Specification

Release date: 29 Jan 2026
Source:OpenRouter public model & pricing listingT2observed 3 h agomedium
Status: deprecated
Source:Artificial AnalysisT2observed 2 h agomedium
Openness: open-weights
Source:Artificial AnalysisT2observed 2 h agomedium
Context window: 256K tokens
Source:Artificial AnalysisT2observed 2 h agomedium
Max output: 65.5K tokens
Source:OpenRouter public model & pricing listingT2observed 3 h agomedium
Modalities: text
Source:OpenRouter public model & pricing listingT2observed 3 h agomedium
Input modalities: text
Source:OpenRouter public model & pricing listingT2observed 3 h agomedium
Output modalities: text
Source:OpenRouter public model & pricing listingT2observed 3 h agomedium
Hugging Face repo: stepfun-ai/Step-3.5-Flash
Source:OpenRouter public model & pricing listingT2observed 3 h agomedium
Aa median output tokens per second: 205.1
Source:Artificial AnalysisT2observed 2 h agomedium
Openrouter id: stepfun/step-3.5-flash
Source:OpenRouter public model & pricing listingT2observed 3 h agomedium
Supported parameters: frequency_penalty, include_reasoning, max_tokens, reasoning, temperature, tool_choice, tools, top_k, top_p
Source:OpenRouter public model & pricing listingT2observed 3 h agomedium

Each value shows its source, tier and observation time. Conflicting claims are kept side by side and flagged — never averaged. How AI Atlas records facts →

Provenance

Attributed facts

16

Source tiers

T216

Freshest observation

2 h ago

Conflicts

None

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: 256K tokens
Source:Artificial AnalysisT2observed 2 h agomedium
Max output: 65.5K tokens
Source:OpenRouter public model & pricing listingT2observed 3 h agomedium

Benchmark results
Benchmark	Score	Metric	Config	Evaluated	Source
τ²-bench	94.44%	pass^1	aa_slug=step-3-5-flash-0202 · evaluator=Artificial Analysis · index_version=4.3	—	artificialanalysis.aiT2
Artificial Analysis Intelligence Index	16.62	index	aa_slug=step-3-5-flash-0202 · version=4.3 · estimated=true	—	artificialanalysis.aiT2
GPQA	83.13%	accuracy	aa_slug=step-3-5-flash-0202 · variant=GPQA Diamond · evaluator=Artificial Analysis · index_version=4.3	—	artificialanalysis.aiT2
Humanity's Last Exam	21.13%	accuracy	aa_slug=step-3-5-flash-0202 · evaluator=Artificial Analysis · index_version=4.3	—	artificialanalysis.aiT2
IFBench	64.56%	accuracy	aa_slug=step-3-5-flash-0202 · evaluator=Artificial Analysis · index_version=4.3	—	artificialanalysis.aiT2
Terminal-Bench	27.27%	accuracy	aa_slug=step-3-5-flash-0202 · variant=hard · evaluator=Artificial Analysis · index_version=4.3	—	artificialanalysis.aiT2

Scores are reported as published, with their evaluation configuration (harness, prompting, judge). Results with different configs are not directly comparable — see methodology.

Current prices

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	2 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.

Available through 1

OpenRouter

Price history

Input price · USD / 1M tokens

Output price · USD / 1M tokens

OpenRouter

No hardware estimate available

Estimates need a parameter count; this model has none recorded from a source.

Ancestors 0

None recorded.

This model

Step 3.5 Flash

Quantizations 0

None recorded.

Descendants 2

Step-3.5-Flash-REAP-121B-A11B121B
Step-3.5-Flash-REAP-149B-A11B149.4B

Papers 0

No papers linked yet.

Repositories 0

No repositories linked yet.

As of

Rewind the record: see this entity's attributes exactly as AI Atlas knew them on a given day.

Claim history

13 claims · 13 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

Context windowcontext_length1

Claim history for Context window
Value	Valid from → to	Status	Source	Confidence	Extractor
262.1K tokens	11 Sept 2026 21:10 UTC → current	current	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

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 →

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

Full timeline →

Source documents
Source	Document	Type	Tier	Last observed	Snapshots
Artificial Analysis	artificialanalysis.ai/leaderboards/models	leaderboard	T2· Quality secondary	2 h ago	1
OpenRouter public model & pricing listing	openrouter.ai/api/v1/models	catalogue	T2· Quality secondary	2 h ago	2
Hugging Face Hub (public pages, model cards, papers)	huggingface.co/cerebras/Step-3.5-Flash-REAP-149B-A11B	model_page	T2· Quality secondary	3 h ago	2
Hugging Face Hub (public pages, model cards, papers)	huggingface.co/cerebras/Step-3.5-Flash-REAP-121B-A11B	model_page	T2· Quality secondary	3 h ago	2

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