Overview

Identity

Identity block not returned by the API for this entity.

Openness

Openness not classified yet — no sourced evidence to place this model in the ontology.

Key facts

Release date: Source:OpenRouter public model & pricing listingT2observed 13 h agomedium
Status: Source:Artificial AnalysisT2observed 11 h agomedium
Openrouter id: Source:OpenRouter public model & pricing listingT2observed 13 h agomedium

Architecture

Hugging Face repo: Source:OpenRouter public model & pricing listingT2observed 13 h agomedium

Capabilities

Modalities

Modalities: text
Input: text
Output: text

Capabilities

Tool calling
Yes
OpenRouter public model & pricing listing · T2
Structured output
No
OpenRouter public model & pricing listing · T2
Reasoning
Yes
OpenRouter public model & pricing listing · T2
Vision
Unavailable
Audio
Unavailable
Fine-tuning available
Unavailable

Context window: Source:OpenRouter public model & pricing listingT2observed 10 h agomedium
Max output: Source:OpenRouter public model & pricing listingT2observed 13 h agomedium

Benchmarks6

Compare with another model →

Comparable same task and conditions · Partially comparable same task, conditions differ (effort, temperature, judge) · Not comparable different variant or metric

No benchmark results recorded

Results appear when a tier 1–3 source publishes them; we never copy scores without a source.

Providers & Pricing1

All offers in the price terminal →

Current prices per 1M tokens
Provider	Input / 1M	Output / 1M	Cached in	Batch in / out	Context	Observed	Source
OpenRouterstepfun/step-3.5-flash	$0.10	$0.30	—	—	262.1K	6 h ago	openrouter.aiT2

USD per 1M tokens as published by each provider (USD). Rows are append-only: every change is kept in the history below.

Price history

Step lines per provider; amber markers are recorded changes. Click a marker or a row for the evidence behind that price.

Output price · USD / 1M tokens 1 provider

OpenRouter

OpenRouterfirst observed $0.3011 Sept 2026

Input price · USD / 1M tokens 1 provider

OpenRouter

OpenRouterfirst observed $0.1011 Sept 2026

Lineage

Open in Graph →

Explicit derived_from / fine_tuned_from / distilled_from relations stated by sources; artifacts collapsed by kind.

Timeline10

Full timeline →

12 Sept 2026
Context window changedModelStep 3.5 FlashStepFun
Step 3.5 Flash: context length changed from 256000 to 262144
Context window256K tokens→262.1K tokensopenrouter
openrouter.ai
11 Sept 2026
Benchmark resultModelStep 3.5 FlashStepFun
Step 3.5 Flash scores 27.27% on Terminal-Bench
artificial_analysis
artificialanalysis.ai
11 Sept 2026
Benchmark resultModelStep 3.5 FlashStepFun
Step 3.5 Flash scores 94.44% on τ²-bench
artificial_analysis
artificialanalysis.ai
11 Sept 2026
Benchmark resultModelStep 3.5 FlashStepFun
Step 3.5 Flash scores 64.56% on IFBench
artificial_analysis
artificialanalysis.ai
11 Sept 2026
Benchmark resultModelStep 3.5 FlashStepFun
Step 3.5 Flash scores 21.13% on Humanity's Last Exam
artificial_analysis
artificialanalysis.ai
11 Sept 2026
Benchmark resultModelStep 3.5 FlashStepFun
Step 3.5 Flash scores 83.13% on GPQA
artificial_analysis
artificialanalysis.ai
11 Sept 2026
Benchmark resultModelStep 3.5 FlashStepFun
Step 3.5 Flash scores 16.62 on Artificial Analysis Intelligence Index
artificial_analysis
artificialanalysis.ai
11 Sept 2026
Context window changedModelStep 3.5 FlashStepFun
Step 3.5 Flash: context length changed from 262144 to 256000
Context window262.1K tokens→256K tokensartificial_analysis
artificialanalysis.ai
29 Jan 2026
New modelModelStep 3.5 FlashStepFun
New model: Step 3.5 Flash (StepFun)
openrouter
openrouter.ai
11 Sept 2026
Listed by providerModelStep 3.5 FlashStepFun
OpenRouter lists Step 3.5 Flash at $0.1 in / $0.3 out per 1M tokens
openrouter
openrouter.ai

Change history18

Temporal, append-only claims: a new observation closes the previous claim instead of overwriting it. Rewind the record with the as-of picker.

Viewing AI Atlas as of 12 Mar 2026 — attributes exactly as the atlas knew them on that day; later corrections are not shown.

Back to today →

Step 3.5 Flash was not yet in AI Atlas on 12 Mar 2026

First seen 11 Sept 2026. Nothing is inferred backwards: no attribute is shown for dates before the first observation.

