Bypassing Anthropic block in OpenClaw: guide

Bypassing Anthropic's Server-Side Block on Third-Party Clients: Technical Breakdown

Anthropic has rolled out server-side checks on API request sources. Requests from official Claude Code and Cowork clients are covered by Pro subscriptions. Third-party tools like OpenClaw get routed to Extra Usage mode with per-token API billing, jacking up costs significantly. Simple HTTP requests with spoofed headers don't cut it—the server digs into the request body.

Goal: Make requests indistinguishable from official clients while keeping OpenClaw's 17-tool functionality intact.

Request Structure Analysis

Anthropic API requests are JSON payloads with system prompts, message history, metadata, and a tools list. Testing revealed:

• System prompts and history pass muster.
• Adding tools triggers detection.

Breaking down tools by group pinpointed the culprits:

• read, edit, write — pass.
• exec, process — pass.
• sessions_list, sessions_history, sessions_send — pass.
• web_search, web_fetch — pass.
• image, memory_search, memory_get — pass.
• subagents — blocked.
• session_status — blocked.

Anthropic's server scans for tool names absent from Claude Code. Just two of the 17 tools are enough to trigger Extra Usage.

Proxy Chain Architecture

Solution: A two-tier proxy setup between OpenClaw and api.anthropic.com.

• CLIProxyAPI (Go, 23k GitHub stars): Mimics Claude Code headers (user-agent, billing header, client_id). OAuth auth—proxy generates a URL, you log in via browser, and refresh_token is stored locally.

• Replace-proxy (Node.js, 133 lines, no dependencies): Intercepts JSON in both directions.

- Outbound: subagents → sub_dispatch, session_status → check_status, OpenClaw → Assistant.

- Inbound: Reverse swaps line-by-line for streaming.

Chain: OpenClaw (port 8318) → replace-proxy → CLIProxyAPI (8317) → api.anthropic.com.

Replace-proxy runs as a systemd service with auto-restart.

Setting Up Replace-Proxy

The proxy code is lean: HTTP server parses bodies, applies regex swaps, and buffers streaming events.

// Sample snippet: Handling outbound requests
const replaceMap = {
  'subagents': 'sub_dispatch',
  'session_status': 'check_status',
  'OpenClaw': 'Assistant'
};
// JSON.parse(body).tools.forEach(tool => {
//   if (replaceMap[tool.name]) tool.name = replaceMap[tool.name];
// });
// Similar for responses

Server listens on localhost:8318, forwards to CLIProxyAPI:8317.

Configuring OpenClaw

Add a provider in openclaw.json:

{
  "models": {
    "providers": {
      "custom-proxy": {
        "baseUrl": "http://localhost:8318",
        "apiKey": "<api-key-from-CLIProxyAPI>",
        "api": "anthropic-messages",
        "models": [
          {"id": "claude-opus-4-6", "contextWindow": 1000000, "maxTokens": 16384},
          {"id": "claude-sonnet-4-6", "contextWindow": 200000, "maxTokens": 16384}
        ]
      }
    }
  }
}

Set as default:

openclaw config set "agents.defaults.model.primary" "custom-proxy/claude-opus-4-6"

Restart OpenClaw. Model switching works in-chat.

Key Takeaways

• Tool-Based Detection: Anthropic inspects tool names in the JSON body. OpenClaw uniques (subagents, session_status) trigger Extra Usage.
• Two-Tier Proxy: CLIProxyAPI hides headers, replace-proxy scrubs content.
• OAuth Auth: CLIProxyAPI auto-refreshes tokens; re-auth on refresh_token expiry.
• Streaming Support: Replace-proxy buffers events for real-time swaps.
• Risks: Bypasses Anthropic ToS. Account bans possible; detection could evolve (prompt patterns, structure).

Limitations and Monitoring

• Not for production: Personal use at your own risk.
• Monitoring: Check proxy logs for swap errors or new detections.
• Scaling: Systemd keeps it stable, but Anthropic updates may need replace-map tweaks.

Testing confirmed it works on Opus 4.6 and Sonnet 4.6 without Extra Usage.

— Editorial Team