Step 3.5 Flash
StepFun released 2026-01-29
$0.150 per million tokens, balanced
No independent quality score.
No benchmark we track has measured this model. That is not the same as measuring it and finding it wanting — we simply cannot rank it, so we do not.
Every price dimension
| Input | $0.100/M |
|---|---|
| Output | $0.300/M |
Independent scores
| LMArena Elo | 1403.8default |
|---|
Sources are listed separately rather than averaged. Across the 62 models both have scored they correlate at r = 0.806 — close agreement overall, but four models rank very differently between them, and a blended score would hide exactly those.
Capability
| Context window | 262K |
|---|---|
| Max output | 66K |
| Input modes | text |
| Tool use | yes |
| Reasoning | always on |
Provenance
| Price source | openrouter.ai |
|---|---|
| Fetched | 2026-08-24 |
| Quality data | unrated |
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....