Models › Step-3.5 family

stepfun-ai Apache 2.0 out 9 months ago

199B parameters (8 of 288 experts per token), text in, text out, 256K tokens of context. 2 providers serve it from $0.10 per million input tokens.

Verified 2026-10-25 Rank #111 in LLMs · score 98.1 method v1 Sources 4 Downloads 30d 265.3k · #226 of 619 tracked

What does it cost?$0.10/1M incheapest of 1SiliconFlowfp82026-10-24
Can I use it?Apache 2.0Permissive; patent grantlicence file2026-10-24
Do people use it?265.3kdownloads, 30 days#226 of 619 we track · top 37%+4 likes, downloads +1% this week844 likesHugging Face2026-10-24

Worth reading

Picked by rule from 12 tracked pieces: the lab's own post, the most shared, a field report, the latest.

Step 3.5 Flash synthesizes a comprehensive research report of approximately 10,000 words on early childhood science education.

From Step 3.5 Flash – Open-source foundation model, supports deep reasoning at speed · static.stepfun.com · 2026-02-02
The lab's own post

Step 3.5 Flash – Open-source foundation model, supports deep reasoning at speed

Step 3.5 Flash is a sparse MoE open-source model with 196B total parameters that activates only 11B per token.

  • The model is compatible with Claude Code, serving as an efficient backend for agent-led development.
  • Step 3.5 Flash synthesizes a comprehensive research report of approximately 10,000 words on early childhood science education.
static.stepfun.com 2026-02-02 231 HN pts · 91 comments 3.1k words

12 best of 12 tracked

The 5 picks above, plus these 7. Top is the radar's score: discussion, source authority and the lab's own posts, fading with age.

  1. PaperStep 3.5 Flash: Open Frontier-Level Intelligence with 11B Active Parametersarxiv.org · undated
  2. CodeStep-3.5-Flash Technical Report [pdf]github.com · 2026-02-05 · 1 HN pts
  3. ArticleStep 3.5 Flash Now on SiliconFlow: Deep Thinking at ...siliconflow.com · undated
  4. Articlestepfun-ai / step-3.5-flashdocs.api.nvidia.com · undated
  5. ArticleStep 3.5 Flash Review 2026: Better Than GPT-5? (We Tested It)computertech.co · 2026-02-19
  6. ArticleStep 3.5 Flash: Open Frontier-Level Intelligence with 11B Active Parameters [Quick Review]liner.com · 2026-02-11
  7. ArticleStep 3.5 Flashi-scoop.eu · 2026-02-04

Where to run it

Live hosted endpoints, cheapest first, USD per million tokens. Ties break on output price, then provider name.

#Cheapest 2In /1MOut /1MContextQuantSeen
1 SiliconFlow $0.10 $0.30 256K fp8 Oct 24
2 Featherless — — — — Oct 25

All 2 providers →

Where it's used

Hugging Face does not say who downloads a model or with what. These are the proxies: API providers listing it, quantized builds, fine-tunes/adapters/merges, and Spaces that load it.

Served by 2 API providers; 23 quantized builds for local use.

  • As a service2Featherless, SiliconFlow
  • On own hardware23quantized builds
  • Built on77 fine-tunes · 0 adapters · 0 merges
  • In apps99Hugging Face Spaces

Top Spaces running it: hadadxyz/ai ♥ 819 · pliny-the-prompter/obliteratus ♥ 621 · stepfun-ai/Step-3.5-Flash ♥ 50 · Kodacoda/obliteratus ♥ 2

Will it fit?

Weights only, an estimate: leave room for the KV cache. Method

Fits two 80 GB GPUs at INT4; too big for one

About 120 GB at INT4, 239 GB at FP8, 479 GB at BF16: weights only, so leave room for the KV cache. Every expert must be resident, so total parameters count.

16 GB card64 GB Mac2×80 GB8×80 GBINT4: about 120 GB of weights (estimate; KV cache and activations extra)INT4120 GBFP8: about 239 GB of weights (estimate; KV cache and activations extra)FP8239 GBBF16: about 479 GB of weights (estimate; KV cache and activations extra)BF16479 GB
16 GB card64 GB Mac2×80 GB8×80 GBINT4: about 120 GB of weights (estimate; KV cache and activations extra)INT4120 GBFP8: about 239 GB of weights (estimate; KV cache and activations extra)FP8239 GBBF16: about 479 GB of weights (estimate; KV cache and activations extra)BF16479 GB

Estimate params × bytes per param × 1.2 · how we estimate

The story so far

Weights, every dated article, and repo commits on one rail.

