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Model comparison

Step 5 Preview vs Upstage Solar Pro 4

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

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

StepFun

Step 5 Preview

Frontier

vs

Upstage

Upstage Solar Pro 4

Frontier

AI model capability comparison
SpecificationStep 5 PreviewUpstage Solar Pro 4
ProviderStepFunUpstage
TierFrontierFrontier
Context windowWinner: 1M524K
Max outputNot verifiedUnverified128K
Input / 1M tokens$1Winner: $0.30
Output / 1M tokens$2.70Winner: $1.20
WeightsClosedClosed
Parameters600B total / 27B active MoE (StepFun)Not disclosedUnverified
Reasoning levelsNot verifiedUnverifiedlow, medium, high
Modalitiestext, imagetext
API model idstep-5-previewsolar-pro4
ReleasedSeptember 18, 2026August 10, 2026
Artificial Analysis Intelligence Index (2026-09-26)Winner: 43.728.2

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.

  • 2026-09-26
    Artificial Analysis (AA-estimated)

    Composite index blending reasoning, knowledge, and coding evals into one 0–100 score.

    Comparable with caveatOnly same-version scores are comparable. v4.3.2 was rebaselined (the top score fell from 66 on v4.1.1 to ~58), so v4.1.1 figures must not be compared with v4.3.2 figures — check measuredAt.

Pricing tiers

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).

Upstage Solar Pro 4: List $0.30/$1.20 per MTok; cached input $0.06. The 90%-off launch promo ended 2026-09-10. Closed API. 524K context with up to 128K output.

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.

FrontierRecord checked September 26, 2026

Upstage Solar Pro 4

Solar Pro 4 is Upstage's closed flagship with a 524K context at a low $0.30/$1.20 list price.

Best for

  • Long-context
  • Cost-sensitive API
  • Korean + English

Watch out

Closed API; the launch promo has ended, so budget at the $0.30/$1.20 list rate.

When the cheaper one wins

Upstage Solar Pro 4 is cheaper on output at $1.20 per million tokens against $2.70 for Step 5 Preview — about 2.3×. 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. These are standard-tier API rates, excluding batch and cache discounts.

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Evidence confidence: High

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.
  • 2/5 core specs verified on both sides — Not published for at least one side: max output, parameter count, reasoning levels.
  • 1 shared named benchmark with differing scores — Measured on: Artificial Analysis Intelligence Index.
  • 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? Step 5 Preview · Upstage Solar Pro 4

Common questions

Step 5 Preview vs Upstage Solar Pro 4

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

Is Step 5 Preview or Upstage Solar Pro 4 cheaper for input?
Upstage Solar Pro 4 is cheaper at $0.30 per million input tokens, against $1 for Step 5 Preview — roughly 3.3× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; 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). Upstage Solar Pro 4 has tiered pricing: List $0.30/$1.20 per MTok; cached input $0.06. The 90%-off launch promo ended 2026-09-10. Closed API. 524K context with up to 128K output.
Is Step 5 Preview or Upstage Solar Pro 4 cheaper for output?
Upstage Solar Pro 4 is cheaper at $1.20 per million output tokens, against $2.70 for Step 5 Preview — roughly 2.3× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; 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). Upstage Solar Pro 4 has tiered pricing: List $0.30/$1.20 per MTok; cached input $0.06. The 90%-off launch promo ended 2026-09-10. Closed API. 524K context with up to 128K output.
Which has the larger context window, Step 5 Preview or Upstage Solar Pro 4?
Step 5 Preview accepts 1M tokens against 524K for Upstage Solar Pro 4. This only matters if you routinely send very long documents or large codebases.
Should I use Step 5 Preview or Upstage Solar Pro 4?
Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. Step 5 Preview suits long-context work on a budget; Upstage Solar Pro 4 suits long-context.

Next step

Choosing between them

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

  • Input price: Upstage Solar Pro 4 costs $0.30 per 1M tokens versus $1 for Step 5 Preview — a 3.3x difference at the headline tier.
  • Context: Step 5 Preview takes 1M against 524K for Upstage Solar Pro 4 — only decisive if your prompts approach the smaller window.
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