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Model comparison

Kimi K3 vs Step 5 Preview

Moonshot AI against StepFun, compared on context, price, and verified benchmark results.

Catalog record checked September 26, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below

Moonshot AI

Kimi K3

Frontier · Open weights

vs

StepFun

Step 5 Preview

Frontier

AI model capability comparison
SpecificationKimi K3Step 5 Preview
ProviderMoonshot AIStepFun
TierFrontierFrontier
Context windowWinner: 1.05M1M
Max output1.05MNot verifiedUnverified
Input / 1M tokens$3Winner: $1
Output / 1M tokens$15Winner: $2.70
WeightsOpenClosed
Parameters2.8T (open-weight MoE)600B total / 27B active MoE (StepFun)
Reasoning levelslow, high, maxNot verifiedUnverified
Modalitiestext, image, videotext, image
API model idkimi-k3step-5-preview
ReleasedJuly 16, 2026September 18, 2026
Artificial Analysis Intelligence Index [max] (2026-09-26)43.6Not verifiedUnverified
Artificial Analysis Intelligence Index (2026-09-26)Not verifiedUnverified43.7
Terminal-Bench 2.1 (2026-07-27)88.3Not verifiedUnverified
GPQA Diamond (2026-07-27)93.5Not verifiedUnverified
Humanity's Last Exam (2026-07-27)56Not verifiedUnverified
SWE-bench Verified (2026-09-01)93.4Not verifiedUnverified

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

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

Pricing tiers

Kimi K3: $3/$15 per MTok; cached input $0.30/MTok. max_completion_tokens can be set up to 1,048,576 (default 131,072). Open-weight under the custom Kimi K3 License (not a standard open-source licence). 2.8T MoE with native vision.

Step 5 Preview: $1.00/$2.70 per MTok on the StepFun platform (cache-hit input $0.05); StepFun lists it under Multimodal Reasoning Models and says output tokens include reasoning. No max-output figure is published. StepFun says open weights follow on 2026-10-15. Release date per Artificial Analysis's listing (StepFun's launch page is undated).

FrontierOpen weightsRecord checked September 26, 2026

Kimi K3

Kimi K3 is Moonshot AI's open-weight frontier model — 2.8T MoE, 1M context, tied near the top of open-weight leaderboards.

Best for

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

Watch out

Self-hosting needs large clusters; hosted rates vary.

FrontierRecord checked September 26, 2026

Step 5 Preview

Step 5 Preview is StepFun's new frontier reasoning model — a 1M-context, vision-input API preview that lands near Kimi K3 and GLM 5.3 on the Artificial Analysis index at a lower price.

Best for

  • Long-context work on a budget
  • Chinese + English
  • Early testing before the open-weight drop

Watch out

Preview: weights are promised for 2026-10-15 but not yet released, and its max output is unpublished and the launch benchmarks are vendor-run.

When the cheaper one wins

Step 5 Preview is cheaper on output at $2.70 per million tokens against $15 for Kimi K3 — about 5.6×. 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.

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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, reasoning levels.
  • 1 shared named benchmark (scores match) — Measured on: Artificial Analysis Intelligence Index — scores are equivalent, so the benchmark does not separate the pair.
  • Verified within the last 90 days — Newest catalog check was 2 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? Kimi K3 · Step 5 Preview

Common questions

Kimi K3 vs Step 5 Preview

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

Is Kimi K3 or Step 5 Preview cheaper for input?
Step 5 Preview is cheaper at $1 per million input tokens, against $3 for Kimi K3 — roughly 3.0× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Kimi K3 has tiered pricing: $3/$15 per MTok; cached input $0.30/MTok. max_completion_tokens can be set up to 1,048,576 (default 131,072). Open-weight under the custom Kimi K3 License (not a standard open-source licence). 2.8T MoE with native vision. Step 5 Preview has tiered pricing: $1.00/$2.70 per MTok on the StepFun platform (cache-hit input $0.05); StepFun lists it under Multimodal Reasoning Models and says output tokens include reasoning. No max-output figure is published. StepFun says open weights follow on 2026-10-15. Release date per Artificial Analysis's listing (StepFun's launch page is undated).
Is Kimi K3 or Step 5 Preview cheaper for output?
Step 5 Preview is cheaper at $2.70 per million output tokens, against $15 for Kimi K3 — roughly 5.6× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Kimi K3 has tiered pricing: $3/$15 per MTok; cached input $0.30/MTok. max_completion_tokens can be set up to 1,048,576 (default 131,072). Open-weight under the custom Kimi K3 License (not a standard open-source licence). 2.8T MoE with native vision. Step 5 Preview has tiered pricing: $1.00/$2.70 per MTok on the StepFun platform (cache-hit input $0.05); StepFun lists it under Multimodal Reasoning Models and says output tokens include reasoning. No max-output figure is published. StepFun says open weights follow on 2026-10-15. Release date per Artificial Analysis's listing (StepFun's launch page is undated).
Which has the larger context window, Kimi K3 or Step 5 Preview?
Kimi K3 accepts 1.05M tokens against 1M for Step 5 Preview. This only matters if you routinely send very long documents or large codebases.
Should I use Kimi K3 or Step 5 Preview?
Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. Kimi K3 suits open-weight frontier work; Step 5 Preview suits long-context work on a budget.
Can I self-host Kimi K3 or Step 5 Preview?
Kimi K3 publishes open weights, but self-hosting and third-party provider access depend on the licence, hardware, serving support, and availability. Step 5 Preview 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: Step 5 Preview costs $1 per 1M tokens versus $3 for Kimi K3 — a 3x difference at the headline tier.
  • Context: Kimi K3 takes 1.05M against 1M for Step 5 Preview — only decisive if your prompts approach the smaller window.
  • Measured capability: Step 5 Preview leads Artificial Analysis Intelligence Index 43.7 to 43.6 (measured 2026-09-26).
  • Deployment: Kimi K3 publishes weights you can self-host; the other is API-only.
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