Anthropic: No, absolutely not, you may not use third-party harnesses with Claude subs

Anthropic this week revised its legal terms to clarify its policy forbidding the use of third-party harnesses with Claude subscriptions, as the AI biz attempts to shore up its revenue model.

Anthropic sells subscriptions to its Claude platform, which provides access to a family of machine learning models (e.g. Opus 4.6), and associated tools like Claude Code, a web-based interface at Claude.ai, and the Claude Desktop application, among others.

Claude Code is a harness or wrapper – it integrates with the user's terminal and routes prompts to the available Claude model in conjunction with other tools and a control loop that, together, make it what Anthropic calls an agentic coding tool.

Many other tools serve as harnesses for models, such as OpenAI Codex, Google Antigravity, Manus (recently acquired by Meta), OpenCode, Cursor, and Pi (the harness behind OpenClaw). 

Harnesses exist because interacting with a machine learning model ...