@elizaos/plugin-anthropic-proxy

Routes Anthropic API traffic from your eliza agent through a Claude Max / Pro subscription instead of paying per-token Extra Usage rates.

This plugin is a port of the standalone Anthropic routing layer that has been running in production for ~6 weeks. The 7-layer transformation algorithm is byte-identical to the original proxy.js v2.2.3. The fingerprint dictionaries, however, are framework-specific:

• v0.2.0+ ships eliza-default dictionaries derived by profiling @elizaos/native-reasoning's outbound /v1/messages calls. They map eliza tool names (bash, read_file, spawn_agent, ...) onto Claude-Code-shaped names (Bash, Read, Agent, ...) and strip eliza-distinctive system-prompt blocks (the CHANNEL_GAG_HARD_RULE).
• For non-eliza agents, supply your own dictionaries via config.json (see config.json.example).

Why this exists

In April 2026 Anthropic upgraded their detection beyond simple string matching to tool-name fingerprinting and system-prompt-template detection. v1.x string-only sanitization stopped working. The proxy this plugin embeds applies seven transformation layers (bidirectional) so requests look like they originate from the official Claude Code CLI:

1. Billing header injection (84-char Claude Code identifier with dynamic SHA256 fingerprint per request)
2. String trigger sanitization
3. Tool name fingerprint bypass (PascalCase CC convention rename)
4. System prompt template bypass (strip + paraphrase)
5. Tool description stripping (reduce schema fingerprint)
6. Schema property name renaming
7. Full bidirectional reverse mapping on SSE + JSON responses

Plus assistant-prefill stripping and thinking-block stripping for replay/session bugs.

Custom fingerprint dictionaries

The defaults make this plugin a one-line drop-in for any eliza agent. If you're running a non-eliza agent (LangChain, LlamaIndex, your own runtime, etc.) the eliza tool-name dictionary won't match your tool surface and you'll want to supply your own.

Drop a config.json next to your eliza root with the shape shown in config.json.example. The plugin merges it over the defaults at startup. Any of the four dictionaries (replacements, toolRenames, propRenames, reverseMap) can be overridden independently — the rest fall back to the eliza defaults.

You own the subscription

This plugin does not route your traffic through any service operated by anyone but you. It needs your Claude Code OAuth token (from your own subscription on your own machine). You are responsible for whether your usage complies with Anthropic's terms.

Setup

# 1. Install Claude Code CLI and log in once on this machine.
claude auth login

# 2. Add the plugin to your agent's plugin list (your character file or
#    plugin loader). It will:
#    - Start an in-process proxy on http://127.0.0.1:18801
#    - Set ANTHROPIC_BASE_URL to that proxy URL (unless you've set it
#      explicitly to something else)

Modes

Pick via CLAUDE_MAX_PROXY_MODE:

In inline mode each agent gets its own proxy server. In shared mode you run the proxy once on the host (or via this same plugin in a different agent) and point all your agents at the same CLAUDE_MAX_PROXY_UPSTREAM. Useful when you have many agents on one box and only one Claude subscription.

Environment variables

Diagnostics

• HTTP route: GET /api/anthropic-proxy/status returns the current mode, URL, listening state, request count, token expiry, and (in shared mode) upstream reachability.
• Action: PROXY_STATUS returns the same info to a chat surface.
• Local proxy health: GET http://127.0.0.1:18801/health (replace port to match config).

Token refresh

If you hit a 401 (token expired) run:

claude auth login

The plugin re-reads the credentials file on every request, so a fresh login is picked up immediately — no need to restart the agent. Auto-rotation isn't included in this v0.1.0 release.

Failure modes (intentional)

• Missing credentials. Plugin logs a warning, degrades to off mode, agent keeps running. It does not crash.
• Inline port collision. Plugin logs the bind error, degrades to off mode.
• Shared upstream unreachable at startup. Plugin still boots in shared mode; the unreachable upstream is reported via /api/anthropic-proxy/status.

Plugin shape

• services: [AnthropicProxyService] — Service that owns the http server lifecycle (start/stop)
• actions: [proxyStatusAction] — PROXY_STATUS action for in-chat diagnostics
• routes: anthropicProxyRoutes — GET /api/anthropic-proxy/status for external tools
• init() — sets ANTHROPIC_BASE_URL if you haven't already

Files

plugins/plugin-anthropic-proxy/
├── index.ts                           # Plugin export + init
├── index.node.ts                      # Node entry
├── index.browser.ts                   # Browser noop
├── build.ts                           # Bun build script
├── package.json
├── tsconfig.json / tsconfig.build.json
├── vitest.config.ts
├── bunfig.toml
├── src/
│   ├── proxy/
│   │   ├── constants.ts               # Bit-for-bit constants from proxy.js
│   │   ├── billing-fingerprint.ts     # Layer 1: SHA256 fingerprint
│   │   ├── sanitize.ts                # Layer 2: string sanitize
│   │   ├── tool-rename.ts             # Layer 3/6: quoted name renames
│   │   ├── system-prompt.ts           # Layer 4: system strip + paraphrase
│   │   ├── cc-tool-stubs.ts           # Layer 5: description strip + stubs
│   │   ├── sse-rewrite.ts             # Tail-buffer SSE reverse map
│   │   ├── stainless-headers.ts       # CC-emulating SDK headers
│   │   ├── process-body.ts            # Forward request pipeline
│   │   ├── reverse-map.ts             # Response/SSE reverse pipeline
│   │   └── server.ts                  # http.createServer lifecycle
│   ├── services/
│   │   └── proxy-service.ts           # AnthropicProxyService extends Service
│   ├── actions/
│   │   └── proxy-status.action.ts     # PROXY_STATUS action
│   ├── routes/
│   │   └── status-route.ts            # /api/anthropic-proxy/status
│   └── utils/
│       └── credentials-loader.ts      # ~/.claude/.credentials.json + JWT exp
└── __tests__/
    └── proxy.test.ts                  # vitest suite

Version

0.1.0 — initial port from ocplatform-routing-layer/proxy.js v2.2.3.

Algorithm changes happen upstream first. This package follows.