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AI Choice Engine

Model comparison

GPT-5.5 vs Step 5 Preview

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

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

OpenAI

GPT-5.5

Frontier

vs

StepFun

Step 5 Preview

Frontier

AI model capability comparison
SpecificationGPT-5.5Step 5 Preview
ProviderOpenAIStepFun
TierFrontierFrontier
Context windowWinner: 1.05M1M
Max output128KNot verifiedUnverified
Input / 1M tokens$5Winner: $1
Output / 1M tokens$30Winner: $2.70
WeightsClosedClosed
ParametersNot disclosedUnverified600B total / 27B active MoE (StepFun)
Reasoning levelsnone, low, medium, high, xhighNot verifiedUnverified
Modalitiestext, imagetext, image
API model idgpt-5.5step-5-preview
ReleasedApril 23, 2026September 18, 2026
Artificial Analysis Intelligence Index [xhigh] (2026-09-26)38.4Not verifiedUnverified
Artificial Analysis Intelligence Index (2026-09-26)Not verifiedUnverified43.7
SWE-bench Verified (2026-09-01)82.6Not verifiedUnverified
Terminal-Bench 2.1 (2026-07-27)83.4Not verifiedUnverified
GPQA Diamond (2026-07-27)93.5Not verifiedUnverified
Humanity's Last Exam (2026-04-23)52.2Not 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

GPT-5.5: Standard $5/$30 per MTok; >272K input billed 2x in / 1.5x out. Cached input $0.50/MTok; batch $2.50/$15.

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).

FrontierRecord checked September 26, 2026

GPT-5.5

GPT-5.5 is OpenAI's April 2026 flagship, now two generations back — strong on Terminal-Bench 2.0 (82.7%) with a 1.05M-token context.

Best for

  • Reasoning
  • Agentic coding
  • Long-context work

Watch out

Superseded by GPT-5.6 and then GPT-6 Astra/Sol; still served and widely integrated.

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 $30 for GPT-5.5 — about 11×. 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? GPT-5.5 · Step 5 Preview

Common questions

GPT-5.5 vs Step 5 Preview

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

Is GPT-5.5 or Step 5 Preview cheaper for input?
Step 5 Preview is cheaper at $1 per million input tokens, against $5 for GPT-5.5 — roughly 5.0× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; GPT-5.5 has tiered pricing: Standard $5/$30 per MTok; >272K input billed 2x in / 1.5x out. Cached input $0.50/MTok; batch $2.50/$15. 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 GPT-5.5 or Step 5 Preview cheaper for output?
Step 5 Preview is cheaper at $2.70 per million output tokens, against $30 for GPT-5.5 — roughly 11× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; GPT-5.5 has tiered pricing: Standard $5/$30 per MTok; >272K input billed 2x in / 1.5x out. Cached input $0.50/MTok; batch $2.50/$15. 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, GPT-5.5 or Step 5 Preview?
GPT-5.5 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 GPT-5.5 or Step 5 Preview?
Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. GPT-5.5 suits reasoning; Step 5 Preview suits long-context work on a budget.

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 $5 for GPT-5.5 — a 5x difference at the headline tier.
  • Context: GPT-5.5 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 38.4 (measured 2026-09-26).
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