Error

This guide shows how to manually apply the fix to remove the x-onbehalf-extension-id header from the GitHub Copilot Chat extension.

Manual Fix Steps

1. Locate the GitHub Copilot Chat Extension

Windows:

cd $env:USERPROFILE\.vscode\extensions
dir github.copilot-chat-*

macOS/Linux:

cd ~/.vscode/extensions
ls -la | grep github.copilot-chat

2. Navigate to the dist Folder

# Replace <version> with the actual version number found in step 1
cd github.copilot-chat-<version>\dist

3. Create a Backup (Important!)

Windows:

copy extension.js extension.js.backup-manual

macOS/Linux:

cp extension.js extension.js.backup-manual

4. Edit the File

Open extension.js in any text editor:

Using VS Code:

code extension.js

Or use any text editor:

• Notepad (Windows)
• TextEdit (macOS)
• vim/nano (Linux)

5. Find and Remove the Header

The file is minified (all on one line), so use Find & Replace:

Search for:

,"x-onbehalf-extension-id":

You'll find something like:

S==="getExtraHeaders"?function(){return{...f.getExtraHeaders?.()??{},"x-onbehalf-extension-id":`${A}/${c}`}}:

Remove this part:

,"x-onbehalf-extension-id":`${A}/${c}`

So it becomes:

S==="getExtraHeaders"?function(){return{...f.getExtraHeaders?.()??{}}}:

6. Save the File

• VS Code: Ctrl+S (Windows/Linux) or Cmd+S (macOS)
• Other editors: Use File → Save

7. Reload VS Code

1. Open Command Palette: Ctrl+Shift+P (Windows/Linux) or Cmd+Shift+P (macOS)
2. Type and select: Developer: Reload Window

8. Verify the Fix

After reload, search for x-onbehalf-extension-id in the file again - it should not be found.

Quick PowerShell Script (Windows)

For advanced users, here's a one-liner script to apply the fix automatically:

# Find the extension
$extPath = Get-ChildItem "$env:USERPROFILE\.vscode\extensions" -Filter "github.copilot-chat-*" | Select-Object -First 1
$jsFile = Join-Path $extPath.FullName "dist\extension.js"

# Create timestamped backup
Copy-Item $jsFile "$jsFile.backup-$(Get-Date -Format 'yyyy-MM-ddTHH-mm-ss')"

# Read, modify, and write
$content = Get-Content $jsFile -Raw
$content = $content -replace ',"x-onbehalf-extension-id":`\$\{[^}]+\}/\$\{[^}]+\}`', ''
Set-Content $jsFile $content -NoNewline

Write-Host "Fix applied! Please reload VS Code." -ForegroundColor Green

To run:

1. Copy the script above
2. Open PowerShell
3. Paste and press Enter
4. Reload VS Code when prompted

Quick Bash Script (macOS/Linux)

#!/bin/bash

# Find the extension
EXT_DIR=$(find ~/.vscode/extensions -maxdepth 1 -name "github.copilot-chat-*" | head -n 1)
JS_FILE="$EXT_DIR/dist/extension.js"

# Create timestamped backup
BACKUP_FILE="$JS_FILE.backup-$(date +%Y-%m-%dT%H-%M-%S)"
cp "$JS_FILE" "$BACKUP_FILE"

# Apply the fix
sed -i.tmp 's/,"x-onbehalf-extension-id":`\${[^}]*}\/\${[^}]*}`//g' "$JS_FILE"
rm "$JS_FILE.tmp"

echo "Fix applied! Backup saved to: $BACKUP_FILE"
echo "Please reload VS Code."

To run:

1. Save the script to a file (e.g., fix-copilot.sh)
2. Make it executable: chmod +x fix-copilot.sh
3. Run it: ./fix-copilot.sh
4. Reload VS Code

Restore from Backup

If something goes wrong or you want to undo the fix:

Windows:

copy extension.js.backup-manual extension.js

macOS/Linux:

cp extension.js.backup-manual extension.js

Then reload VS Code.

Troubleshooting

Can't Find the Extension

Make sure GitHub Copilot Chat is installed:

1. Open VS Code Extensions (Ctrl+Shift+X)
2. Search for "GitHub Copilot Chat"
3. Install if not already installed

Permission Denied

Windows:

• Run PowerShell as Administrator
• Or close VS Code before editing

macOS/Linux:

• Use sudo if necessary
• Or close VS Code before editing

Pattern Not Found

The extension might:

• Already be fixed
• Use a different version/format
• Be corrupted (try reinstalling)

Fix Gets Overwritten

After GitHub Copilot Chat updates, you'll need to reapply the fix.

Notes

⚠️ Important Warnings:

• The extension.js file is minified (all on one line), so it's hard to read manually
• Always create a backup before editing
• You'll need to reapply this fix after GitHub Copilot Chat updates