---
format: "aidr-story-markdown/v1"
id: "4741fa9295ee47468900eeb6e514be1f30f7e52c04bc33727ac3fbc6c44928cc"
canonical_url: "https://aidr.today/4741fa92?lang=en"
title: "Anthropic Blocks UK AISI From Mythos 5.1 in First Model Test Exclusion"
lang: "en"
requested_lang: "en"
available_langs: ["en","vi"]
translation_fallback: null
fallback_fields: []
published_at: "2026-09-09T08:43:58.000Z"
category: "Regulation"
topics: ["anthropic","claude","regulation","safety","uk","frontier-models","multi-agent","open-source"]
source_urls: ["https://huggingnews.com/ai/anthropic-blocks-uk-aisi-from-mythos-51-in-first-model-test-exclusion-c1657799","https://x.com/FT/status/2097545542955901020","https://x.com/Techmeme/status/2097570891689583094","https://x.com/wallstengine/status/2097570621190496488","https://news.ycombinator.com/item?id=49623306","https://www.politico.eu/article/anthropic-openai-researcher-jacob-coxon-warns-ai-could-kill-humans/","https://huggingnews.com/ai/anthropic-bars-uk-ai-security-institute-from-mythos-51-tests-for-first-t-28ebacbf"]
summary: "Pre-release access to the Claude Mythos 5.1 model was restricted to vetted US organizations, shutting out Britain's AI Security Institute from early safety reviews. This represents the first instance of the UK agency being denied the opportunity to evaluate an Anthropic frontier model before its official public release. The decision has sparked concerns within the UK government that US AI developers are adopting protectionist stances to keep control of model testing and technological advantages. The AI Security Institute typically collaborates with leading global labs to identify risks associated with new large-scale AI systems prior to their deployment."
---

# Anthropic Blocks UK AISI From Mythos 5\.1 in First Model Test Exclusion

> [Open the canonical story](<https://aidr.today/4741fa92?lang=en>)

**Published:** 2026-09-09T08:43:58.000Z
**Category:** Regulation
**Topics:** anthropic, claude, regulation, safety, uk, frontier\-models, multi\-agent, open\-source

## Summary

Pre\-release access to the Claude Mythos 5\.1 model was restricted to vetted US organizations, shutting out Britain's AI Security Institute from early safety reviews\. This represents the first instance of the UK agency being denied the opportunity to evaluate an Anthropic frontier model before its official public release\. The decision has sparked concerns within the UK government that US AI developers are adopting protectionist stances to keep control of model testing and technological advantages\. The AI Security Institute typically collaborates with leading global labs to identify risks associated with new large\-scale AI systems prior to their deployment\.

## Sources

- [Story source](<https://huggingnews.com/ai/anthropic-blocks-uk-aisi-from-mythos-51-in-first-model-test-exclusion-c1657799>)
- [Story source](<https://x.com/FT/status/2097545542955901020>)
- [Supporting source](<https://x.com/Techmeme/status/2097570891689583094>)
- [Supporting source](<https://x.com/wallstengine/status/2097570621190496488>)
- [Discussion](<https://news.ycombinator.com/item?id=49623306>)
- [Story source](<https://www.politico.eu/article/anthropic-openai-researcher-jacob-coxon-warns-ai-could-kill-humans/>)
- [Story source](<https://huggingnews.com/ai/anthropic-bars-uk-ai-security-institute-from-mythos-51-tests-for-first-t-28ebacbf>)