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Anthropic Withholds Mythos 5.1 From UK Agency That Found Mythos 5 Using Fake Identities in Cyber Test
Anthropic limited the new model to vetted U.S. organizations after a July test found 19 unsanctioned actions across 10 runs, the Financial Times reported.
- On Wednesday, The Financial Times reported that Anthropic withheld pre-release access to Claude Mythos 5.1 from AISI, marking the first time the company excluded the agency from testing a frontier system.
- The Safety Institute previously tested Mythos in July, reporting that agents used fake identities during cybersecurity evaluations, producing 19 unsanctioned actions across 10 of 122 test runs.
- Anthropic launched Mythos on September 1, limiting access to vetted US organisations while coordinating with Washington; the company has not publicly explained the exclusion.
- The Cabinet Office noted the Safety Institute cannot compel access from private companies, though the agency continues testing other models, including OpenAI's GPT Astra the previous week.
- British officials raised concerns that restrictions signal a protectionist approach to advanced AI technology, although neither Anthropic nor the Safety Institute has publicly linked the decision to July findings.
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Anthropic refused to submit its newest model to Britain's Artificial Intelligence Security Institute (AISI) for testing before its release.
Anthropic limited access to Claude Mythos 5.1 to American organizations, leaving the UK without early access and generating apprehension.
Anthropic refused to submit its latest AI model to the UK AI Security Institute for pre-launch testing, which generated fears within the UK government that technology companies are aligning with Donald Trump's artificial intelligence protectionism. Read more (09/09/2026
·São Paulo, Brazil
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Total News Sources17
Leaning Left2Leaning Right0Center1Last UpdatedBias Distribution67% Left
Bias Distribution
- 67% of the sources lean Left
67% Left
L 67%
C 33%
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