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gpt-oss-120b vs Step 3.5 Flash

Step 3.5 Flash leads gpt-oss-120b on the Artificial Analysis Intelligence Index, 17.0 to 11.6, and Step 3.5 Flash costs 1.7x less per output token ($0.30 vs $0.50 per million). Updated October 21, 2026; 35 benchmarks have a result for both.

Replace gpt-oss-120b Replace Step 3.5 Flash
gpt-oss-120bOpenAI
Coding
No data
Overall
11.6
Output $/M
$0.50
1
Step 3.5 FlashStepFun
Coding
No data
Overall
17.0
Output $/M
$0.30
34
vs boards won of 35 shared

gpt-oss-120b or Step 3.5 Flash: which to pick

Neither model has a coding score yet, so the two cannot be ranked on coding.

Pick gpt-oss-120b for work measured by Terminal-Bench Hard (Artificial Analysis run) or LMArena Text: coding, where it leads.

Model Agpt-oss-120bOpenAINot benchmarked1 independent benchmark$0.51 per solved taskModel BStep 3.5 FlashStepFunNot benchmarkedNo coding benchmarkNo cost per solved task
Shared results
35
gpt-oss-120b only
43
Step 3.5 Flash only
0
Like-for-like categories
7 of 9

Only benchmarks that tested both models count toward a pick; a result only one model has is shown but not compared.

Which one for your work

Each card is decided by one number both models carry. Where only one has it, the card says so and makes no call.

At a glance

Coding index
gpt-oss-120b not benchmarked, Step 3.5 Flash not benchmarked.
Widest category
Agentic work, 28.7 points apart on average over 1 shared benchmark.
Widest single gap
τ²-Bench Telecom: gpt-oss-120b 65.8% against Step 3.5 Flash 94.4%, 28.7 points apart on a 0 to 100 scale.
Output price
gpt-oss-120b $0.50 against Step 3.5 Flash $0.30 per million output tokens, 1.7x apart.
Context window
gpt-oss-120b takes 131K tokens, Step 3.5 Flash 262K.

Benchmark by benchmark

First the score: boards each model leads, per category, where both have a result. Then every board, a category to a fold; bars are each result on a 0 to 100 scale, so compare the two in a row, not one row with another.

