Model comparison
Claude Mythos 5.1 vs Muse Spark 1.3
Anthropic against Meta, compared on context, price, and verified benchmark results.
Catalog record checked September 5, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below
Anthropic
Claude Mythos 5.1
Frontier
Meta
Muse Spark 1.3
Frontier
| Specification | Claude Mythos 5.1 | Muse Spark 1.3 |
|---|---|---|
| Provider | Anthropic | Meta |
| Tier | Frontier | Frontier |
| Context window | Not verifiedUnverified | 1M |
| Max output | Not verifiedUnverified | 131K |
| Input / 1M tokens | $10 | Winner: $1.25 |
| Output / 1M tokens | $50 | Winner: $4.25 |
| 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-1.3 |
| Released | September 1, 2026 | September 2, 2026 |
| DeepSWE 1.1 (2026-09-02) | Not verifiedUnverified | 75.4 |
| Terminal-Bench 2.1 (2026-09-03) | Not verifiedUnverified | 88.8 |
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
- 2026-09-03: Meta launch table (transcribed by explainx.ai) (Vendor self-report; absent from the official tbench.ai leaderboard)Agentic terminal work: multi-step tasks executed in a sandboxed shell environment. Comparability: comparable with caveat — Scores across Terminal-Bench major versions (v1 vs v2) are NOT comparable; harness configuration (container, time limits) also shifts results.
- 2026-09-02: Meta launch table (Thinking mode: max — self-reported; not broadly available and NOT on the official Datacurve leaderboard)Agentic software engineering: pass@1 on real repo tasks with reported cost per completed task. Comparability: directly comparable
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 1.3: $1.25/$4.25 per MTok on Meta's Model API (cached input $0.15); a $0.10/$0.20 'contributor' tier applies when your data is used for training. Third-party reports put list at $1.50/$7.50 from 2027-01-01 — confirm before long-term commits.
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 1.3
Muse Spark 1.3 is Meta's September 2026 frontier refresh — a self-reported DeepSWE 1.1 field leader at $1.25/$4.25, with a 1M-token context aimed at autonomous agent workflows.
Best for
- Long-horizon coding agents
- Frontier quality below frontier pricing
- Meta ecosystem
Watch out
The headline 75.4% DeepSWE score comes from the 'max' thinking mode, which is not broadly available yet and is pending independent verification. The 131,072 output cap is per third-party API docs — Meta's own spec page does not publish it. Closed weights, unlike Muse Spark 1.1.
When the cheaper one wins
Muse Spark 1.3 is cheaper on output at $4.25 per million tokens against $50 for Claude Mythos 5.1 — about 12×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.
Run the model pickerEvidence 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.
- 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 6 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 1.3: Meta — Introducing Muse Spark 1.3 (accessed 2026-09-03)
- Muse Spark 1.3: Meta developer — Muse Spark pricing ($1.25/$4.25) (accessed 2026-09-03)
- Muse Spark 1.3: VentureBeat — Muse Spark 1.3 best results need a config developers can't broadly use yet (accessed 2026-09-03)
- Muse Spark 1.3: HaiMaker — muse-spark-1.3 (131,072 max output tokens) (accessed 2026-09-05)
- Muse Spark 1.3: Promptfoo — Meta provider docs (muse-spark-1.3 max_tokens ceiling) (accessed 2026-09-05)
Related comparisons
- Claude Fable 5.1 vs Claude Mythos 5.1
- Claude Fable 5.1 vs Muse Spark 1.3
- Claude Fable 5 vs Claude Mythos 5.1
- Claude Fable 5 vs Muse Spark 1.3
- 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 1.3
Common questions
Claude Mythos 5.1 vs Muse Spark 1.3
Answered from the verified figures on this page rather than general guidance.
Is Claude Mythos 5.1 or Muse Spark 1.3 cheaper for input?
Muse Spark 1.3 is cheaper at $1.25 per million input tokens, against $10 for Claude Mythos 5.1 — roughly 8.0× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Mythos 5.1 has tiered pricing: 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 1.3 has tiered pricing: $1.25/$4.25 per MTok on Meta's Model API (cached input $0.15); a $0.10/$0.20 'contributor' tier applies when your data is used for training. Third-party reports put list at $1.50/$7.50 from 2027-01-01 — confirm before long-term commits.
Is Claude Mythos 5.1 or Muse Spark 1.3 cheaper for output?
Muse Spark 1.3 is cheaper at $4.25 per million output tokens, against $50 for Claude Mythos 5.1 — roughly 12× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Mythos 5.1 has tiered pricing: 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 1.3 has tiered pricing: $1.25/$4.25 per MTok on Meta's Model API (cached input $0.15); a $0.10/$0.20 'contributor' tier applies when your data is used for training. Third-party reports put list at $1.50/$7.50 from 2027-01-01 — confirm before long-term commits.
Do Claude Mythos 5.1 and Muse Spark 1.3 support the same reasoning levels?
Claude Mythos 5.1 exposes adaptive, while Muse Spark 1.3 exposes low, medium, high.
Should I use Claude Mythos 5.1 or Muse Spark 1.3?
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 1.3 suits long-horizon coding agents.
Next step
Choosing between them
The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.
- Input price: Muse Spark 1.3 costs $1.25 per 1M tokens versus $10 for Claude Mythos 5.1 — a 8x difference at the headline tier.
Choosing a harness rather than a model — Cursor, Copilot, Claude Code, Windsurf, or Lovable? Compare agentic harnesses · Latest releases.