Most coverage came in the first two weeks

Teal is the weights (2026-02-01), amber triangles are 5 dated articles (each links to it), grey ticks are repo commits.

MarAprMayJunJulAugSepOct2026-03-17: 1 repo commit2026-03-09: 1 repo commit2026-02-13: 1 repo commit2026-02-12: 3 repo commits2026-02-07: 1 repo commit2026-02-06: 4 repo commits2026-02-05: 1 repo commit2026-02-03: 2 repo commits2026-02-02: 13 repo commits2026-02-01: 3 repo commitsStep 3.5 Flash – Open-source foundation model, supports deep reasoning at speed · 2026-02-02Step 3.5 Flash: Open Frontier-Level Intelligence with 11B Active Parameters · 2026-02-12Step-3.5-Flash Technical Report [pdf] · 2026-02-05A new local LLM king: Step-3.5-Flash-int4 · 2026-02-02Step 3.5 Flash Review 2026: Better Than GPT-5? (We Tested It) · 2026-02-19Weights 2026-02-01 · 2026-02-01Weights 2026-02-01now · 2 providers
MarAprMayJunJulAugSepOct2026-03-17: 1 repo commit2026-03-09: 1 repo commit2026-02-13: 1 repo commit2026-02-12: 3 repo commits2026-02-07: 1 repo commit2026-02-06: 4 repo commits2026-02-05: 1 repo commit2026-02-03: 2 repo commits2026-02-02: 13 repo commits2026-02-01: 3 repo commitsStep 3.5 Flash – Open-source foundation model, supports deep reasoning at speed · 2026-02-02Step 3.5 Flash: Open Frontier-Level Intelligence with 11B Active Parameters · 2026-02-12Step-3.5-Flash Technical Report [pdf] · 2026-02-05A new local LLM king: Step-3.5-Flash-int4 · 2026-02-02Step 3.5 Flash Review 2026: Better Than GPT-5? (We Tested It) · 2026-02-19Weights 2026-02-01 · 2026-02-01Weights 2026-02-01now · 2 providers

What people built on it

30 derivatives on the Hub. Which build to run, by runtime: the most downloaded in each class.

30 derivatives on the Hub, most of them quantized

From the Hugging Face model tree; quantized builds in teal, fine-tunes, merges and adapters in greys.

23 quantized (Hugging Face model tree)7 fine-tunes (Hugging Face model tree)23 quantized7 fine-tunes
23 quantized (Hugging Face model tree)7 fine-tunes (Hugging Face model tree)23 quantized7 fine-tunes

All variants →

Reference

Everything else, folded: the full tables, every source.

Benchmarks

21 rows

Benchmarks 21 rows

measured third-party leaderboard rowauthor-reported number from the model card or eval files (21)No confidence intervals unless the source gave them; settings differ between rows, so compare within a benchmark, not across. Date = the benchmark's own date when it gives one, else when we read it.
BenchmarkValueSetting / notesReported byDate
author-reported AIME 2025 · Reason through hard problems97.3—model author2026-10-07
author-reported BrowseComp51.6—model author2026-10-07
author-reported BrowseComp (w/ Context Manager)69—model author2026-10-07
author-reported BrowseComp-ZH66.9—model author2026-10-07
author-reported BrowseComp-ZH (w/ Context Manager)73.7—model author2026-10-07
author-reported GAIA (no file)84.5—model author2026-10-07
author-reported HMMT · Reason through hard problems98.4—model author2026-10-07
author-reported HMMT · Reason through hard problems94—model author2026-10-07
author-reported IMO-AnswerBench · Reason through hard problems85.4—model author2026-10-07
author-reported LiveCodeBench · Write code with agents86.4—model author2026-10-07
author-reported ResearchRubrics65.3—model author2026-10-07
author-reported SWE-bench Verified · Write code with agents74.4—model author2026-10-07
author-reported Terminal-Bench · Write code with agents51—model author2026-10-07
author-reported xbench-DeepSearch (2025.05)83.7—model author2026-10-07
author-reported xbench-DeepSearch (2025.10)56.3—model author2026-10-07
author-reported τ²-Bench88.2—model author2026-10-07
author-reported diamond (Idavidrein/gpqa)83.5—Step 3.5 Flash Paper2026-02-11
author-reported hle (cais/hle)23.1Text OnlyStep 3.5 Flash Paper2026-02-11
author-reported mmlu_pro (TIGER-Lab/MMLU-Pro)84.4—Step 3.5 Flash Paper2026-02-11
author-reported swe_bench_%_resolved (SWE-bench/SWE-bench_Verified)74.4—Step 3.5 Flash Paper2026-02-11
author-reported terminalbench_2 (harborframework/terminal-bench-2.0)51—Step 3.5 Flash Paper2026-02-11

