[FEATURE] InputValidationError in sub-agent execution when using custom ANTHROPIC_BASE_URL

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

I am encountering an issue when using Claude Agent SDK with a custom ANTHROPIC_BASE_URL and model

While the main conversation loop functions correctly, the Sub-Agent (e.g., Explore) crashes.

The root cause appears to be strict schema validation in the sub-agent's tool definition. It enforces an Enum check on the model parameter, accepting only ['sonnet', 'opus', 'haiku']. Since I am using a custom model (qwen3-max), the validation fails.

Proposed Solution

Could you please remove the strict enum validation on the model parameter for sub-agents?

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

Developer tools/SDK

Use Case Example

_No response_

Additional Context

{
    "round":4,
    "session_id":"20251223_175114",
    "message_type":"UserMessage",
    "message":{
        "parent_tool_use_id":null,
        "uuid":"da69a48d-9f57-4f1f-a0a3-0309aa4a3054",
        "content":[
            {
                "tool_use_id":"call_d32dc053b6424cec868932ca",
                "is_error":true,
                "content":"<tool_use_error>InputValidationError: [{\"received\":\"qwen3-max\",\"code\":\"invalid_enum_value\",\"options\":[\"sonnet\",\"opus\",\"haiku\"],\"path\":[\"model\"],\"message\":\"Invalid enum value. Expected 'sonnet' | 'opus' | 'haiku', received 'qwen3-max'\"}]</tool_use_error>"
            }
        ]
    },
    "timestamp":"2025-12-23T17:51:24.784456"
}

content:

[
    {
        "received": "qwen3-max",
        "code": "invalid_enum_value",
        "options": [
            "sonnet",
            "opus",
            "haiku"
        ],
        "path": [
            "model"
        ],
        "message": "Invalid enum value. Expected 'sonnet' | 'opus' | 'haiku', received 'qwen3-max'"
    }
]