Step 3.5 Flash vs Solar Pro 4
Updated October 21, 2026. 32 benchmarks have a result for both. Coding is ranked on the Vibe Coding Index; every other board is shown as published.
Decision reading
Neither model has a coding score yet, so the two cannot be ranked on coding.
Step 3.5 Flash has the edge where output tokens cost 2.0x less, and where what matters is LMArena Text: coding or AA Intelligence Index, where it leads.
- Shared results
- 32
- Step 3.5 Flash only
- 3
- Solar Pro 4 only
- 13
- Like-for-like categories
- 6 of 9
Shared results can support a head-to-head reading. Results only one model has describe coverage, not superiority.
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.
Coding
Vibe Coding Index, six public coding benchmarks
No call
Neither has a coding score yet.
One side not measured
Intelligence
AA Intelligence Index
Solar Pro 4
Solar Pro 4 leads, 28.2 against 17.0.
Same board, both measured
Web design
Design Arena: websites
No call
Only Solar Pro 4 has a Design Arena: websites result, 1177.
Directional only
Long documents
Listed context window
Solar Pro 4
Solar Pro 4 takes 524K tokens against 262K.
Listed by OpenRouter
Everyday cost
1K input + 500 output tokens
Step 3.5 Flash
Step 3.5 Flash $0.0003, Solar Pro 4 $0.0004 per turn.
List prices
At a glance
- Coding index
- Step 3.5 Flash not benchmarked, Solar Pro 4 not benchmarked.
- Widest category
- Intelligence, 11.2 points apart on average over 1 shared benchmark.
- Widest single gap
- LMArena Text: Polish: Step 3.5 Flash 1389 against Solar Pro 4 1304, 14.1 points apart on a 0 to 100 scale.
- Output price
- Step 3.5 Flash $0.30 against Solar Pro 4 $0.60 per million output tokens, 2.0x apart.
- Context window
- Step 3.5 Flash takes 262K tokens, Solar Pro 4 524K.
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.
| Category | Step 3.5 Flash | Bars | Solar Pro 4 | Ties |
|---|---|---|---|---|
| Coding | 1 | 1 | ||
| Intelligence | 0 | 1 | ||
| Reasoning | 1 | 4 | ||
| Math | 0 | 2 | ||
| Knowledge | 4 | 0 | ||
| General | 16 | 2 | ||
| All shared boards | 22 | 10 |
CodingLike-for-likeSix of these boards feed the Vibe Coding Index11
| Benchmark | Step 3.5 Flash | Solar Pro 4 | Leader |
|---|---|---|---|
| LMArena WebDev | Not measured | 1371 | Only Solar Pro 4 measured |
| AA Coding Index | Not measured | 52.7 | Only Solar Pro 4 measured |
| SciCode | Not measured | 48.0% | Only Solar Pro 4 measured |
| Terminal-Bench Hard (Artificial Analysis run) | 32.6% | Not measured | Only Step 3.5 Flash measured |
| ALE-Bench | Not measured | 179.3 | Only Solar Pro 4 measured |
| LMArena Text: coding | 1436 | 1438 | Solar Pro 4 |
| LMArena Text: software and IT | 1434 | 1431 | Step 3.5 Flash |
| LMArena WebDev: React | Not measured | 1363 | Only Solar Pro 4 measured |
| LMArena WebDev: HTML | Not measured | 1371 | Only Solar Pro 4 measured |
| Neither model has a result on the other 29 boards here | |||
IntelligenceLike-for-likePublic boards, shown as published, kept out of the index01
| Benchmark | Step 3.5 Flash | Solar Pro 4 | Leader |
|---|---|---|---|
| AA Intelligence Index | 17.0 | 28.2 | Solar Pro 4 |
| Neither model has a result on the other 1 board here | |||
Agentic workDirectional onlyPublic boards, shown as published, kept out of the index2 boards, none shared
| Benchmark | Step 3.5 Flash | Solar Pro 4 | Leader |
|---|---|---|---|
| Design Arena: agents building web apps | Not measured | 1105 | Only Solar Pro 4 measured |
| τ²-Bench Telecom | 94.4% | Not measured | Only Step 3.5 Flash measured |
| Neither model has a result on the other 37 boards here | |||
ReasoningLike-for-likePublic boards, shown as published, kept out of the index14
| Benchmark | Step 3.5 Flash | Solar Pro 4 | Leader |
|---|---|---|---|
| GPQA Diamond (Artificial Analysis run) | 83.1% | 89.1% | Solar Pro 4 |
| Humanity's Last Exam (Artificial Analysis run) | 24.5% | 29.8% | Solar Pro 4 |
| LMArena Text: hard prompts | 1411 | 1400 | Step 3.5 Flash |
| LMArena Text: expert | 1421 | 1428 | Solar Pro 4 |
| LMArena Text: hard prompts in English | 1421 | 1427 | Solar Pro 4 |
| Neither model has a result on the other 16 boards here | |||
MathLike-for-likePublic boards, shown as published, kept out of the index02
| Benchmark | Step 3.5 Flash | Solar Pro 4 | Leader |
|---|---|---|---|
| LMArena Text: math | 1408 | 1421 | Solar Pro 4 |
| LMArena Text: mathematical work | 1421 | 1427 | Solar Pro 4 |
| Neither model has a result on the other 11 boards here | |||