What the card says

1 cited sentence

Summary generated, cited

The model uses a sparse Mixture of Experts architecture and supports a 256K context window.[1][2]

  1. “Built on a sparse Mixture of Experts (MoE) architecture”
  2. “256K context window”

Generated 2026-10-07 15:01 UTC by parasail-gemma-4-26b-a4b-it; each numeral points at the fact it rests on. Not a verdict.

Use-case evidence

5 use cases

What it is good at 5 use cases

Labels are evidence, not verdicts: measured a third-party leaderboard row for this model; author-reported a number the model author published in the card or eval files; structural a deterministic signal from the name, config or chat template, or a decision-model estimate. Each chip links to its source. All use cases.

Facts

22 fields

Listed in LLMs

Facts

Pipeline tagtext-generation
Librarytransformers
ArchitecturesStep3p5ForCausalLM
Model typestep3p5
Dtypebfloat16
Params by dtypeBF16: 199,384,289,280 · F32: 12,096
Size bandXXL
MoEyes
Experts288
Experts per token8
Context length262,144 (config.json max_position_embeddings)
PapersarXiv:2602.10604, arXiv:2601.05593, arXiv:2507.19427
LicenseApache 2.0 (apache-2.0)
Hub snapshot2026-10-25

Servability

vLLM · SGLang

Servability

vLLM: supported · Step3p5ForCausalLM · 7050ef881ff0835f6890a47db1859a24c65481d6SGLang: supported · Step3p5ForCausalLM · 773cb938fe9484a8f7e7e46fb1b1fe96412c59ed

vLLM registry (7050ef881ff0835f6890a47db1859a24c65481d6) · SGLang registry (773cb938fe9484a8f7e7e46fb1b1fe96412c59ed) · Matched by architecture class name against each project's registry on main; 'supported' means the architecture is registered, not that this checkpoint was tested.

Hardware fit

3 estimates

Hardware fit ESTIMATE

Weights-only memory for Step-3.5-Flash: params × bytes/param × 1.2 overhead. KV cache and activations are extra. How this is computed.

BF16 (2 bytes/param)479 GB · Multi-GPU node (<640 GB)
FP8 (1 byte/param)239 GB · Multi-GPU node (<640 GB)
INT4 (0.5 bytes/param)120 GB · Multi-GPU node (<640 GB)

Weights only (params × bytes/param × 1.2 overhead); KV cache and activations extra. MoE: all experts must be resident, so total parameters count.

All variants

30 variants

Lineage

Original model Family: stepfun-ai/Step-3.5 30 derivatives on the Hub

quantized: 23finetune: 7

Top variants (30 shown, ranked by downloads)

