Model comparison
Claude Mythos 5.1 vs Muse Spark 1.2
Anthropic against Meta, compared on context, price, and verified benchmark results.
Catalog record checked September 3, 2026Individual provider fields may changeEvidence confidence: Insufficient data — see receipts below
Anthropic
Claude Mythos 5.1
Frontier
Meta
Muse Spark 1.2
Frontier
| Specification | Claude Mythos 5.1 | Muse Spark 1.2 |
|---|---|---|
| Provider | Anthropic | Meta |
| Tier | Frontier | Frontier |
| Context window | Not verifiedUnverified | 1M |
| Max output | Not verifiedUnverified | Not verifiedUnverified |
| Input / 1M tokens | $10 | Not verifiedUnverified |
| Output / 1M tokens | $50 | Not verifiedUnverified |
| Weights | Closed | Closed |
| Parameters | cyber/bio research variant of Fable 5.1 | Meta frontier model |
| Reasoning levels | adaptive | low, medium, high |
| Modalities | text, image | text, image |
| API model id | claude-mythos-5 | muse-spark-1.2 |
| Released | September 1, 2026 | August 5, 2026 |
| Artificial Analysis Intelligence Index (2026-08-14) | Not verifiedUnverified | 57 |
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 AnalysisComposite 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 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. · Muse Spark 1.2: Closed-weights; served via Meta's Model API. Not open-weight.
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.
Muse Spark 1.2
Muse Spark 1.2 is Meta's closed frontier model until the 1.3 refresh (2026-09-02) — still served and ranked in the LMArena text top 10 as of mid-2026.
Best for
- Frontier reasoning
- Meta ecosystem
- Agentic work
Watch out
Closed-weights (unlike Llama 4); Meta's post-Llama-4 frontier branding.
When the cheaper one wins
One of these rows is missing a verified output price, so this page will not name a cheaper winner. Run the model picker against the actual job instead of guessing.
Run the model pickerEvidence confidence: Insufficient data
How strong and complete the evidence behind this comparison is — not a prediction of which model is better. Hard limitations apply: missing pricing; evidence too sparse.
- Pricing incomplete — No verified token pricing for Muse Spark 1.2.
- 3/5 core specs verified on both sides — Not published for at least one side: context window, max output.
- 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.
- Claude Mythos 5.1: Anthropic — Claude Mythos (accessed 2026-09-03)
- Claude Mythos 5.1: Anthropic — model deprecations (claude-mythos-5) (accessed 2026-09-03)
- Muse Spark 1.2: Meta — Muse (accessed 2026-08-29)
- Muse Spark 1.2: Muse version tracking (accessed 2026-08-29)
Related comparisons
- Claude Fable 5.1 vs Claude Mythos 5.1
- Claude Fable 5.1 vs Muse Spark 1.2
- Claude Fable 5 vs Claude Mythos 5.1
- Claude Fable 5 vs Muse Spark 1.2
- Claude Haiku 4.5 vs Claude Mythos 5.1
- Claude Mythos 5.1 vs Claude Opus 5
Diving deeper on one model? Claude Mythos 5.1 · Muse Spark 1.2
Common questions
Claude Mythos 5.1 vs Muse Spark 1.2
Answered from the verified figures on this page rather than general guidance.
Do Claude Mythos 5.1 and Muse Spark 1.2 support the same reasoning levels?
Claude Mythos 5.1 exposes adaptive, while Muse Spark 1.2 exposes low, medium, high.
Should I use Claude Mythos 5.1 or Muse Spark 1.2?
Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. Claude Mythos 5.1 suits cyber-defence research; Muse Spark 1.2 suits frontier reasoning.
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.
Choosing a harness rather than a model — Cursor, Copilot, Claude Code, Windsurf, or Lovable? Compare agentic harnesses · Latest releases.