[Claude] Can only use github mcp server with Haiku model

[rafa-moraes-fortis]

Describe the bug

Claude is unable to run the MCP server request if using any other model than Haiku
It always returns this error
⎿  API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools.21.custom.defer_loading: Extra inputs are not permitted"},"request_id":"requestid"}

{
  "mcpServers": {
    "github": {
      "type": "http",
      "url": "https://api.githubcopilot.com/mcp",
      "headers": {
        "Authorization": "Bearer ${GITHUB_PAT}"
      }
    }
  }
}

Affected version

Using API Server

Steps to reproduce the behavior

1. Use the same .mcp.json config
2. Set up the GITHUB PAT in your env
3. Try to run any mcp command, something like "get my GitHub user with mcp" or mcp__github__get_me

Expected vs actual behavior

The MCP command should run without any issues

Logs

Paste any available logs. Redact if needed.

[SamMorrowDrums]

@rafa-moraes-fortis before I escalate, can you confirm for me that your version of Claude is fully up-to-date?

[SamMorrowDrums]

FWIW this bug is coming from the Anthropic Tool Search Tool model API, and that would explain why Haiku is not showing the same issue. Presumably that model doesn't support Tool Search Tool.

[rafa-moraes-fortis]

@SamMorrowDrums I'm using the latest 2.1.39
Got it, thanks for the info

[rafa-moraes-fortis]

To add new info, this error only started happening after I added the GitHub MCP to my settings earlier. Initially, I only had the ClickUp MCP set up. After adding the GitHub MCP, all the MCPs failed

[almaleksia]

As said earlier defer_loading is a custom tool parameter for Claude search API. We do not return it as part of tool metadata. The fact that adding GitHub MCP can result in Claude Code adding defer_loading to tools might be explained by Claude Code deciding to use tool search after number of tools crosses some threshold. In this case adding any other MCP server with the same amount of tools would result in this error. So this bug report is for Claude Code team, closing it.