Relation
Quant
Size
30 rows
Variant Relation Quant Params Band License Author Likes Downloads
bartowski/stepfun-ai_Step-3.5-Flash-GGUF quantized GGUF — — apache-2.0 bartowski 43 46.9k
ggml-org/Step-3.5-Flash-GGUF quantized GGUF — — — ggml-org 15 44.9k
mradermacher/Step-3.5-Flash-i1-GGUF quantized GGUF — — apache-2.0 mradermacher 1 28k
QuantPasture/Step-3.5-Flash-GGUF quantized GGUF — — — QuantPasture 20 23.1k
mudler/Step-3.5-Flash-APEX-GGUF quantized GGUF — — other mudler 7 15.7k
mlx-community/Step-3.5-Flash-4bit quantized -4bit 197B XXL apache-2.0 mlx-community 10 14.5k
ubergarm/Step-3.5-Flash-GGUF quantized GGUF — — apache-2.0 ubergarm 44 12.2k
Ex0bit/Step-3.5-Flash-PRISM finetune GGUF — — other Ex0bit 19 7.5k
mlx-community/Step-3.5-Flash-8bit quantized -8bit 197B XXL apache-2.0 mlx-community 2 5.4k
tacos4me/Step-3.5-Flash-NVFP4 quantized NVFP4 111B XXL apache-2.0 tacos4me 10 4.9k
mlx-community/Step-3.5-Flash-6bit quantized — 197B XXL apache-2.0 mlx-community 1 3.5k
Intel/Step-3.5-Flash-int4-mixed-AutoRound quantized int4 44.0B XL apache-2.0 Intel 9 3k
noctrex/Step-3.5-Flash-MXFP4_MOE-GGUF quantized GGUF — — — noctrex 2 2.9k
mradermacher/Step-3.5-Flash-GGUF quantized GGUF — — apache-2.0 mradermacher 2 2.5k
cerebras/Step-3.5-Flash-REAP-121B-A11B finetune — 121B XXL other cerebras 15 1.2k
Kilinskiy/Step-3.5-Flash-Ablitirated finetune — 197B XXL apache-2.0 Kilinskiy 8 994
mlx-community/Step-3.5-Flash-bf16 finetune -bf16 197B XXL apache-2.0 mlx-community 1 1.1k
tnhnyzc/Step-3.5-Flash-MTP-GGUF quantized GGUF — — apache-2.0 tnhnyzc 1 1.1k
Firworks/Step-3.5-Flash-nvfp4 quantized nvfp4 111B XXL — Firworks 0 1.1k
amd/Step-3.5-Flash-MXFP4 quantized MXFP4 102B XXL apache-2.0 amd 2 905
DevQuasar/stepfun-ai.Step-3.5-Flash-GGUF quantized GGUF — — — DevQuasar 0 1k
lkevincc0/Step-3.5-Flash-REAP-128B-A11B quantized — 121B XXL apache-2.0 lkevincc0 10 498
cerebras/Step-3.5-Flash-REAP-149B-A11B finetune — 149B XXL other cerebras 5 608
m-i/Step-3.5-Flash-mixed-2-8bit quantized -8bit 197B XXL apache-2.0 m-i 0 753
terribleplan/stepfun-ai_Step-3.5-Flash quantized GGUF — — — terribleplan 1 694
mixer3d/step-3.5-flash-imatrix-gguf quantized imatrix — — apache-2.0 mixer3d 2 633
ramgpt/Step-3.5-Flash-GGUF-Q4_K_M quantized GGUF — — other ramgpt 1 400
turboderp/Step-3.5-Flash-exl3 quantized exl3 — — apache-2.0 turboderp 5 94
Ex0bit/Step-3.5-Flash-PRISM-PRO finetune — 197B XXL other Ex0bit 4 34
quan3s/Llmofhacker finetune — — — apache-2.0 quan3s 0 0

Repository changelog

30 commits

Repository changelog 30 commits

DateCommitSHA
2026-03-17 Add evaluation results from Step 3.5 Flash paper ab446a3
2026-03-09 Update config.json ef9cf3c
2026-02-13 Update README.md a612345
2026-02-12 Update README.md c7f7136
2026-02-12 Update README.md ade370d
2026-02-12 Update README.md 358677d
2026-02-07 Update README.md a9197e1
2026-02-06 Upload step-bar-chart.png (#20) ec9ad06
2026-02-06 update bmk numbers (#19) 5bf071c
2026-02-06 Update README.md 50aa037
2026-02-06 Update README.md 14cd490
2026-02-05 Update README.md 06ab720
2026-02-03 Adding `transformers` as the library name. (#7) 2f9234a
2026-02-03 Update config.json (#9) 7eb38d5
2026-02-02 Delete generation_config.json 415bdfc
2026-02-02 Update README.md 4eaed1c
2026-02-02 Update README.md aaa7e7d
2026-02-02 Create generation_config.json b216970
2026-02-02 Update config.json (#4) e2554be
2026-02-02 Update README.md 16e32f3
2026-02-02 Update README.md 8847e96
2026-02-02 Update Step-3.5-Flash vLLM recipe (#1) 6c124fa
2026-02-02 Update README.md 6ec21e7
2026-02-02 Update README.md efffd8d
2026-02-02 Update README.md 5462fc4
2026-02-02 Update README.md e8565d1
2026-02-02 Update README.md 43df2bb
2026-02-01 Update README.md 710ac08
2026-02-01 upload step3p5_flash_release_mtp3_bf16 8fb8cbc
2026-02-01 Update README.md 3eb118b

All providers

2 providers · 2 endpoints

Where to run 2 providers · 2 endpoints

Hosted endpoints observed for Step-3.5-Flash, sorted by input price (USD per million tokens). Each row names its observer and date; prices change daily, so check the source before quoting. Cheapest observed input price: $0.10/M.

