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Model comparison

Claude Mythos 5.1 vs Kimi K3

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

Recorded profile verification October 1, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below

Anthropic

Claude Mythos 5.1

Frontier

vs

Moonshot AI

Kimi K3

Frontier · Open weights

AI model capability comparison
SpecificationClaude Mythos 5.1Kimi K3
ProviderAnthropicMoonshot AI
TierFrontierFrontier
Context window1MWinner: 1.05M
Max output128KWinner: 1.05M
Input / 1M tokens$10Winner: $3
Output / 1M tokens$50Winner: $15
WeightsClosedOpen
ParametersNot verifiedUnverified2.8T total / 104B active (MoE)
Reasoning levelslow, medium, high, xhigh, maxlow, high, max
Modalitiestext, imagetext, image, video
LicenseNot verifiedUnverifiedKimi K3 License (custom)
API model idclaude-mythos-5-1kimi-k3
ReleasedSeptember 1, 2026July 16, 2026
Artificial Analysis Intelligence Index [max] · source date Kimi K3: 2026-10-01Not verifiedUnverified44
Terminal-Bench 2.1 [max] · source date Kimi K3: 2026-10-01Not verifiedUnverified88.3
GPQA Diamond [max] · source date Kimi K3: 2026-10-01Not verifiedUnverified93.5
Humanity's Last Exam [max] · source date Kimi K3: 2026-10-01Not verifiedUnverified56
SWE-bench Verified · source date Kimi K3: 2026-10-01Not verifiedUnverified93.4

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.

Kimi K3: $3/$15 per million input/output tokens; cached input $0.30. Cache writes add $3/MTok for 5-minute TTL or $6/MTok for 1-hour TTL; hits refresh TTL without another write charge. API access requires a successful top-up of at least $1. max_completion_tokens defaults to 131,072 and can be set up to 1,048,576. Kimi K3 uses a custom license; self-hosting has compute costs.

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.

FrontierOpen weightsRecord checked October 1, 2026

Kimi K3

Kimi K3 is Moonshot AI's open-weight multimodal 2.8T/104B MoE model with a 1,048,576-token context.

Best for

  • Open-weight frontier work
  • Long-context
  • Multimodal

Watch out

Thinking is always on; preserve complete assistant reasoning/tool history. Vision input requires base64 or ms:// rather than public image URLs, and temperature/top_p/n/penalties are fixed. Current docs discourage production web-search use. The custom licence requires an agreement for Model-as-a-Service businesses above $20M aggregate licensee/affiliate revenue over consecutive 12 months; commercial products above 100M monthly active users or $20M monthly revenue require Kimi K3 UI attribution. Internal use and official/certified serving routes have separate exemptions. July 16 is Kimi Code's release date, distinct from weights publication.

When the cheaper one wins

Kimi K3 is cheaper on output at $15 per million tokens against $50 for Claude Mythos 5.1 — about 3.3×. 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.
  • 4/5 core specs verified on both sides — Not published for at least one side: 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 · Kimi K3

Common questions

Claude Mythos 5.1 vs Kimi K3

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

Is Claude Mythos 5.1 or Kimi K3 cheaper for input?
Kimi K3 is cheaper at $3 per million input tokens, against $10 for Claude Mythos 5.1 — roughly 3.3× 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. Kimi K3: $3/$15 per million input/output tokens; cached input $0.30. Cache writes add $3/MTok for 5-minute TTL or $6/MTok for 1-hour TTL; hits refresh TTL without another write charge. API access requires a successful top-up of at least $1. max_completion_tokens defaults to 131,072 and can be set up to 1,048,576. Kimi K3 uses a custom license; self-hosting has compute costs.
Is Claude Mythos 5.1 or Kimi K3 cheaper for output?
Kimi K3 is cheaper at $15 per million output tokens, against $50 for Claude Mythos 5.1 — roughly 3.3× 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. Kimi K3: $3/$15 per million input/output tokens; cached input $0.30. Cache writes add $3/MTok for 5-minute TTL or $6/MTok for 1-hour TTL; hits refresh TTL without another write charge. API access requires a successful top-up of at least $1. max_completion_tokens defaults to 131,072 and can be set up to 1,048,576. Kimi K3 uses a custom license; self-hosting has compute costs.
Which has the larger context window, Claude Mythos 5.1 or Kimi K3?
Kimi K3 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 Kimi K3 support the same reasoning levels?
Claude Mythos 5.1 exposes low, medium, high, xhigh, max, while Kimi K3 exposes low, high, max.
Should I use Claude Mythos 5.1 or Kimi K3?
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; Kimi K3 is a candidate for open-weight frontier work. Compare accuracy, tool reliability, latency and cost on representative tasks.
Can I self-host Claude Mythos 5.1 or Kimi K3?
Kimi K3 publishes open weights, but self-hosting and third-party provider access depend on the licence, hardware, serving support, and availability. Claude Mythos 5.1 is a closed model whose supported access paths are controlled by its provider.

Next step

Choosing between them

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

  • Input price: Kimi K3 costs $3 per 1M tokens versus $10 for Claude Mythos 5.1 — a 3.3x difference at the headline tier.
  • Context: Kimi K3 takes 1.05M against 1M for Claude Mythos 5.1 — only decisive if your prompts approach the smaller window.
  • Deployment: Kimi K3 publishes weights you can self-host; the other is API-only.
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