Boards won, where both have a result
Categorygpt-oss-120bBarsStep 3.5 FlashTies
Coding03
Intelligence01
Agentic work01
Reasoning05
Math02
Knowledge04
General118
All shared boards134
CodingLike-for-likeSix of these boards feed the Vibe Coding Index03
Coding benchmarks for gpt-oss-120b and Step 3.5 Flash
Benchmarkgpt-oss-120bStep 3.5 FlashLeader
Aider polyglot41.8%Not measuredOnly gpt-oss-120b measured
SWE-bench Verified26.0%Not measuredOnly gpt-oss-120b measured
AA Coding Index30.4Not measuredOnly gpt-oss-120b measured
LiveCodeBench (Vals AI)83.2%Not measuredOnly gpt-oss-120b measured
SWE-bench Verified (Vals AI)33.6%Not measuredOnly gpt-oss-120b measured
LiveCodeBench (Artificial Analysis run)87.8%Not measuredOnly gpt-oss-120b measured
SciCode34.0%Not measuredOnly gpt-oss-120b measured
Terminal-Bench Hard (Artificial Analysis run)23.5%32.6%Step 3.5 Flash
Terminal-Bench18.7%Not measuredOnly gpt-oss-120b measured
WeirdML48.2%Not measuredOnly gpt-oss-120b measured
ALE-Bench575.6Not measuredOnly gpt-oss-120b measured
LMArena Text: coding13791436Step 3.5 Flash
LMArena Text: software and IT13871434Step 3.5 Flash
Neither model has a result on the other 25 boards here
IntelligenceLike-for-likePublic boards, shown as published, kept out of the index01
Intelligence benchmarks for gpt-oss-120b and Step 3.5 Flash
Benchmarkgpt-oss-120bStep 3.5 FlashLeader
AA Intelligence Index11.617.0Step 3.5 Flash
Epoch Capabilities Index139.8Not measuredOnly gpt-oss-120b measured
Agentic workLike-for-likePublic boards, shown as published, kept out of the index01
Agentic work benchmarks for gpt-oss-120b and Step 3.5 Flash
Benchmarkgpt-oss-120bStep 3.5 FlashLeader
AA Agentic Index3.7Not measuredOnly gpt-oss-120b measured
τ²-Bench Telecom65.8%94.4%Step 3.5 Flash
APEX-Agents4.4%Not measuredOnly gpt-oss-120b measured
METR time horizons56.6%Not measuredOnly gpt-oss-120b measured
Vending-Bench 2-$22Not measuredOnly gpt-oss-120b measured
Neither model has a result on the other 34 boards here
ReasoningLike-for-likePublic boards, shown as published, kept out of the index05
Reasoning benchmarks for gpt-oss-120b and Step 3.5 Flash
Benchmarkgpt-oss-120bStep 3.5 FlashLeader
GPQA Diamond78.5%Not measuredOnly gpt-oss-120b measured
GPQA Diamond (Artificial Analysis run)78.2%83.1%Step 3.5 Flash
Humanity's Last Exam (Artificial Analysis run)19.6%24.5%Step 3.5 Flash
GPQA Diamond (Epoch AI run)75.8%Not measuredOnly gpt-oss-120b measured
SimpleBench22.1%Not measuredOnly gpt-oss-120b measured
Mystery game puzzles2.0%Not measuredOnly gpt-oss-120b measured
LMArena Text: hard prompts13641411Step 3.5 Flash
LMArena Text: expert13561421Step 3.5 Flash
LMArena Text: hard prompts in English13681421Step 3.5 Flash
Neither model has a result on the other 12 boards here
MathLike-for-likePublic boards, shown as published, kept out of the index02
Math benchmarks for gpt-oss-120b and Step 3.5 Flash
Benchmarkgpt-oss-120bStep 3.5 FlashLeader
AIME92.6%Not measuredOnly gpt-oss-120b measured
MATH 500 (Vals AI)94.8%Not measuredOnly gpt-oss-120b measured
MGSM (Vals AI)92.0%Not measuredOnly gpt-oss-120b measured
AA Math Index93.4Not measuredOnly gpt-oss-120b measured
AIME 2025 (Artificial Analysis run)93.4%Not measuredOnly gpt-oss-120b measured
OTIS Mock AIME88.9%Not measuredOnly gpt-oss-120b measured
LMArena Text: math13891408Step 3.5 Flash
LMArena Text: mathematical work13861421Step 3.5 Flash
Neither model has a result on the other 5 boards here
KnowledgeLike-for-likePublic boards, shown as published, kept out of the index04
Knowledge benchmarks for gpt-oss-120b and Step 3.5 Flash
Benchmarkgpt-oss-120bStep 3.5 FlashLeader
MMLU Pro79.2%Not measuredOnly gpt-oss-120b measured
LegalBench (Vals AI)75.9%Not measuredOnly gpt-oss-120b measured
CaseLaw (Vals AI)48.8%Not measuredOnly gpt-oss-120b measured
CorpFin (Vals AI)58.2%Not measuredOnly gpt-oss-120b measured
TaxEval (Vals AI)71.6%Not measuredOnly gpt-oss-120b measured
MedQA (Vals AI)91.4%Not measuredOnly gpt-oss-120b measured
MMLU Pro (Artificial Analysis run)80.8%Not measuredOnly gpt-oss-120b measured
LMArena Text: science13821415Step 3.5 Flash
LMArena Text: medicine and healthcare13881408Step 3.5 Flash
LMArena Text: legal and government13551408Step 3.5 Flash
LMArena Text: business and finance13591394Step 3.5 Flash
Neither model has a result on the other 6 boards here
Web designDirectional onlyPublic boards, shown as published, kept out of the index6 boards, none shared
Web design benchmarks for gpt-oss-120b and Step 3.5 Flash
Benchmarkgpt-oss-120bStep 3.5 FlashLeader
Design Arena: websites968Not measuredOnly gpt-oss-120b measured
Design Arena: UI components927Not measuredOnly gpt-oss-120b measured
Design Arena: game dev992Not measuredOnly gpt-oss-120b measured
Design Arena: data viz987Not measuredOnly gpt-oss-120b measured
Design Arena: 3D901Not measuredOnly gpt-oss-120b measured
Design Arena: all code categories963Not measuredOnly gpt-oss-120b measured
Neither model has a result on the other 3 boards here
GeneralLike-for-likePublic boards, shown as published, kept out of the index118
General benchmarks for gpt-oss-120b and Step 3.5 Flash
Benchmarkgpt-oss-120bStep 3.5 FlashLeader
IFBench69.0%66.5%gpt-oss-120b
Long context reasoning (AA-LCR)52.0%63.0%Step 3.5 Flash
DTBench76.3%Not measuredOnly gpt-oss-120b measured
LMCA22.1%Not measuredOnly gpt-oss-120b measured
Fiction.LiveBench44.4%Not measuredOnly gpt-oss-120b measured
Creative writing (Lech Mazur)77.1%Not measuredOnly gpt-oss-120b measured
Surface Evolver Bench25.0%Not measuredOnly gpt-oss-120b measured
LMArena Text13661403Step 3.5 Flash
LMArena Text: instruction following13181385Step 3.5 Flash
LMArena Text: creative writing12741357Step 3.5 Flash
LMArena Text: English13751417Step 3.5 Flash
LMArena Text: non-English13511385Step 3.5 Flash
LMArena Text: Chinese13851446Step 3.5 Flash
LMArena Text: German13531405Step 3.5 Flash
LMArena Text: Japanese13311353Step 3.5 Flash
LMArena Text: Korean12821351Step 3.5 Flash
LMArena Text: French13701421Step 3.5 Flash
LMArena Text: Spanish13891419Step 3.5 Flash
LMArena Text: Russian13431385Step 3.5 Flash
LMArena Text: Polish13531389Step 3.5 Flash
LMArena Text: multi-turn13401404Step 3.5 Flash
LMArena Text: longer queries13191402Step 3.5 Flash
LMArena Text: writing and language13061372Step 3.5 Flash
LMArena Text: entertainment and media12921360Step 3.5 Flash
Neither model has a result on the other 22 boards here
Image generationNot comparablePublic boards, shown as published, kept out of the index0 boards, none shared
Image generation benchmarks for gpt-oss-120b and Step 3.5 Flash
Benchmarkgpt-oss-120bStep 3.5 FlashLeader
Neither model has a result on 5 boards here

