Difference from Fable 5.1
Mythos 5.1 is not a "smarter" standalone model — it is the same underlying model as Fable 5.1 with different safeguards applied.
| Claude Fable 5.1 | Claude Mythos 5.1 | |
|---|---|---|
| Underlying model | Same | Same |
| Availability | General (API, Claude.ai, etc.) | Trusted access only |
| Safeguards | Standard (production) | Relaxed in cyber & life sciences |
| Eligibility | All users | Vetted orgs (currently US only) |
| API ID | claude-fable-5-1 | No public API (application required) |
Source: Anthropic announcement (verified 2026-09-01). "Claude Fable 5.1 and Claude Mythos 5.1 are the same model, but with different levels of safeguards."
Trusted Access Programs
Access to Mythos 5.1 is rolling out through the verification programs below — LSVP is already underway, while CVP will add Mythos-class support soon.
🔐 Cyber Verification Program (CVP)
Currently provides access to certain Opus- and Sonnet-class models with reduced cyber safeguards for defensive security work. Mythos-class models will be added in the near future. Apply to join the CVP →
🧬 Life Sciences Verification Program (LSVP)
Lets life-sciences professionals use Mythos 5.1 with safeguards designed for professional R&D (all other safeguards remain). Enrolled its first participants in partnership with the US government; plans to expand to the broader life-sciences community.
※ Currently limited to US organizations. Anthropic is coordinating with the US government to expand to a broader set of domestic and international partners.
Source: Anthropic announcement (Trusted access for Claude Mythos 5.1)
Performance & Specs
Since the underlying model is identical to Fable 5.1, specs (1M context, 128K output) are shared. Safeguard differences produce small gaps on some benchmarks.
| Benchmark | Mythos 5.1 | Fable 5.1 |
|---|---|---|
| Agentic coding — Terminal-Bench 4.0 | 60.9% | 55.8% |
Anthropic attributes this gap to tasks where earlier, less precise cyber safeguards intervened, and expects the difference to shrink with today's safeguard improvements.
Source: Anthropic announcement (verified 2026-09-01). See the Fable 5.1 page for full specs.
Pricing
Mythos 5.1 is a limited-availability model, but its pricing is published on Anthropic's official pricing page (platform.claude.com). Standard rates match Fable 5.1.
| Tier | Input | 5m Cache Write | 1h Cache Write | Cache Read | Output | Notes |
|---|---|---|---|---|---|---|
| Standard | $10.00 | $12.50 | $20.00 | $0.25 | $50.00 | Same as Fable 5.1. Batch $5/$25 |
📌 Access requires trusted-access vetting
- Pricing is public, but Mythos 5.1 is not freely available as a standard self-service API. Access requires vetting/invitation through CVP or LSVP.
Source: platform.claude.com/docs/en/about-claude/pricing (verified 2026-09-01; listed as "Claude Mythos 5.1 (limited availability)")
Claude Security is now powered by Mythos 5.1
Anthropic's Claude Security product — which scans codebases for vulnerabilities and suggests patches for human review — is now also powered by Claude Mythos 5.1. Direct Mythos 5.1 access is limited to vetted cyberdefenders and life-science professionals; check Anthropic's guidance for Claude Security availability and terms.
Source: Anthropic announcement (verified 2026-09-01)
General users: use Fable 5.1
Mythos 5.1 requires an application. For normal coding and knowledge work, the generally available Fable 5.1 is what you want.
→ Claude Fable 5.1 deep dive📊 Full Pricing Comparison · 🗓️ Release Timeline · 🔗 Anthropic Announcement
⚠️ Disclaimer
- Information verified against Anthropic's official pages (anthropic.com / platform.claude.com) on 2026-09-01. Subject to change without notice.
- Mythos 5.1 eligibility and pricing are application-based; confirm directly with Anthropic.
- This site is informational only. Not affiliated with any provider.