@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 — Sidebar widget with live progress bars + /usage command with full details
• 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.

In OpenCode, the plugin also replaces the default base system prompt with a Claude-compatible one via experimental.chat.system.transform. This is required for Claude Code OAuth requests to be treated as Claude-native rather than third-party app requests.

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.

TUI Plugin (sidebar + /usage command)

The plugin includes a TUI component that shows subscription usage in the sidebar and registers a /usage slash command. To enable it, add the plugin to your tui.json as well:

Project-level (.opencode/tui.json):

{
  "plugin": ["@xtruder/opencode-claude-max-plugin"]
}

Or globally (~/.config/opencode/tui.json):

{
  "plugin": ["@xtruder/opencode-claude-max-plugin"]
}

The TUI plugin provides:

• Sidebar widget — Compact progress bars for 5-hour session and 7-day weekly usage
• /usage command — Opens a dialog with full usage breakdown (per-model, extra usage)
• Auto-refresh — Polls the usage API every 60s and after each inference call

TUI Configuration

Options can be set in the tui.json plugin entry:

{
  "plugin": [
    [
      "@xtruder/opencode-claude-max-plugin",
      {
        "enabled": true,
        "sidebar": true,
        "poll_interval": 60
      }
    ]
  ]
}

| Option | Type | Default | Description | | --------------- | ------- | ------- | ----------------------------------------- | | enabled | boolean | true | Enable/disable the TUI plugin entirely | | sidebar | boolean | true | Show/hide sidebar usage widget | | poll_interval | number | 60 | Seconds between usage API polls (min: 10) |

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)
• CCH request signing — computes xxHash64 body integrity hash to unlock features like fast mode
• 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
• TUI sidebar with live usage bars + /usage slash command with full subscription details

With Vercel AI SDK

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

import { CLAUDE_CODE_SYSTEM_PROMPT, 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,
  system: CLAUDE_CODE_SYSTEM_PROMPT,
  prompt: "Hello!",
})
for await (const chunk of result.textStream) {
  process.stdout.write(chunk)
}

When using Claude Code OAuth credentials outside OpenCode, you must pass a Claude-compatible system prompt yourself. Exported CLAUDE_CODE_SYSTEM_PROMPT is the prompt used by the OpenCode plugin hook.

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