ProviderModel refContextQuant$/M in$/M outtok/sTTFTToolsStatusObserved
SiliconFlow
openrouter
stepfun/step-3.5-flash 256K fp8 $0.10 $0.30 — — yes live 2026-10-24
Featherless
hf
stepfun-ai/Step-3.5-Flash — — — — — — — live 2026-10-25

Articles and coverage

12 pieces

Ranked by source signals (HN, Lobsters, authority domains, official posts) and recency. Summaries are generated from a stored copy of the article text; every sentence cites a span of that text, and nothing is shown that failed the citation check.

Official1

static.stepfun.com2026-02-02officialHN front pageHN 231 pts · 91 comments3,135 words
Step 3.5 Flash is a sparse MoE open-source model with 196B total parameters that activates only 11B per token. It achieves 100–300 tok/s throughput using MTP-3 and scores 74.4% on SWE-bench Verified. The model supports a 256K context window via a 3:1 Sliding Window Attention ratio and runs securely on high-end consumer hardware like Mac Studio M4 Max. It distinguishes itself through a unique "Think-and-Act" synergy in tool environments.written, reviewed, cited
  • The model is compatible with Claude Code, serving as an efficient backend for agent-led development.
  • Step 3.5 Flash synthesizes a comprehensive research report of approximately 10,000 words on early childhood science education.
  • The model achieves a score of 65.27% on the Scale AI Research Rubrics benchmark for deep research tasks.

Analysis8

arxiv.orgauthority24,483 words
Step 3.5 Flash is a sparse Mixture-of-Experts model with 196B total parameters and 11B active parameters designed for efficient agentic inference. It achieves 85.4% on IMO-AnswerBench and 86.4% on LiveCodeBench-v6 while utilizing Metropolis Independence Sampling-Filtered Policy Optimization (MIS-PO) for stable reinforcement learning. The architecture scales the context window to 128k and employs interleaved 3:1 Sliding Window/Full Attention to minimize latency during multi-round interactions.written, reviewed, cited
  • Step 3.5 Flash Base scores 31.6% on SimpleQA, surpassing DeepSeek-V3.2-Exp Base despite using only one-third of the parameters.
  • The architecture is constrained to under 200B parameters to enable high-performance inference within the 128GB memory budget of high-end workstations.
arxiv.org2026-02-12authorityHN 1 pts · 1 comments390 words
Step 3.5 Flash is a sparse Mixture-of-Experts model that bridges frontier-level agentic intelligence and computational efficiency. It pairs a 196B-parameter foundation with 11B active parameters and uses interleaved 3:1 sliding-window/full attention with Multi-Token Prediction (MTP-3) to reduce latency. The model achieves 85.4% on IMO-AnswerBench and 86.4% on LiveCodeBench-v6, demonstrating performance comparable to frontier models like GPT-5.2 xHigh.written, reviewed, cited
github.comauthority2,404 words
Step 3.5 Flash is a 196B parameter sparse MoE model that activates only 11B parameters per token using a strategy of selecting Top-8 experts from 288 routed experts per layer. It achieves 100–300 tok/s throughput via 3-way Multi-Token Prediction and scores 74.4% on SWE-bench Verified while supporting a 256K context window with 3:1 Sliding Window Attention. The model is available via OpenRouter free and paid tiers, and the China platform requires +86 phone verification.written, reviewed, cited
  • The model requires a specific patch file to run on vLLM until full MTP3 support is integrated.
  • Deployment on llama.cpp mainline may require building with PR #1867 to resolve tool calling issues.
github.com2026-02-05authorityHN 1 pts · 0 comments
siliconflow.com971 words
docs.api.nvidia.com1,393 words
deepinfra.com1,517 words
computertech.co2026-02-192,744 words

Community1

old.reddit.com2026-02-02HN 2 pts · 1 comments
All coverage tracked for this model (12) — append-only, nothing is ever removed

Papers

3 papers

Papers 3

arXiv links found in the model card and its tags. "Peer-reviewed" is shown only with evidence: a published venue in OpenAlex (measured) or the authors' own journal reference on arXiv (reported).

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Sources

4 sources

Sources

Hub snapshot: 2026-10-25 · HF API: 2026-10-24 21:34 UTC · Providers: 2026-10-24 21:44 UTC · Articles: 2026-10-24 21:45 UTC · Summary: 2026-10-07 15:01 UTC · Last verified 2026-10-25

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