What each workload costs

Three fixed token mixes at each model's listed price, so per-token rates become a bill.

Chat turn

1K input + 500 output tokens

gpt-oss-120b$0.0003Fits in one request
Step 3.5 Flash$0.0003Fits in one request

Step 3.5 Flash costs less

Repository review

50K input + 3K output tokens

gpt-oss-120b$0.0065Fits in one request
Step 3.5 Flash$0.0059Fits in one request

Step 3.5 Flash costs less

Agent loop

200K input + 10K output tokens

gpt-oss-120b$0.025Exceeds the context window
Step 3.5 Flash$0.023Fits in one request

Step 3.5 Flash costs less

Listed OpenRouter rates, without cache or batch discounts. A workload that does not fit a model's context window would need splitting.

Specification differences

The leading value in a row is marked; a row with a missing value names no leader. Our two rows are marked in red.

Specifications of gpt-oss-120b and Step 3.5 Flash
SpecificationOpenAI gpt-oss-120bStepFun Step 3.5 Flash
MakerOpenAIStepFun
WeightsOpen weightsOpen weights
ReleasedAugust 5, 2025January 29, 2026
Context window131K262K
Input $/Mtok$0.10$0.10
Output $/Mtok$0.50$0.30
Coding indexNot benchmarkedNot benchmarked
Independent measurements behind it10
Cost per solved task$0.51Not computable
SourceOpenRouter listingOpenRouter listing

Questions

Is gpt-oss-120b better than Step 3.5 Flash for coding?

Neither model has a coding score yet, so the two cannot be ranked on coding. Pick gpt-oss-120b for work measured by Terminal-Bench Hard (Artificial Analysis run) or LMArena Text: coding, where it leads.

Which is cheaper, gpt-oss-120b or Step 3.5 Flash?

gpt-oss-120b costs $0.10 per million input tokens and $0.50 per million output tokens; Step 3.5 Flash costs $0.10 and $0.30. Cost per solved task is known for gpt-oss-120b only.

Which has the bigger context window, gpt-oss-120b or Step 3.5 Flash?

Step 3.5 Flash, with 262K tokens against 131K.

How many benchmarks is the gpt-oss-120b vs Step 3.5 Flash comparison based on?

35 benchmarks have a result for both models as of October 21, 2026. gpt-oss-120b's coding index rests on 1 independent benchmark and Step 3.5 Flash's on 0. Where only one model has a result, the page says so instead of naming a winner.

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