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stepfun · Balanced

Step 5 Preview

Added Sep 20, 2026

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Use in the app

Step 5 Preview is StepFun's 600B sparse MoE frontier model for production-scale agents, activating 27B parameters per token. It is built for software engineering, long-horizon tool use, research, professional knowledge work, and finance, with native text, image, and video understanding and a 1M-token context window. ⚠️ Note: This model routes through StepFun, so privacy and logging guarantees may be limited.

  • Reasoning
  • Tools
  • Vision
  • Structured output
  • Video input
  • Parallel tools
Input
Text, Images, Video
Output
Text
Reasoning effort
low · medium · high
Discovery tier
Balanced

Pricing

USD per 1M tokens
Input
$1.00
Output
$2.70
Cache read
$0.05

Reference prices as published by the model provider. API example

Specifications

Context window
1M
Max output
65.5K
Average output (7 days)
1.5K tokens
Longer than 86% of 465 models

Side by side

Step 5 Preview compared

Specifications, prices, speed and benchmark scores next to each other. Benchmarks below show every compared model too.

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Step 5 PreviewstepfunThis modelStep 3.5 FlashstepfunRemove
Providerstepfunstepfun
Discovery tierBalancedOpen weights
AddedSep 20, 2026Feb 2, 2026
Limits
Context window1MBest262.14K
Max output65.54K65.54K
Average output1.5K tokens2.4K tokens
Pricing, USD per 1M tokens
Input$1.00$0.10Best
Output$2.70$0.30Best
Cache read$0.05—
Performance
Request success (24h)100.0%100.0%
Benchmark indexes
Intelligence Index43.7Best16.6
Capabilities
ReasoningYesYes
ToolsYesNo
VisionYesNo
Structured outputYesNo
Video inputYesNo
Parallel toolsYesNo
Reasoning effortlow, medium, high—

Public evaluations

Benchmarks

Independent evaluation results, with how each score ranks among the models in the Noumen catalog.

  • Step 5 Preview
  • Step 3.5 Flash

Intelligence Index

  • Step 5 Preview43.7
  • Step 3.5 Flash16.6

Step 5 Preview: Better than 89% of 326 scored models

3.8Catalog models by score55.1

Agentic work

  • AutomationBench-AA

    Workflow automation, penalized for guardrail violations

    • Step 5 Preview: 51.0%
    • Step 3.5 Flash: —

  • AutomationBench-AA tasks completed

    Workflows finished end to end without a guardrail violation

    • Step 5 Preview: 17.7%
    • Step 3.5 Flash: —

  • AA-Briefcasev1.1

    Agentic knowledge work, rated head to head

    • Step 5 Preview: 1,423 Elo
    • Step 3.5 Flash: —

  • GDPval-AAv2.1

    Economically valuable occupational tasks, rated head to head

    • Step 5 Preview: 1,587 Elo
    • Step 3.5 Flash: —

Document reasoning

  • GDP.pdf

    Professional reasoning over PDF documents, all-pass rate

    • Step 5 Preview: 14.8%
    • Step 3.5 Flash: —

  • AA-LCRv1.1

    Reasoning across long documents

    • Step 5 Preview: 88.3%Top
    • Step 3.5 Flash: 50.0%

  • MLCR-AA

    Long-context reasoning over medical records

    • Step 5 Preview: 18.3%
    • Step 3.5 Flash: —

Reasoning and knowledge

  • Humanity’s Last Exam

    Expert-level questions across academic fields

    • Step 5 Preview: 46.5%Top
    • Step 3.5 Flash: 21.1%

  • GPQA Diamond

    Graduate-level science questions

    • Step 5 Preview: —
    • Step 3.5 Flash: 83.1%

  • IFBench

    Following precise output instructions

    • Step 5 Preview: —
    • Step 3.5 Flash: 64.6%

Coding

  • Terminal-Benchv4.0

    Practical software engineering in a terminal

    • Step 5 Preview: 33.3%
    • Step 3.5 Flash: —

  • SciCode

    Scientific computing in Python

    • Step 5 Preview: 58.9%
    • Step 3.5 Flash: —

Legacy evaluations

  • Terminal-Bench Hard

    Earlier terminal task suite

    • Step 5 Preview: —
    • Step 3.5 Flash: 27.3%

  • τ²-Bench Telecom

    Tool use in a customer-support simulation

    • Step 5 Preview: —
    • Step 3.5 Flash: 94.4%

  • AA-LCR (unversioned)

    Long-context reasoning, earlier grading

    • Step 5 Preview: 88.3%Top
    • Step 3.5 Flash: 50.0%

Scores from Artificial Analysis, updated Oct 26, 2026. Artificial Analysis

Live routing data

Performance and reliability

Recent averages across requests routed for this model. Your own speed depends on prompt length, reasoning effort and load.

Prompt cache hits
32.5%
About $0.69 per 1M input tokens with caching
Request success (24h)
100.0%
Reliable

Cache hits are the share of input tokens recently served from a prompt cache across all requests. They are not a forecast of your own hit rate.

Hourly request success · last 72 hoursLowest hour 100.0%
  • Healthy (98% or more)
  • Degraded (90–98%)
  • Down (under 90%)
  • No requests

Developers

Use it through the API

Noumen’s API is OpenAI-compatible: any Chat Completions client works with a base URL and a key.

Read the quickstart
curl https://www.noumen.xyz/api/v1/chat/completions \
  -H "Authorization: Bearer $NOUMEN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "stepfun/step-5-preview",
    "reasoning_effort": "medium",
    "messages": [{ "role": "user", "content": "Explain this stack trace." }]
  }'
import os
from openai import OpenAI

client = OpenAI(base_url="https://www.noumen.xyz/api/v1", api_key=os.environ["NOUMEN_API_KEY"])
reply = client.chat.completions.create(
    model="stepfun/step-5-preview",
    messages=[{"role": "user", "content": "Explain this stack trace."}],
)
print(reply.choices[0].message.content)

stepfun

Other stepfun models, starting with the same family.