Step-3.5-Flash vs o4 Mini
API pricing, benchmark indices and specs — updated 19 October 2026.
stepfun-ai · A · Open weights
Params
199.4 B
Context
262,144
30d
264 K
apache-2.0 · commercial OK
openai · B · API-only
Input / 1M
$1.10
Output / 1M
$4.40
AA index
16.7
proprietary · 200K context
Specification comparison
Differences are highlighted; identical values are muted.
| Specification | Step-3.5-Flash | o4 Mini |
|---|---|---|
| Deployment | Open weights · also via API | API-only (closed weights) |
| Parameters | 199.4 B | n/a — API-only |
| Architecture | Step3p5ForCausalLM | n/a — API-only |
| Context length | 262,144 | 200,000 |
| Licence | apache-2.0 | Proprietary |
| Commercial use | Allowed | Per API terms |
| Languages | — | n/a — API-only |
| Downloads 30d | 264,309 | n/a — API-only |
| Downloads all time | 1.9 M | n/a — API-only |
| Quantizations on the Hub | SAFETENSORS | n/a — API-only |
| Gated | No | n/a — API-only |
| First seen on the Hub | 2026-02-01 | n/a — API-only |
| API input price / 1M tokens | $0.10 | $1.10 |
| API output price / 1M tokens | $0.30 | $4.40 |
| Est. cost per 1M input + 1M output tokens | $0.40 | $5.50 |
| Cached input / 1M tokens | — | $0.28 |
| AA Intelligence Index | 17 | 16.7 |
| AA Coding Index | — | — |
| AA Agentic Index | — | — |
| Max output tokens | 65,536 | 100,000 |
| API providers | 1 | 1 |
| Tool calling | Yes | Yes |
| Reasoning mode | Yes | Yes |
API cost
Estimated cost of 1M input + 1M output tokens via OpenRouter
Step-3.5-Flash
$0.40
o4 Mini
$5.50
Step-3.5-Flash is 13.8× cheaper at list price.
VRAM side by side
On RTX 4090 · 24 GB · 8K context unless noted
Step-3.5-Flash · fp16 @ 256K ctx
1,396.2 GB / 24 GB