Corrected: Introducing Claude Fable 5.1 and Claude Mythos 5.1

ClaudeNew modelConfirmed

Correction: Updated on 4 Oct: this was a launch on 1 Sep, not an update. Fable's price cut covers reused information on plans billed by usage. Mythos is limited to approved US cyberdefense and life sciences organizations.

Anthropic launched Claude Fable 5.1 and Claude Mythos 5.1 for coding, knowledge work and long-running tasks.

Fable now costs less when it reuses information it has already processed on plans billed by usage.
Mythos uses the same underlying model with different safeguards and is limited to approved organizations.

Who can use it: Fable is generally available, including the Claude API and major cloud platforms. Mythos is restricted to vetted US organizations in cyberdefense and life sciences.
When: Launched September 1, 2026, per Anthropic's platform release notes. Enterprise Frontier Safeguards arrive in phases later in the fall; no exact date is given.

Anthropic official announcement · Claude Platform release notes Announced 2026-09-01 · date only

Read the official announcement for access details. Availability can depend on your plan, region or workplace settings.

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