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Model comparison

Claude Fable 5 vs Claude Mythos 5.1

Two Anthropic tiers compared on the figures that decide which one a workload actually needs.

Catalog record checked September 3, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below

Anthropic

Claude Fable 5

Frontier

vs

Anthropic

Claude Mythos 5.1

Frontier

AI model capability comparison
SpecificationClaude Fable 5Claude Mythos 5.1
ProviderAnthropicAnthropic
TierFrontierFrontier
Context window1MNot verifiedUnverified
Max output128KNot verifiedUnverified
Input / 1M tokens$10$10
Output / 1M tokens$50$50
WeightsClosedClosed
ParametersNot disclosedUnverifiedcyber/bio research variant of Fable 5.1
Reasoning levelsadaptiveadaptive
Modalitiestext, imagetext, image
API model idclaude-fable-5claude-mythos-5
ReleasedJune 9, 2026September 1, 2026
Artificial Analysis Intelligence Index (2026-08-14)62Not verifiedUnverified

Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.

Benchmark receipts

  • 2026-08-14: Artificial Analysis (with fallback)Composite index blending reasoning, knowledge, and coding evals into one 0–100 score. Comparability: directly comparable — AA occasionally rebaselines the index scale between snapshots — a score captured on one date is only comparable to same-snapshot scores (check measuredAt).

Pricing tiers: Claude Fable 5: Standard $10/$50 per MTok; cache reads 10% of base input. Sibling Claude Mythos 5 is invite-only cyber-defense. Access briefly suspended 2026-06-12, redeployed 2026-07-01. · Claude Mythos 5.1: Starts at $10/$50 per MTok — priced with Fable 5.1, which shares the same underlying model. API id claude-mythos-5 replaced the deprecated claude-mythos-preview.

FrontierRecord checked September 3, 2026

Claude Fable 5

Claude Fable 5 is Anthropic's next-generation intelligence model for long-running agents, topped LiveBench until the 5.1 refresh.

Best for

  • Long-running agents
  • Frontier reasoning
  • Enterprise work

Watch out

Most expensive Anthropic tier at $10/$50; verify the cost is justified by the task.

FrontierRecord checked September 3, 2026

Claude Mythos 5.1

Claude Mythos 5.1 is Anthropic's most capable model for cybersecurity and biology research — the Fable 5.1 model with fewer cyber/bio safeguards, restricted to vetted US organisations.

Best for

  • Cyber-defence research
  • Biology research
  • Claude Security workloads

Watch out

Invite-only (vetted US organisations, verification programmes); 30-day data retention applies by default. Same underlying model as Fable 5.1 — most teams should just use Fable.

When the cheaper one wins

Both charge $50 per million output tokens at standard rates, so output price is not the split. Prefer the row whose “best for” line matches the job, then confirm the live vendor rate.

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Evidence confidence: Medium

How strong and complete the evidence behind this comparison is — not a prediction of which model is better.

  • Pricing verified on both sides — Input and output rates are verified for both models.
  • 2/5 core specs verified on both sides — Not published for at least one side: context window, max output, parameter count.
  • No shared named benchmark — No benchmark has been measured on both models.
  • Verified within the last 90 days — Newest catalog check was 8 days ago.
  • Both models carry source citations — Each side has at least two catalog sources on record.

Source receipts

Each catalog figure was checked against the provider or an independent second source on the date shown.

Related comparisons

Diving deeper on one model? Claude Fable 5 · Claude Mythos 5.1

Common questions

Claude Fable 5 vs Claude Mythos 5.1

Answered from the verified figures on this page rather than general guidance.

Is Claude Fable 5 or Claude Mythos 5.1 cheaper for input?

Both cost $10 per million input tokens at standard rates, so input price is not a deciding factor between them.

Is Claude Fable 5 or Claude Mythos 5.1 cheaper for output?

Both cost $50 per million output tokens at standard rates, so output price is not a deciding factor between them.

Do Claude Fable 5 and Claude Mythos 5.1 support the same reasoning levels?

Yes — both accept the same effort settings: "adaptive". Higher effort costs more and takes longer, so start low and raise it only where output quality actually improves.

Should I use Claude Fable 5 or Claude Mythos 5.1?

Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. Claude Fable 5 suits long-running agents; Claude Mythos 5.1 suits cyber-defence research.

Next step

Choosing between them

The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.

These two models match on every verified catalog figure — the decision comes down to provider preference, availability, and workload fit rather than published numbers.

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