KnowledgeLike-for-likePublic boards, shown as published, kept out of the index40
| Benchmark | Step 3.5 Flash | Solar Pro 4 | Leader |
|---|---|---|---|
| LMArena Text: science | 1415 | 1404 | Step 3.5 Flash |
| LMArena Text: medicine and healthcare | 1408 | 1374 | Step 3.5 Flash |
| LMArena Text: legal and government | 1408 | 1383 | Step 3.5 Flash |
| LMArena Text: business and finance | 1394 | 1381 | Step 3.5 Flash |
| Neither model has a result on the other 13 boards here | |||
Web designDirectional onlyPublic boards, shown as published, kept out of the index6 boards, none shared
| Benchmark | Step 3.5 Flash | Solar Pro 4 | Leader |
|---|---|---|---|
| Design Arena: websites | Not measured | 1177 | Only Solar Pro 4 measured |
| Design Arena: UI components | Not measured | 1150 | Only Solar Pro 4 measured |
| Design Arena: game dev | Not measured | 1170 | Only Solar Pro 4 measured |
| Design Arena: data viz | Not measured | 1177 | Only Solar Pro 4 measured |
| Design Arena: 3D | Not measured | 1178 | Only Solar Pro 4 measured |
| Design Arena: all code categories | Not measured | 1182 | Only Solar Pro 4 measured |
| Neither model has a result on the other 3 boards here | |||
GeneralLike-for-likePublic boards, shown as published, kept out of the index162
| Benchmark | Step 3.5 Flash | Solar Pro 4 | Leader |
|---|---|---|---|
| IFBench | 66.5% | Not measured | Only Step 3.5 Flash measured |
| Long context reasoning (AA-LCR) | 63.0% | 70.7% | Solar Pro 4 |
| LMArena Text | 1403 | 1388 | Step 3.5 Flash |
| LMArena Text: instruction following | 1385 | 1375 | Step 3.5 Flash |
| LMArena Text: creative writing | 1357 | 1317 | Step 3.5 Flash |
| LMArena Text: English | 1417 | 1414 | Step 3.5 Flash |
| LMArena Text: non-English | 1385 | 1363 | Step 3.5 Flash |
| LMArena Text: Chinese | 1446 | 1422 | Step 3.5 Flash |
| LMArena Text: German | 1405 | 1358 | Step 3.5 Flash |
| LMArena Text: Japanese | 1353 | 1320 | Step 3.5 Flash |
| LMArena Text: Korean | 1351 | 1383 | Solar Pro 4 |
| LMArena Text: French | 1421 | 1400 | Step 3.5 Flash |
| LMArena Text: Spanish | 1419 | 1409 | Step 3.5 Flash |
| LMArena Text: Russian | 1385 | 1357 | Step 3.5 Flash |
| LMArena Text: Polish | 1389 | 1304 | Step 3.5 Flash |
| LMArena Text: multi-turn | 1404 | 1385 | Step 3.5 Flash |
| LMArena Text: longer queries | 1402 | 1382 | Step 3.5 Flash |
| LMArena Text: writing and language | 1372 | 1344 | Step 3.5 Flash |
| LMArena Text: entertainment and media | 1360 | 1332 | Step 3.5 Flash |
| Neither model has a result on the other 27 boards here | |||
Image generationNot comparablePublic boards, shown as published, kept out of the index0 boards, none shared
| Benchmark | Step 3.5 Flash | Solar Pro 4 | Leader |
|---|---|---|---|
| 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
Step 3.5 Flash costs less
Repository review
50K input + 3K output tokens
Step 3.5 Flash costs less
Agent loop
200K input + 10K output tokens
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.
| Specification | StepFun Step 3.5 Flash | Upstage Solar Pro 4 |
|---|---|---|
| Maker | StepFun | Upstage |
| Weights | Open weights | No public weights listed |
| Released | January 29, 2026 | August 10, 2026 |
| Context window | 262K | 524K |
| Input $/Mtok | $0.10 | $0.15 |
| Output $/Mtok | $0.30 | $0.60 |
| Coding index | Not benchmarked | Not benchmarked |
| Independent measurements behind it | 0 | 1 |
| Cost per solved task | Not computable | Not computable |
| Source | OpenRouter listing | OpenRouter listing |
Questions
Is Step 3.5 Flash better than Solar Pro 4 for coding?
Neither model has a coding score yet, so the two cannot be ranked on coding. Step 3.5 Flash has the edge where output tokens cost 2.0x less, and where what matters is LMArena Text: coding or AA Intelligence Index, where it leads.
Which is cheaper, Step 3.5 Flash or Solar Pro 4?
Step 3.5 Flash costs $0.10 per million input tokens and $0.30 per million output tokens; Solar Pro 4 costs $0.15 and $0.60. Cost per solved task is known for neither of them.
Which has the bigger context window, Step 3.5 Flash or Solar Pro 4?
Solar Pro 4, with 524K tokens against 262K.
How many benchmarks is the Step 3.5 Flash vs Solar Pro 4 comparison based on?
32 benchmarks have a result for both models as of October 21, 2026. Step 3.5 Flash's coding index rests on 0 independent benchmarks and Solar Pro 4's on 1. Where only one model has a result, the page says so instead of naming a winner.