@xtruder/opencode-claude-max-plugin

An OpenCode plugin that enables Claude Pro/Max subscription access via the official @anthropic-ai/sdk, using OAuth credentials from Claude Code (~/.claude/.credentials.json).

Why?

• Use your Claude subscription — Automatically reads OAuth credentials from Claude Code, no separate API key needed
• Matches Claude Code exactly — Same headers, billing, tool names, and request format as Claude Code CLI
• Prompt caching — 98% of input tokens served from cache (system prompt + tools cached globally)
• All Claude models — Opus 4.6, Sonnet 4.6, Haiku 4.5
• Extended thinking — Full reasoning support with thinking variants (high/max)
• Usage tracking — Built-in /usage command shows subscription utilization
• Self-registering — Models are registered automatically, no manual provider config needed

Installation

Add the plugin to your opencode.json (project-level or ~/.config/opencode/opencode.json globally):

{
  "$schema": "https://opencode.ai/config.json",
  "plugin": ["@xtruder/opencode-claude-max-plugin"]
}

That's it. The plugin self-registers the anthropic-sdk provider and its models (Haiku 4.5, Sonnet 4.6, Opus 4.6) at startup via the OpenCode config hook. No separate provider block is needed.

Then open OpenCode and run /connect → Other → anthropic-sdk. If Claude Code is installed and you're logged in, credentials are read automatically from ~/.claude/.credentials.json — no API key needed.

Custom model options

If you want to override model settings (e.g. thinking budgets, variants), you can add a provider block alongside the plugin:

{
  "$schema": "https://opencode.ai/config.json",
  "plugin": ["@xtruder/opencode-claude-max-plugin"],
  "provider": {
    "anthropic-sdk": {
      "models": {
        "claude-sonnet-4-6": {
          "options": {
            "thinking": { "type": "enabled", "budgetTokens": 1024 }
          },
          "variants": {
            "high": { "thinking": { "type": "enabled", "budgetTokens": 10000 } },
            "max": { "thinking": { "type": "enabled", "budgetTokens": 32000 } }
          }
        }
      }
    }
  }
}

Config-level settings are merged with plugin defaults — you only need to specify what you want to override.

Authentication

Credentials are resolved in order:

1. ANTHROPIC_API_KEY env var or apiKey provider option
2. Claude Code credentials — auto-read from ~/.claude/.credentials.json

For Claude Code credentials, log in via claude CLI first (claude auth login).

Features

• Streaming and non-streaming completions
• Tool/function calling with Claude Code tool name mapping (task → Agent, etc.)
• MCP tool name remapping (server_tool → mcp__server__tool)
• Extended thinking with signature passthrough for multi-turn conversations
• Prompt caching (98% cache hit rate with full OpenCode tool set)
• Subscription rate limit detection — fails fast with clear message instead of hanging
• Long context auto-detection — adds context-1m beta header when request body is large
• /usage slash command — shows current session and weekly utilization

Usage Command

After adding the config, run /usage inside OpenCode to see your subscription usage:

  Claude Subscription Usage
  ────────────────────────────────────────────────────
  Current session
  ████████████████████████████████░░░░░░░░░░░░░░░░░░  67% used
  Resets 7:00 PM GMT+1

  Current week (all models)
  ████░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░  8% used
  Resets Mar 30, 7:00 AM GMT+2

With Vercel AI SDK

The plugin also works as a standalone Vercel AI SDK provider:

import { createAnthropicSDK } from "@xtruder/opencode-claude-max-plugin"
import { streamText } from "ai"

// Uses ~/.claude/.credentials.json automatically
const provider = createAnthropicSDK()
const model = provider.languageModel("claude-sonnet-4-6")

const result = streamText({ model, prompt: "Hello!" })
for await (const chunk of result.textStream) {
  process.stdout.write(chunk)
}

Development

bun install
bun run build
bun run test    # integration tests (requires ANTHROPIC_API_KEY or Claude Code credentials)

See RESEARCH.md for detailed reverse-engineering findings on how we matched Claude Code's request format.

License

MIT