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Model comparison

Claude Mythos 5.1 vs Muse Spark 1.3

Anthropic against Meta, compared on context, price, and attributed benchmark results.

Recorded profile verification October 2, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below

Anthropic

Claude Mythos 5.1

Frontier

vs

Meta

Muse Spark 1.3

Frontier

AI model capability comparison
SpecificationClaude Mythos 5.1Muse Spark 1.3
ProviderAnthropicMeta
TierFrontierFrontier
Context window1MWinner: 1.05M
Max output128KNot verifiedUnverified
Input / 1M tokens$10Winner: $1.25
Output / 1M tokens$50Winner: $4.25
WeightsClosedClosed
ParametersNot verifiedUnverifiedNot verifiedUnverified
Reasoning levelslow, medium, high, xhigh, maxminimal, low, medium, high, xhigh, max
Modalitiestext, imagetext, image, video, audio, pdf
API model idclaude-mythos-5-1muse-spark-1.3
ReleasedSeptember 1, 2026September 2, 2026
Artificial Analysis Intelligence Index [max] · source date Muse Spark 1.3: 2026-10-01Not verifiedUnverified48
DeepSWE 1.1 · source date Muse Spark 1.3: 2026-09-02Not verifiedUnverified75.4

Dates beside benchmark scores refer to the linked source’s publication or capture date unless that source explicitly states when it measured the result. A shared URL alone does not establish comparable runs; unverified setups are marked. Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.

Benchmark receipts

Where each score comes from, and how far it can be compared across models.

Pricing tiers

Claude Mythos 5.1: Standard $10/$50 per MTok, sharing Fable 5.1's specifications/pricing. Cache reads $0.25; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Invite-only for vetted US organisations; API ID claude-mythos-5-1. Retirement not sooner than September 1, 2027; this is a minimum commitment, not an announced shutdown.

Muse Spark 1.3: Meta Standard $1.25/$4.25 per MTok, cached $0.15; prompts/completions are not used for training. Contributor uses a distinct SKU at $0.10/$0.20, cached $0.002, and permits training on prompts/completions. No long-context premium. Search grounding adds $2.50 per 1,000 queries.

FrontierRecord checked October 1, 2026

Claude Mythos 5.1

Anthropic describes Claude Mythos 5.1 as its 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 for vetted US organisations through trusted access programmes, with 30-day retention required by default for safety monitoring. Adaptive thinking cannot be disabled and forced tool use errors. Shared underlying model does not make Fable benchmark results Mythos observations; safeguards and access differ.

FrontierRecord checked October 2, 2026

Muse Spark 1.3

Muse Spark 1.3 is Meta's September 2026 frontier refresh with a 1M-token context for coding and agent workflows.

Best for

  • Long-horizon coding agents
  • Frontier quality below frontier pricing
  • Meta ecosystem

Watch out

Max effort is Standard Spark 1.3 only; Contributor and Spark 1.2 lack it. None returns HTTP 400; omitted effort is model-determined. Reasoning counts toward output budget and billing. Spark 1.3 audio may degrade; Meta directs audio work to 1.2 or Voice Transcribe. Standard 3,000 RPM/4M TPM versus Contributor 100 RPM/3M TPM quotas apply per team. Exact output cap and parameter count remain unknown. Meta's 75.4% DeepSWE max/mini-swe-agent report is separate from independent xhigh observations.

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. This compares standard short-context token rates, not total cost per accepted task. Include input, cache, context tiers, schedules, retries and review in your pilot.

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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.
  • 3/5 core specs verified on both sides — Not published for at least one side: max output, parameter count.
  • No directly aligned benchmark setup — No benchmark has matching cited sources, source dates, units, effort and recorded run details on both models.
  • Verified within the last 90 days — Older of the two catalog checks was 25 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 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. Estimate both input and output token volume for your workload. These are base rates; Claude Mythos 5.1: Standard $10/$50 per MTok, sharing Fable 5.1's specifications/pricing. Cache reads $0.25; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Invite-only for vetted US organisations; API ID claude-mythos-5-1. Retirement not sooner than September 1, 2027; this is a minimum commitment, not an announced shutdown. Muse Spark 1.3: Meta Standard $1.25/$4.25 per MTok, cached $0.15; prompts/completions are not used for training. Contributor uses a distinct SKU at $0.10/$0.20, cached $0.002, and permits training on prompts/completions. No long-context premium. Search grounding adds $2.50 per 1,000 queries.
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. Estimate both input and output token volume for your workload. These are base rates; Claude Mythos 5.1: Standard $10/$50 per MTok, sharing Fable 5.1's specifications/pricing. Cache reads $0.25; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Invite-only for vetted US organisations; API ID claude-mythos-5-1. Retirement not sooner than September 1, 2027; this is a minimum commitment, not an announced shutdown. Muse Spark 1.3: Meta Standard $1.25/$4.25 per MTok, cached $0.15; prompts/completions are not used for training. Contributor uses a distinct SKU at $0.10/$0.20, cached $0.002, and permits training on prompts/completions. No long-context premium. Search grounding adds $2.50 per 1,000 queries.
Which has the larger context window, Claude Mythos 5.1 or Muse Spark 1.3?
Muse Spark 1.3 accepts 1.05M tokens against 1M for Claude Mythos 5.1. This only matters if you routinely send very long documents or large codebases.
Do Claude Mythos 5.1 and Muse Spark 1.3 support the same reasoning levels?
Claude Mythos 5.1 exposes low, medium, high, xhigh, max, while Muse Spark 1.3 exposes minimal, low, medium, high, xhigh, max.
Should I use Claude Mythos 5.1 or Muse Spark 1.3?
Both are classified in our frontier tier; this editorial grouping does not imply equal capability. Claude Mythos 5.1 is a candidate for cyber-defence research; Muse Spark 1.3 is a candidate for long-horizon coding agents. Compare accuracy, tool reliability, latency and cost on representative tasks.

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.
  • Context: Muse Spark 1.3 takes 1.05M against 1M for Claude Mythos 5.1 — only decisive if your prompts approach the smaller window.
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