18 claims · 16 properties

Release daterelease_date1

Claim history for Release date
Value	Valid from → to	Status	Source	Confidence	Extractor
29 Jan 2026	11 Sept 2026 21:10 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic

Statusstatus1

Claim history for Status
Value	Valid from → to	Status	Source	Confidence	Extractor
deprecated	11 Sept 2026 22:42 UTC → current	current	Artificial AnalysisT2	medium	deterministic

Opennessopenness1

Claim history for Openness
Value	Valid from → to	Status	Source	Confidence	Extractor
open-weights	11 Sept 2026 22:42 UTC → current	current	Artificial AnalysisT2	medium	deterministic

Context windowcontext_length3

Claim history for Context window
Value	Valid from → to	Status	Source	Confidence	Extractor
262.1K tokens	12 Sept 2026 00:05 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic
256K tokens	11 Sept 2026 22:42 UTC → 12 Sept 2026 00:05 UTC	superseded	Artificial AnalysisT2	medium	deterministic
262.1K tokens	11 Sept 2026 21:10 UTC → 11 Sept 2026 22:42 UTC	superseded	OpenRouter public model & pricing listingT2	medium	deterministic

Max outputmax_output_tokens1

Claim history for Max output
Value	Valid from → to	Status	Source	Confidence	Extractor
65.5K tokens	11 Sept 2026 21:10 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic

Modalitiesmodalities1

Claim history for Modalities
Value	Valid from → to	Status	Source	Confidence	Extractor
text	11 Sept 2026 21:10 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic

Input modalitiesmodalities_input1

Claim history for Input modalities
Value	Valid from → to	Status	Source	Confidence	Extractor
text	11 Sept 2026 21:10 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic

Output modalitiesmodalities_output1

Claim history for Output modalities
Value	Valid from → to	Status	Source	Confidence	Extractor
text	11 Sept 2026 21:10 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic

Hugging Face repohf_repo1

Claim history for Hugging Face repo
Value	Valid from → to	Status	Source	Confidence	Extractor
stepfun-ai/Step-3.5-Flash	11 Sept 2026 21:10 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic

Descriptiondescription1

Claim history for Description
Value	Valid from → to	Status	Source	Confidence	Extractor
Step 3.5 Flash is StepFun's most capable open-source foundation model. Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parameters per token....	11 Sept 2026 21:10 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic

Aa median output tokens per secondmetric.aa_median_output_tokens_per_second1

Claim history for Aa median output tokens per second
Value	Valid from → to	Status	Source	Confidence	Extractor
205.1	11 Sept 2026 22:42 UTC → current	current	Artificial AnalysisT2	medium	deterministic

Openrouter idopenrouter_id1

Claim history for Openrouter id
Value	Valid from → to	Status	Source	Confidence	Extractor
stepfun/step-3.5-flash	11 Sept 2026 21:10 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic

Reasoningreasoning1

Claim history for Reasoning
Value	Valid from → to	Status	Source	Confidence	Extractor
Yes	11 Sept 2026 21:10 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic

Structured outputstructured_output1

Claim history for Structured output
Value	Valid from → to	Status	Source	Confidence	Extractor
No	11 Sept 2026 21:10 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic

Supported parameterssupported_parameters1

Claim history for Supported parameters
Value	Valid from → to	Status	Source	Confidence	Extractor
frequency_penalty, include_reasoning, max_tokens, reasoning, temperature, tool_choice, tools, top_k, top_p	11 Sept 2026 21:10 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic

Tool callingtool_calling1

Claim history for Tool calling
Value	Valid from → to	Status	Source	Confidence	Extractor
Yes	11 Sept 2026 21:10 UTC → current	current	OpenRouter public model & pricing listingT2	medium	deterministic

Claims are temporal and append-only: a new observation closes the previous claim (valid_to) instead of overwriting it. Conflicting claims from different sources are kept side by side and flagged — never averaged. Methodology →

Provenance

Attributed facts

17

Source tiers

T217

Freshest observation

6 h ago

Conflicts

None

Source documents 4

Source documents
Source	Document	Type	Tier	Last observed	Snapshots
OpenRouter public model & pricing listing	openrouter.ai/api/v1/models	catalogue	T2· Quality secondary	6 h ago	5
Hugging Face Hub (public pages, model cards, papers)	huggingface.co/cerebras/Step-3.5-Flash-REAP-149B-A11B	model_page	T2· Quality secondary	7 h ago	5
Hugging Face Hub (public pages, model cards, papers)	huggingface.co/cerebras/Step-3.5-Flash-REAP-121B-A11B	model_page	T2· Quality secondary	7 h ago	5
Artificial Analysis	artificialanalysis.ai/leaderboards/models	leaderboard	T2· Quality secondary	11 h ago	1

Tier 1 = official/primary, 2 = quality secondary, 3 = community, 4 = unverified. Every snapshot is archived; see all sources and the methodology.

Data quality (56/100) measures how well AI Atlas knows this entity — completeness, primary-source ratio, freshness, conflicts — never how good the model is. Methodology →