GoKawiilDario Amodei, co-founder and chief executive officer of Anthropic, at Bloomberg House during the World Economic Forum (WEF) in Davos, Switzerland, on Tuesday, Jan. 20, 2026.
Anthropic on Thursday said it discovered three instances where its Claude artificial intelligence models accessed the internet during an evaluation and "gained unauthorized access to the real systems of three different organizations."
The company said it found these incidents after carrying out a "a large-scale retrospective review" of its cybersecurity evaluations. Anthropic said the review was prompted by a separate but similar security incident that OpenAI disclosed last week.
OpenAI said a combination of its models escaped an isolated testing environment that had very limited internet access. The models chained together a series of vulnerabilities to reach the open web and eventually gain access to Hugging Face, which operates an open-source developer platform.
In the three incidents that Anthropic detected, its models accessed the internet while interacting with a testing environment from one of its third-party evaluation partners called Irregular. The company said that it prompted Claude that it was in a simulation with no internet access, but due to "misunderstanding between us and our evaluation partner, this was not the case, and internet access was available."
The models were then able to breach the impacted organizations by using "basic techniques," like accessing unauthenticated endpoints and exploiting weak passwords. Anthropic did not disclose which three organizations were affected.
"Ultimately, many factors contributed to these incidents, but, consistent with a blameless postmortem culture, we're approaching the fixes as if the responsibility were ours alone," Anthropic said in a release.