Language model unavailable. Can't select models.

[Daedren]

Cannot select models in GitHub Copilot Chat Enterprise. Trying to type anything in chat yields a "Language model unavailable".
Logging out and relogging back in to chat does not fix the issue.
This used to work fine.

• Copilot Chat Extension Version: 0.47.0
• VS Code Version: 1.119.0
• OS Version: macOS 26.4.1 (25E253)
• Feature (e.g. agent/edit/ask mode): Any
• Selected model (e.g. GPT 4.1, Claude 3.7 Sonnet): can't select models. They don't show up.
• Logs:

VSCode console logs

log.ts:460   ERR Unable to resolve chat model with family selection: gpt-4o-mini: Error: Unable to resolve chat model with family selection: gpt-4o-mini
	at Mk.getChatModelFromFamily (/Applications/Visual Studio Code.app/Contents/Resources/app/extensions/copilot/dist/extension.js:6832:3354)
	at process.processTicksAndRejections (node:internal/process/task_queues:103:5)
	at async c7.getChatEndpoint (/Applications/Visual Studio Code.app/Contents/Resources/app/extensions/copilot/dist/extension.js:6832:13666)
	at async M2.provideChatTitle (/Applications/Visual Studio Code.app/Contents/Resources/app/extensions/copilot/dist/extension.js:2403:63074)
	at async dw.provideTitle (file:///Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/api/node/extensionHostProcess.js:531:26343)
	at async i.$provideChatTitle (file:///Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/api/node/extensionHostProcess.js:531:25137)

API logs for https://api.business.githubcopilot.com/models does have gpt-4o-mini

{
      "billing": {
        "is_premium": false,
        "multiplier": 0
      },
      "capabilities": {
        "family": "gpt-4o-mini",
        "limits": {
          "max_context_window_tokens": 128000,
          "max_output_tokens": 4096,
          "max_prompt_tokens": 64000
        },
        "object": "model_capabilities",
        "supports": {
          "parallel_tool_calls": true,
          "streaming": true,
          "tool_calls": true
        },
        "tokenizer": "o200k_base",
        "type": "chat"
      },
      "id": "gpt-4o-mini",
      "is_chat_default": false,
      "is_chat_fallback": false,
      "model_picker_enabled": false,
      "name": "GPT-4o mini",
      "object": "model",
      "preview": false,
      "vendor": "Azure OpenAI",
      "version": "gpt-4o-mini-2024-07-18"
    }

Output tab - "GitHub Copilot Chat"

2026-05-06 11:42:51.389 [error] TypeError: Cannot convert argument to a ByteString because the character at index 0 has a value of 65279 which is greater than 255.
	at webidl.converters.ByteString (node:internal/deps/undici/undici:4005:17)
	at Object.record<ByteString, ByteString> (node:internal/deps/undici/undici:3912:32)
	at webidl.converters.HeadersInit (node:internal/deps/undici/undici:9210:67)
	at Object.RequestInit (node:internal/deps/undici/undici:3968:21)
	at new Request (node:internal/deps/undici/undici:9767:34)
	at fetchWithSession (node:electron/js2c/utility_init:2:358)
	at n.fetch [as _fetchImpl] (node:electron/js2c/utility_init:2:17227)
	at n._fetch (/Applications/Visual Studio Code.app/Contents/Resources/app/extensions/copilot/dist/extension.js:5326:5240)
	at n.fetch (/Applications/Visual Studio Code.app/Contents/Resources/app/extensions/copilot/dist/extension.js:5326:4552)
	at $Zr (/Applications/Visual Studio Code.app/Contents/Resources/app/extensions/copilot/dist/extension.js:5326:9274)
	at iN.fetch (/Applications/Visual Studio Code.app/Contents/Resources/app/extensions/copilot/dist/extension.js:5326:13457)
	at iN.fetchWithPagination (/Applications/Visual Studio Code.app/Contents/Resources/app/extensions/copilot/dist/extension.js:5326:11742)
	at qge.makeRequest (/Applications/Visual Studio Code.app/Contents/Resources/app/extensions/copilot/dist/extension.js:1557:8204)
	at async e8.getAllSessions (/Applications/Visual Studio Code.app/Contents/Resources/app/extensions/copilot/dist/extension.js:1729:4635)
	at async Promise.all (index 0)
	at async /Applications/Visual Studio Code.app/Contents/Resources/app/extensions/copilot/dist/extension.js:2708:2962: Error in getAllSessions

[Daedren]

I'll add that fully reinstalling VSCode does not fix the problem.
I trashed the following and upon reopening VSCode and relogging into Github still leaves me with no models in chat.

~/.vscode
~/Library/Application Support/Code
~/Library/Application Support/com.apple.sharedfilelist/com.apple.LSSharedFileList.ApplicationRecentDocuments/com.microsoft.vscode.sfl*
~/Library/Caches/com.microsoft.VSCode
~/Library/Caches/com.microsoft.VSCode.ShipIt
~/Library/HTTPStorages/com.microsoft.VSCode
~/Library/Preferences/ByHost/com.microsoft.VSCode.ShipIt.*.plist
~/Library/Preferences/com.microsoft.VSCode.helper.plist
~/Library/Preferences/com.microsoft.VSCode.plist
~/Library/Saved Application State/com.microsoft.VSCode.savedState