litellm - 💡(How to fix) Fix [Feature]: Support Anthropic-native response format for /v1/models endpoint (Claude Code gateway discovery) [1 comments, 2 participants]

Feature Request

Summary

Claude Code 2.1.126+ added gateway model discovery: when ANTHROPIC_BASE_URL points at a compatible gateway, it queries {base_url}/v1/models at startup and populates the /model picker with discovered models labeled "From gateway".

However, this discovery only works with the Anthropic-native /v1/models response format — it does not parse the OpenAI-format response that LiteLLM currently returns.

Current Behavior

LiteLLM's /v1/models returns OpenAI format:

{
  "data": [
    {
      "id": "claude-opus-4-6",
      "object": "model",
      "created": 1677610602,
      "owned_by": "openai"
    }
  ],
  "object": "list"
}

Expected Behavior

Claude Code expects the Anthropic native format:

{
  "data": [
    {
      "type": "model",
      "id": "claude-opus-4-6",
      "display_name": "Claude Opus 4.6",
      "created_at": "2025-05-14T00:00:00Z"
    }
  ],
  "has_more": false,
  "first_id": "claude-opus-4-6",
  "last_id": "claude-haiku-4-5"
}

Key differences:

• type: "model" instead of object: "model"
• display_name field (used as label in the picker)
• created_at (ISO 8601) instead of created (unix timestamp)
• Top-level has_more, first_id, last_id instead of object: "list"

Claude Code's Discovery Filter

From the docs:

Only models whose ID begins with claude or anthropic are added to the picker. Results are cached to ~/.claude/cache/gateway-models.json.

Authentication: sends x-api-key header (or Bearer token via ANTHROPIC_AUTH_TOKEN), same as inference requests.

Proposed Solution

Since LiteLLM already supports the Anthropic /v1/messages pass-through endpoint for Claude Code users, adding an Anthropic-format response option for /v1/models would complete the compatibility story. Possible approaches:

1. Content negotiation: Return Anthropic format when the request includes anthropic-version header (same header Claude Code sends for /v1/messages)
2. Separate endpoint: Serve Anthropic-format at /anthropic/v1/models (similar to the existing /anthropic pass-through path)
3. Config option: A setting like model_list_format: anthropic to switch the /v1/models response format globally

Environment

• LiteLLM version: latest stable (deployed on EKS)
• Claude Code version: 2.1.128
• Config: Using ANTHROPIC_BASE_URL pointing to LiteLLM proxy root, with /v1/messages working correctly

Additional Context

The gateway model discovery feature was added in Claude Code 2.1.126 changelog. Many Claude Code + LiteLLM users would benefit from this since it enables seamless model switching without manual configuration.