Anthropic cut off OpenAI’s ability to use its API for Anthropic models on Tuesday. The move followed Anthropic’s finding that OpenAI had violated its terms by accessing Anthropic’s tools in prohibited ways.
Christopher Nulty, a spokesperson for Anthropic, said in a statement to WIRED , “Claude Code has become the go-to choice for coders everywhere, and so it was no surprise to learn OpenAI’s own technical staff were also using our coding tools ahead of the launch of GPT-5. Unfortunately, this is a direct violation of our terms of service.”
Under Anthropic’s commercial terms, customers may not develop another product or service, create their own AI models using Anthropic’s platform, or attempt to dissect or replicate its technology .
This adjustment to Claude availability coincides with OpenAI’s internal preparations for GPT-5 , the forthcoming model touted for enhanced coding capabilities.
OpenAI allegedly used custom APIs for Claude access
According to insiders, OpenAI integrated Claude into its proprietary toolchain via custom APIs rather than the usual chat portal. This arrangement enabled OpenAI to assess Claude’s performance on programming and writing tasks, and to evaluate its responses to safety-related queries regarding areas such as CSAM, self-harm, and defamatory content.
The findings were then used to compare Claude against OpenAI’s in-house models and to fine-tune OpenAI’s systems accordingly.
In response, OpenAI’s chief communications officer, Hannah Wong, said “It’s industry standard to evaluate other AI systems to benchmark progress and improve safety. While we respect Anthropic’s decision to cut off our API access, it’s disappointing considering our API remains available to them.”
Nulty also mentioned that granting API access for purposes like benchmarking and safety reviews remains part of standard industry practice. The company has not clarified how the current restriction on Claude access might affect OpenAI’s ongoing evaluations.
API restrictions have long been wielded as leverage in the tech sector.
For instance, Facebook previously cut off Vine (owned by Twitter), and more recently, Salesforce imposed constraints on rival Slack integrations.
Anthropic enacted a comparable measure against the AI code startup Windsurf amid speculation of an OpenAI takeover, but the deal never happened. Anthropic’s chief science officer, Jared Kaplan, told TechCrunch, “I think it would be odd for us to be selling Claude to OpenAI.”
Anthropic to enforce weekly usage caps on Claude code
Anthropic recently revealed plans to introduce weekly caps on Claude Code to reduce continuous background consumption by users.
The company said in an email and on X that the new limits will start on August 28.
These restrictions will affect users on the $20 Pro tier as well as those on the $100 and $200 Max tiers. Existing five-hourly usage quotas will remain unchanged.
Moreover, the update includes two separate weekly quotas: a general usage cap and a model-specific allowance for Claude Opus 4. Max-tier subscribers will have the option to purchase additional capacity at Anthropic’s standard API pricing once they exceed the weekly thresholds.
This adjustment builds on a subdued deployment of usage ceilings for Claude Code implemented earlier this summer.
Claude Code is popular with developers, but Anthropic has had trouble keeping up with demand. Its service had seven major or partial outages last month, likely caused by heavy use from a small group of users.
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