News · 2026-06-26

The US government quietly lets Anthropic turn its most powerful model back on

On June 12, Anthropic shut off its two most capable models, Fable 5 and Mythos 5, for every customer including its own foreign-national employees, to comply with a US government directive. Today, the Commerce Department sent Anthropic a letter clearing Mythos 5 for release to more than a hundred vetted US institutions, including large companies and government agencies. The letter addresses Mythos, the stronger model, and stays silent on Fable, the weaker sibling, though talks on Fable continue.

Key facts

• What: Two weeks after ordering it switched off, Washington cleared Anthropic's Mythos 5 for release to more than a hundred trusted US institutions, a notable de-escalation.
• When: 2026-06-26
• Primary source: read the source

The original block stemmed from capability, not politics. During a security exercise Anthropic calls Project Glasswing, Mythos reportedly found weaknesses in highly sensitive classified US government computer systems — and did so fast. A senator described the tool, in a June hearing, as breaking into almost all of the relevant classified systems in hours rather than weeks, a characterization attributed to a senior military cyber official and reported by CNBC. The timeline is documented through Anthropic's access update and the original Fable 5 and Mythos 5 announcement, with reporting from CNBC and Semafor. This continues a tracked story: when the US government banned Anthropic's most powerful AI model and how that ban started redrawing the AI map.

With the Commerce Department's letter, Mythos 5 may now go to a vetted list of institutions, provided appropriate safeguards are in place. Anthropic has committed to working with the government on protocols and standards. A group of more than a hundred cybersecurity executives had pushed for exactly this outcome, arguing that pulling a powerful cyber-defense tool off the board mainly helps US adversaries.

The same capability that makes Mythos dangerous also makes it valuable for defense. A model that can find weaknesses in classified systems in hours is precisely the tool a defender wants on their own security team — identifying which locks to replace before an adversary tries them. The government's first instinct was to remove the tool entirely; the second, calmer decision was to let a short list of trusted institutions hire it, under supervision.

Read alongside today's news that OpenAI launched GPT-5.6 under government vetting, a new regime is taking shape in which the US government decides, model by model and partner by partner, who gets frontier AI. Both leading labs now operate inside a clearance process — a profound shift from the open sign-up era that puts a premium on being on the approved list. It also sharpens the appeal of open-weight models for everyone outside the circle, since no government letter can switch off a model you have already downloaded.

A de-escalation is not a resolution. Anthropic publicly objected to the lack of transparency in how the original block was issued, asking that such decisions rest on a clear, fair, technically grounded statutory process rather than an opaque directive. Today's letter resolves one model for one list of customers, but the underlying questions remain unanswered: who is on the list and why, what the safeguards actually require, and what happens the next time a model proves too good at breaking into things. The locksmith is back to work, but the rules of the job are still being written in real time.

Primary source, verified: read the paper →

Ground Truth. (2026, June 26). The US government quietly lets Anthropic turn its most powerful model back on. Ground Truth. https://groundtruth.day/news/mythos-5-released-to-trusted-partners.html

@misc{groundtruth:mythos-5-released-to-trusted-partners,
  title  = {The US government quietly lets Anthropic turn its most powerful model back on},
  author = {{Ground Truth}},
  year   = {2026},
  month  = {jun},
  url    = {https://groundtruth.day/news/mythos-5-released-to-trusted-partners.html}
}

Topics: anthropic · mythos-5 · regulation · cybersecurity · export-controls