Anthropic says it thwarted attempts by rogue elements to use its AI models for “malicious activity” that could support the development of biological weapons.

The company disclosed this in its latest threat intelligence report published on Thursday, highlighting five cases in which bad actors attempted to use some of Anthropic’s A.I. models to manufacture biological weapons.

“Results from evaluations of older models (for example Claude Opus 4 and Claude Sonnet 4.5, from 2025) clearly showed that these models were well below the threshold where they could meaningfully assist a sophisticated user in carrying out dangerous biological research,” said Anthropic.

In the first case, Anthropic said a reseller platform used its models to circumvent regional restrictions and serve virologists working on a state-sponsored grant to pursue chikungunya gain-of-function research, later routing refused prompts to models with more permissive safeguards.

Case two stated that a researcher in an unsupported region spent weeks planning avian influenza mammalian-adaptation experiments with Claude, while a reseller in the third case used the Opus 5 model to draft an orthopoxvirus immune-evasion grant application for 12 customers in about an hour.

In case number four,  Anthropic alleged that “a state-supported researcher built a venom peptide atlas and generative optimisation pipeline of molecules directed at paralytic and analgesic targets,” while the researcher in the final case computationally redesigned toxins for a national programme.

The researcher subsequently asked Claude to keep the agents’ identities deliberately vague in progress reports.

Anthropic, however, noted that the five cases are only an evaluation of its models’ capabilities and there was no concrete evidence that they could ever be used in developing biological weapons.

“Although evaluations are useful in that they provide evidence of capability, they cannot concretely demonstrate that such capability would ever be used to develop biological weapons in the real world,” the company stated.