Claude Code Custom Model Proxy

This skill helps configure Claude Code to work with custom model providers that use OpenAI API format (like MiniMax) by setting up a proxy server that converts between Anthropic Messages API and OpenAI Chat Completions API.

When to Use This Skill

• User wants to use Claude Code with a custom model provider (not Anthropic)
• User's model provider uses OpenAI Chat Completions API format
• User sees errors like "There's an issue with the selected model" in Claude Code
• User needs to convert between Anthropic API format and OpenAI API format

Overview

Claude Code uses Anthropic Messages API format (/v1/messages), but many custom model providers (like MiniMax) use OpenAI Chat Completions API format (/v1/chat/completions). This skill provides a Python proxy server that:

1. Listens on http://127.0.0.1:4002
2. Accepts Anthropic API format requests from Claude Code
3. Converts to OpenAI API format
4. Forwards to the upstream provider
5. Converts responses back to Anthropic SSE format
6. Handles model validation, URL query strings, and UTF-8 encoding

Quick Start

1. Configure Claude Code

Create or edit ~/.claude/settings.json:

{
  "env": {
    "ANTHROPIC_BASE_URL": "http://127.0.0.1:4002",
    "ANTHROPIC_API_KEY": "fake-key-not-needed"
  }
}

Or use environment variables:

export ANTHROPIC_BASE_URL="http://127.0.0.1:4002"
export ANTHROPIC_API_KEY="fake-key"

2. Start the Proxy Server

python3 ~/.workbuddy/skills/claude-code-custom-model-proxy/scripts/claude_code_proxy.py

Or run in background:

nohup python3 ~/.workbuddy/skills/claude-code-custom-model-proxy/scripts/claude_code_proxy.py > /tmp/claude_proxy.log 2>&1 &

3. Start Claude Code

claude --model sonnet

Proxy Server Configuration

Edit scripts/claude_code_proxy.py to configure:

• UPSTREAM_HOST: Your provider's API host (e.g., "api.53hk.cn")
• UPSTREAM_PATH: API path (e.g., "/v1/chat/completions")
• API_KEY: Your provider's API key
• LISTEN_PORT: Proxy listen port (default: 4002)
• Forced model name (line 44): Change "MiniMax-M2.7-highspeed" to your model

Common Issues and Solutions

Issue 1: "There's an issue with the selected model"

Cause: Claude Code validates model names locally before connecting to the API.

Solution: The proxy's GET /v1/models endpoint must return the model name Claude Code expects.

For --model sonnet, Claude Code expects claude-sonnet-4-6 in the models list.

The proxy already includes common model names in its response. Add more if needed:

models = {
    "data": [
        {"type": "model", "id": "claude-sonnet-4-6", "display_name": "Claude Sonnet 4.6"},
        {"type": "model", "id": "claude-opus-4-5", "display_name": "Claude Opus 4.5"},
        # Add more models as needed
    ]
}

Issue 2: 404 errors in proxy logs

Cause: Claude Code sends requests with query strings (e.g., POST /v1/messages?beta=true), but the proxy only checks self.path == "/v1/messages".

Solution: The proxy now uses urlparse() to extract the path without query string:

from urllib.parse import urlparse

parsed_path = urlparse(self.path)
path = parsed_path.path  # This removes ?beta=true

Issue 3: Chinese characters appear as garbled text (乱码)

Cause: Incorrect handling of UTF-8 encoding in SSE streaming.

Solution: Use byte buffer instead of string buffer:

buffer = b""  # Byte buffer
for chunk in r.iter_content(chunk_size=None, decode_unicode=False):
    if chunk:
        buffer += chunk
        while b"\
" in buffer:
            line_bytes, buffer = buffer.split(b"\
", 1)
            line = line_bytes.strip().decode("utf-8", errors="replace")

Issue 4: Connection refused

Cause: Proxy server is not running.

Solution: Start the proxy server before starting Claude Code. Check with:

lsof -i :4002

API Format Conversion

Anthropic Messages API (Claude Code) → OpenAI Chat Completions (Provider)

Request conversion (anthropic_to_openai()):

• messages array: Extract text from content blocks
• max_tokens → max_tokens
• temperature → temperature
• stream: true (always enabled)

Response conversion (openai_to_anthropic()):

• OpenAI SSE chunks → Anthropic SSE events:
  • message_start
  • content_block_start
  • content_block_delta
  • content_block_stop
  • message_delta
  • message_stop

Troubleshooting

Check proxy logs

tail -f /tmp/claude_proxy.log

Test proxy endpoints

# Test models endpoint
curl -s http://127.0.0.1:4002/v1/models | python3 -m json.tool

# Test messages endpoint
curl -X POST http://127.0.0.1:4002/v1/messages \
  -H "Content-Type: application/json" \
  -d '{"model":"claude-sonnet-4-6","messages":[{"role":"user","content":"Hello"}],"max_tokens":100}'

Check Claude Code debug logs

ls -lt ~/.claude/debug/*.txt | head -1
tail -50 ~/.claude/debug/\x3Clatest>.txt

File Structure

~/.workbuddy/skills/claude-code-custom-model-proxy/
├── SKILL.md                    # This file
└── scripts/
    └── claude_code_proxy.py    # Proxy server

Advanced Configuration

Change forced model

In claude_code_proxy.py, line 44:

"model": "MiniMax-M2.7-highspeed",  # Change this to your model

Change listen port

In claude_code_proxy.py:

LISTEN_PORT = 4002  # Change to your preferred port

Then update ANTHROPIC_BASE_URL accordingly.

Add retry logic for 429 errors

The proxy already includes retry logic (call_upstream_with_retry()). Configure:

• MAX_RETRIES: Maximum retry attempts (default: 3)
• BASE_WAIT_SECONDS: Base wait time between retries (default: 10)