Task Tool Model Parameter Causes API 404 Error

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Version: Claude Code 2.0.42
Platform: Linux (WSL2)
Date: 2025-11-15

Issue Description

When using the Task tool with the optional model parameter set to "sonnet", "opus", or "haiku", the API returns a 404 error because the short model name is not being resolved to the full model ID before making the API call.

Steps to Reproduce

1. Launch Claude Code (version 2.0.42)
2. Use the Task tool with a model parameter:

{
  "description": "Find personality type algorithm",
  "prompt": "Explore this Django project...",
  "subagent_type": "Explore",
  "model": "sonnet"
}

1. Receive the following error:

API Error: 404 {"type":"error","error":{"type":"not_found_error","message":"model: sonnet"},"request_id":"req_011CV9MB7Uz8wyruj5Xmbj4s"}

Expected Behavior

The model parameter "sonnet" should be resolved to the full model ID (e.g., "claude-sonnet-4-5-20250929") before making the API call, as defined in the Task tool schema:

"model": {
  "description": "Optional model to use for this agent...",
  "enum": ["sonnet", "opus", "haiku"],
  "type": "string"
}

What Should Happen?

Actual Behavior

The API receives "sonnet" as the literal model name instead of the full model ID, resulting in a 404 not found error.

Workaround

Avoid specifying the model parameter in Task tool calls. The subagent will inherit the parent's model, which works correctly.

Environment Details

• Node.js: v24.7.0
• Claude Code: 2.0.42 (installed via npm globally)
• OS: Linux 6.6.87.2-microsoft-standard-WSL2
• Authentication: OAuth (Claude Max)

Additional Context

The cli.js file contains references to full model IDs like "claude-sonnet-4-5", "claude-opus", "claude-haiku" for Vertex region configuration, but the model alias resolution for Task tool subagents appears to be missing or broken.

Error Messages/Logs

API Error: 404 {"type":"error","error":{"type":"not_found_error","message":"model: sonnet"},"request_id":"req_011CV9MB7Uz8wyruj5Xmbj4s"}

Steps to Reproduce

1. Launch Claude Code (version 2.0.42)
2. Use the Task tool with a model parameter:

{
  "description": "Find personality type algorithm",
  "prompt": "Explore this Django project...",
  "subagent_type": "Explore",
  "model": "sonnet"
}

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.0.42

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_