Claude Mythos 5

Overview

Claude Mythos 5 is the limited-access counterpart to Claude Fable 5, released June 9, 2026. It is the same underlying model as Fable 5 with the same capability set, but deployed with its safeguards lifted in some areas rather than the full classifiers that gate the generally available version. Because of that, Mythos 5 is not generally available: it is offered in limited availability to approved customers through Project Glasswing, and is the direct successor to Claude Mythos Preview.

Access is initially granted to a small group of vetted cyberdefenders and infrastructure providers, with Anthropic planning a trusted access program for biology to accelerate biomedical research — customers work through their Anthropic, AWS, or Google Cloud account team to be approved. Teams without Glasswing access are directed to Fable 5, the generally available Mythos-class model. Mythos 5 carries the same 1M-token context window, 128k max output tokens, and $10/$50 per-million-token pricing as Fable 5, and shares its adaptive-thinking behavior. Anthropic's alignment assessment reports Mythos 5's misalignment behavior as "similar to Opus 4.8," and it is designated a Covered Model with 30-day data retention.

What's New

Frontier Cybersecurity Capability

Anthropic describes Mythos 5 as having the strongest cybersecurity capabilities of any model in the world. The Glasswing access model exists precisely because lifting safeguards in some areas exposes capability that Anthropic gates behind vetting — Mythos 5 is positioned for sanctioned defensive security research and infrastructure hardening by approved organizations, not open deployment.

~10× Faster Drug Design

In molecular design work, Mythos 5 accelerated protein design workflows by roughly 10× and generated 9 of 14 strong drug candidates in an evaluated set — moving the model from research curiosity toward a practical accelerant for biomedical discovery pipelines run by approved labs.

Autonomous Genomics Research

Mythos 5 conducted autonomous single-cell analysis across 138 species. In one result, a custom machine-learning model it produced outperformed a published model from a Science paper while being roughly 100× smaller — a concrete demonstration of frontier-level scientific reasoning applied end to end rather than as a chat assistant.

Novel Hypothesis Generation

For early-stage research, scientists preferred Mythos 5's novel hypotheses roughly 80% of the time over Opus-class models — reinforcing its positioning as a research collaborator for the hardest discovery work rather than a general-purpose assistant.

Performance & Positioning

Because Mythos 5 and Fable 5 are the same model under the hood, raw capability benchmarks track Fable 5 (frontier-leading FrontierCode score, and stronger long-context memory use than Opus 4.8 in Slay the Spire testing). The distinction is governance, not performance: Mythos 5 trades general availability for safeguards lifted in some areas under a vetted-access program.

Migration Guide

The supported upgrade path is from Claude Mythos Preview to Mythos 5; Anthropic publishes step-by-step migration instructions for existing Glasswing customers. Key points when moving over:

• Same integration model as Fable 5. Adaptive thinking is always on (no disabled mode), the raw chain of thought is never returned, and you control depth with the effort parameter.
• Access is the gate, not the API. Mythos 5 uses the claude-mythos-5 identifier, but availability is controlled through Project Glasswing approval — contact your Anthropic, AWS, or Google Cloud account team.
• Covered Model retention. Mythos 5 carries 30-day data retention and is not available under zero data retention; confirm this fits your compliance posture before migrating sensitive workloads.

Pricing & Plans

Access note: Pricing matches Fable 5, but Mythos 5 cannot be purchased on demand. It is provisioned only to approved Project Glasswing customers. If you need Mythos-class capability without the approval process, Fable 5 delivers the same underlying model with safety classifiers in place.

Best For

• Approved cybersecurity research teams conducting sanctioned defensive security and infrastructure-hardening work
• Infrastructure providers vetted into Project Glasswing for capability that is gated from open deployment
• Selected biomedical and genomics labs — protein design, single-cell analysis, hypothesis generation — if approved under Anthropic's planned trusted biology access program
• Organizations with an Anthropic, AWS, or Google Cloud account team that can sponsor Glasswing approval
• Existing Claude Mythos Preview customers upgrading to the production Mythos 5 model

Everyone else should use Claude Fable 5, which delivers the same underlying model with safety classifiers and full general availability.

FAQ