max_tokens not being set for Opus 4.7 and Opus 4.8 models when using Azure Foundry with Github Copilot

[ot513]

When adding models deployed to Azure Foundry to be used as the model for Github Copilot coding, I get this error when using Opus 4.7 or 4.8 models:

2026-06-09 14:25:29.414 [error] Unable to call the (redacted)claude-opus-4-8 inference endpoint due to 400. Please check if the input or configuration is correct. 400 {"type":"error","error":{"type":"invalid_request_error","message":"max_tokens: Field required"},"request_id":"req_011Cbsm6PDRYKidbivY8T2vP"}

Github Copilot for Azure extension:
Identifier
ms-azuretools.vscode-azure-github-copilot
Version
1.0.209

Foundry Toolkit for VS Code extension:
Identifier
ms-windows-ai-studio.windows-ai-studio
Version
1.4.2

VS Code:
Version: 1.123.0 (user setup)
Commit: 6a44c352bd24569c417e530095901b649960f9f8
Date: 2026-06-03T11:29:03+02:00
Electron: 42.2.0
ElectronBuildId: 14159160
Chromium: 148.0.7778.97
Node.js: 24.15.0
V8: 14.8.178.14-electron.0
OS: Windows_NT x64 10.0.26200

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[vritant24]

I think this is due to how the model provider the foundry extension makes the chat request as pointed out in this comment.
microsoft/vscode#313527 (comment)

[ot513]

Same issue occurring with Claude Fable 5 model.

[ot513]

Before you try and suggest I haven't got the latest version, I have updated and retested and the same issue occurs:

Version: 1.123.2 (user setup)
Commit: 3c631b164c239e7aeaaae7c626b46c527b361af2
Date: 2026-06-09T15:06:40-07:00
Electron: 42.2.0
ElectronBuildId: 14159160
Chromium: 148.0.7778.97
Node.js: 24.15.0
V8: 14.8.178.14-electron.0
OS: Windows_NT x64 10.0.26200

Foundry Toolkit for VS Code
Identifier
ms-windows-ai-studio.windows-ai-studio
Version
1.4.3

GitHub Copilot for Azure
Identifier
ms-azuretools.vscode-azure-github-copilot
Version
1.0.209