opencode-anthropic-context-1m

OpenCode plugin that enables the 1M token context window for supported Anthropic Claude models.

Without this plugin, the API enforces a 200K input token limit. This plugin injects the context-1m-2025-08-07 beta flag, unlocking the full 1M context.

Supports both Anthropic direct API and Amazon Bedrock.

Supported Models

• Claude Opus 4.6
• Claude Sonnet 4.6
• Claude Sonnet 4.5
• Claude Sonnet 4

Requirements

• Anthropic direct: API key with Usage Tier 4 ($400+ cumulative deposit) or custom rate limits
• Amazon Bedrock: Bedrock access with Claude model enabled in your region
• Requests exceeding 200K input tokens are billed at long-context rates (2x input, 1.5x output)

Installation

Anthropic Direct API

Add to your opencode.json:

{
  "plugin": ["opencode-anthropic-context-1m"],
  "provider": {
    "anthropic": {
      "models": {
        "claude-opus-4-6":          { "limit": { "context": 1000000, "output": 128000 } },
        "claude-sonnet-4-6":        { "limit": { "context": 1000000, "output": 64000 } },
        "claude-sonnet-4-5":        { "limit": { "context": 1000000, "output": 64000 } },
        "claude-sonnet-4-20250514": { "limit": { "context": 1000000, "output": 64000 } }
      }
    }
  }
}

Amazon Bedrock

{
  "plugin": ["opencode-anthropic-context-1m"],
  "provider": {
    "amazon-bedrock": {
      "models": {
        "anthropic.claude-opus-4-6-v1":              { "limit": { "context": 1000000, "output": 128000 } },
        "anthropic.claude-sonnet-4-6":               { "limit": { "context": 1000000, "output": 64000 } },
        "anthropic.claude-sonnet-4-5-20250929-v1:0": { "limit": { "context": 1000000, "output": 64000 } },
        "anthropic.claude-sonnet-4-20250514-v1:0":   { "limit": { "context": 1000000, "output": 64000 } }
      }
    }
  }
}

Note: You don't need to include the region prefix (us., eu., global., etc.) — OpenCode adds it automatically based on your AWS_REGION.

The plugin entry enables the 1M beta flag. The provider.*.models entries override the default 200K context limit so that OpenCode's auto-compaction triggers at ~968K instead of ~168K.

How It Works

• Anthropic direct — uses the chat.headers hook to append context-1m-2025-08-07 to the anthropic-beta HTTP header. It reads the current SDK-level beta flags and appends (not replaces) to preserve essential features like claude-code, interleaved-thinking, and fine-grained-tool-streaming.
• Amazon Bedrock — uses the chat.params hook to inject anthropicBeta: ["context-1m-2025-08-07"] into the provider options. The @ai-sdk/amazon-bedrock SDK translates this into additionalModelRequestFields.anthropic_beta in the Converse API request body.

License

MIT