MythosLM

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The Claude Mythos Preview (April 2026)

Access & preview informational Last reviewed Updated

What the Preview was

Before the June 2026 generation, Anthropic ran a limited Mythos Preview in April 2026. It was the public's first sight of a Mythos-class model — the tier above Opus — but "public" is the wrong word: the Preview never reached open sign-up. It was delivered entirely through Project Glasswing.

Who received it

Access was concentrated in cyberdefense and critical-infrastructure organizations, with US-government involvement publicly indicated. The program reached roughly 50 selected organizations. Anthropic has not published a roster, and specific company or country lists circulating elsewhere should be treated as unconfirmed. See Glasswing organizations for what is actually known.

What it cost

Preview participants used Glasswing pricing: about $25 per million input tokens and $125 per million output tokens. That is several times the public Fable 5 pricing introduced later ($10 / $50 per million after its intro period), reflecting the Preview's early, restricted nature. More detail lives in Glasswing pricing.

How it relates to Fable 5 and Mythos 5

The Preview set the stage for the June 9, 2026 release of Fable 5 and Mythos 5, which share one underlying model. Mythos 5 continued the Glasswing-only, classifier-free approach the Preview established, while Fable 5 added safeguards for a public audience.

Frequently asked questions

Was the Mythos Preview available to the public?

No. It was distributed only through Project Glasswing to roughly 50 selected organizations; there was never an open sign-up.

How much did the Preview cost?

Around $25 per million input tokens and $125 per million output tokens — the Glasswing pricing, well above the later public Fable 5 rates.

Which organizations got the Preview?

Roughly 50, concentrated in cyberdefense and critical infrastructure with US-government involvement. Anthropic has not named them, so treat specific lists as unconfirmed.

Sources & further reading

Facts on this page link to their source. Quotes are kept under 15 words and attributed; figures labelled unofficial are third-party until Anthropic publishes system-card numbers.