Anthropic: No, absolutely not, you may not use third-party harnesses with Claude subs
The Register
February 20, 2026
AI-Generated Deep Dive Summary
Anthropic has updated its legal terms to explicitly prohibit the use of third-party harnesses with Claude subscriptions, aiming to clarify its longstanding policy and protect its revenue model. The company sells subscriptions to its AI platform, which includes access to machine learning models like Opus 4.6 and tools such as Claude Code and Claude Desktop. These tools act as "harnesses," integrating with users' terminals and enhancing the user experience by enabling multi-turn interactions and tool orchestration.
Third-party harnesses, such as OpenAI Codex or Google Antigravity, allow developers to interact with AI models in more engaging ways but can disintermediate model makers like Anthropic. This risks bypassing their subscription-based economics, which offer a cost-effective alternative to pay-as-you-go APIs. By restricting the use of Claude tokens obtained through subscriptions in third-party tools, Anthropic aims to prevent token arbitrage and ensure its revenue model remains sustainable.
The updated terms explicitly state that OAuth tokens from Claude Free, Pro, or Max accounts are only for use within Claude Code and Claude.ai. Using these tokens elsewhere violates their Consumer Terms of Service. This clarification addresses a loophole exploited by third-party tools allowing users to input Claude subscription keys, undermining Anthropic's efforts to maintain control over how its models are accessed.
For tech enthusiasts, this move highlights the ongoing tension between AI platform providers and developers seeking more flexible or cost-effective solutions. Anthropic’s decision underscores the importance of clear legal boundaries in the AI ecosystem, balancing innovation with revenue protection for model makers. This update ensures consistency in company documentation while reinforcing their commitment to maintaining a fair and structured approach to
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Originally published on The Register on 2/20/2026