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Model comparison

Claude Mythos 5.1 vs Muse Spark 1.2

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

Claude Mythos 5.1: profile checked October 25, 2026Muse Spark 1.2: profile checked October 25, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below

Anthropic

Claude Mythos 5.1

Frontier

vs

Meta

Muse Spark 1.2

Frontier

AI model capability comparison
SpecificationClaude Mythos 5.1Muse Spark 1.2
ProviderAnthropicMeta
TierFrontierFrontier
Context window1MWinner: 1.05M
Max output128KNot verifiedUnverified
Input / 1M tokens$10Winner: $1.25
Output / 1M tokens$50Winner: $4.25
WeightsClosedNot verifiedUnverified
ParametersNot verifiedUnverifiedNot verifiedUnverified
Reasoning levelslow, medium, high, xhigh, maxminimal, low, medium, high, xhigh
Modalitiestext, imagetext, image, video, audio, pdf
API model idclaude-mythos-5-1muse-spark-1.2
ReleasedSeptember 1, 2026August 5, 2026

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.

Pricing tiers

Claude Mythos 5.1: Standard USD/MTok input/output $10/$50, matching Fable 5.1; cache reads $0.25, 5-minute writes $12.50, 1-hour writes $20. Batch $5/$25. US-only inference adds 10% to input/output and cache reads/writes on Anthropic-operated routes where supported; Foundry uses US Data Zone Standard. Bedrock and Google-managed Google Cloud have independent regional prices. Access requires verification; the public API ID does not grant entitlement. Retirement not sooner than September 1, 2027 is a minimum commitment, not an announced shutdown. Server-side tools can add usage fees; tool schemas/results and thinking consume billable tokens.

Muse Spark 1.2: Meta Standard USD/MTok input/output $1.25/$4.25, cached $0.15. Separate muse-spark-1.2-contributor $0.10/$0.20, cached $0.002 permits training on submitted content. No long-context premium. Web search adds $2.50/1,000 queries. Standard 3,000 RPM/4M TPM versus Contributor 150 RPM/3M TPM, counted per team rather than API key. Muse Code plan quotas and mode defaults are separate.

FrontierRecord checked October 25, 2026

Claude Mythos 5.1

Claude Fable 5.1's underlying capabilities for organisations verified for cybersecurity or life-sciences research, with different cyber/bio safeguards and access controls.

Best for

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

Watch out

Access requires an applicable verification programme; current primary sources do not establish a universal country eligibility list. Accepting 30-day data retention for safety monitoring is required by default. Adaptive thinking is always on and forced tool use errors. Shared underlying capabilities do not make Fable benchmark results Mythos observations; safeguards, fallback behavior and evaluation setups differ.

FrontierRecord checked October 25, 2026

Muse Spark 1.2

Muse Spark 1.2 is Meta's previous version, still listed on the Model API alongside the 1.3 refresh.

Best for

  • Frontier reasoning
  • Meta ecosystem
  • Agentic work

Watch out

The previous version remains in the public API and Muse Code. Minimal/low/medium/high/xhigh are supported; none returns400 and max is not supported for 1.2. Audio is listed without1.3’s degradation warning. Reasoning shares output budget/billing; hard output cap and exact parameter count remain unverified. Spark Open is a separate native checkpoint, not proof that hosted1.2 has its weights, licence or capabilities.

When the cheaper one wins

Muse Spark 1.2 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 1 day 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 1.2

Common questions

Claude Mythos 5.1 vs Muse Spark 1.2

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

Is Claude Mythos 5.1 or Muse Spark 1.2 cheaper for input?
Muse Spark 1.2 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 USD/MTok input/output $10/$50, matching Fable 5.1; cache reads $0.25, 5-minute writes $12.50, 1-hour writes $20. Batch $5/$25. US-only inference adds 10% to input/output and cache reads/writes on Anthropic-operated routes where supported; Foundry uses US Data Zone Standard. Bedrock and Google-managed Google Cloud have independent regional prices. Access requires verification; the public API ID does not grant entitlement. Retirement not sooner than September 1, 2027 is a minimum commitment, not an announced shutdown. Server-side tools can add usage fees; tool schemas/results and thinking consume billable tokens. Muse Spark 1.2: Meta Standard USD/MTok input/output $1.25/$4.25, cached $0.15. Separate muse-spark-1.2-contributor $0.10/$0.20, cached $0.002 permits training on submitted content. No long-context premium. Web search adds $2.50/1,000 queries. Standard 3,000 RPM/4M TPM versus Contributor 150 RPM/3M TPM, counted per team rather than API key. Muse Code plan quotas and mode defaults are separate.
Is Claude Mythos 5.1 or Muse Spark 1.2 cheaper for output?
Muse Spark 1.2 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 USD/MTok input/output $10/$50, matching Fable 5.1; cache reads $0.25, 5-minute writes $12.50, 1-hour writes $20. Batch $5/$25. US-only inference adds 10% to input/output and cache reads/writes on Anthropic-operated routes where supported; Foundry uses US Data Zone Standard. Bedrock and Google-managed Google Cloud have independent regional prices. Access requires verification; the public API ID does not grant entitlement. Retirement not sooner than September 1, 2027 is a minimum commitment, not an announced shutdown. Server-side tools can add usage fees; tool schemas/results and thinking consume billable tokens. Muse Spark 1.2: Meta Standard USD/MTok input/output $1.25/$4.25, cached $0.15. Separate muse-spark-1.2-contributor $0.10/$0.20, cached $0.002 permits training on submitted content. No long-context premium. Web search adds $2.50/1,000 queries. Standard 3,000 RPM/4M TPM versus Contributor 150 RPM/3M TPM, counted per team rather than API key. Muse Code plan quotas and mode defaults are separate.
Which has the larger context window, Claude Mythos 5.1 or Muse Spark 1.2?
Muse Spark 1.2 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 1.2 support the same reasoning levels?
Claude Mythos 5.1 exposes low, medium, high, xhigh, max, while Muse Spark 1.2 exposes minimal, low, medium, high, xhigh.
Should I use Claude Mythos 5.1 or Muse Spark 1.2?
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 1.2 is a candidate for frontier reasoning. 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 1.2 costs $1.25 per 1M tokens versus $10 for Claude Mythos 5.1 — a 8x difference at the headline tier.
  • Context: Muse Spark 1.2 takes 1.05M against 1M for Claude Mythos 5.1 — only decisive if your prompts approach the smaller window.
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