Grok 4.1 Fast vs Step 3.5 Flash
Grok 4.1 Fast comes out ahead, 71 to 62 on our weighted score, though Step 3.5 Flash is 45% cheaper per token.
- Our pick
xAIGrok 4.1 Fast
71/100- ECI—
- Price$0.20 / $0.50
- Context2M
StepFunStep 3.5 Flash
62/100- ECI—
- Price$0.10 / $0.30
- Context256K
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Make it a three-way comparison.
Grok 4.1 Fast is our pick
Grok 4.1 Fast is the better all-round choice, scoring 71/100 against Step 3.5 Flash (62). It leads on inputs & features and context window. Step 3.5 Flash wins on price. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
- CapabilityNot enough dataNo independent benchmark covers every model here yet
- Lowest priceStep 3.5 FlashStep 3.5 Flash $0.15 · Grok 4.1 Fast $0.275 per 1M tokens (3:1 blend)
- Longest contextGrok 4.1 FastGrok 4.1 Fast 2,000,000 · Step 3.5 Flash 256,000 tokens
- Widest inputsGrok 4.1 FastGrok 4.1 Fast: Text, Images · Step 3.5 Flash: Text
- Self-hostingStep 3.5 FlashPublishes downloadable weights
| Measure | Weight | Grok 4.1 Fast | Step 3.5 Flash |
|---|---|---|---|
| Price | 50% | 76 | 89 |
| Inputs & features | 30% | 60 | 35 |
| Context window | 20% | 72 | 36 |
| Overall | 100% | 71/100 | 62/100 |
Left out because at least one model lacks the data: capability. The remaining weights were rescaled.
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Grok 4.1 FastxAI | Step 3.5 FlashStepFun |
|---|---|---|
| Capability | ||
| Capabilities Index (ECI) | — | — |
| ECI rank | — | — |
| Price per million tokens | ||
| Input | $0.20 | $0.10 (best) |
| Output | $0.50 | $0.30 (best) |
| Cached input | — | $0.02 |
| Blended (3:1) | $0.275 | $0.15 (best) |
| Long-context rate | Same rate | Same rate |
| Price source | Median of 2 providers | Official StepFun (Global) API |
| Limits | ||
| Context window | 2,000,000 tokens (best) | 256,000 tokens |
| Max output | 30,000 tokens | 256,000 tokens (best) |
| Inputs and features | ||
| Text | Yes | Yes |
| Images | Yes | No |
| PDFs | No | No |
| Audio | No | No |
| Video | No | No |
| Reasoning | No | Yeslow · high |
| Tool calling | Yes | Yes |
| Structured output | Yes | No |
| Availability | ||
| Weights | Proprietary | Open |
| API model ID | — | step-3.5-flash |
| API providers | 2 | 8 (best) |
| Released | Nov 19, 2025 | Jan 29, 2026 |
| Knowledge cutoff | — | Jan 2025 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Grok 4.1 Fast$3.00
- Step 3.5 Flash$1.60
Which should you choose?
Which is better: Grok 4.1 Fast or Step 3.5 Flash?
Grok 4.1 Fast is the better all-round choice, scoring 71/100 against Step 3.5 Flash (62). It leads on inputs & features and context window. Step 3.5 Flash wins on price. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
Which is cheaper, Grok 4.1 Fast or Step 3.5 Flash?
Step 3.5 Flash is cheaper at $0.10 input / $0.30 output per million tokens (official StepFun (Global) API price). Grok 4.1 Fast costs $0.20 input / $0.50 output per million tokens (median across 2 API providers). At a typical mix of three input tokens to one output token, that is $0.15 per million tokens for Step 3.5 Flash versus $0.275 for Grok 4.1 Fast (1.8× as much).
Which scores higher on benchmarks?
There is no independent benchmark that covers both models yet. Grok 4.1 Fast has not been scored yet and Step 3.5 Flash has not been scored yet.
Which is better for coding?
There are no published SWE-bench Verified results for Grok 4.1 Fast and Step 3.5 Flash yet, so there is no like-for-like coding score. Test both on a sample of your own tasks. Both support tool calling for agent workflows.
Which has the bigger context window?
Grok 4.1 Fast has the largest context window at 2,000,000 tokens, against 256,000 for Step 3.5 Flash. Maximum output per response: Grok 4.1 Fast up to 30,000, Step 3.5 Flash up to 256,000 tokens.
Which can read images, PDFs, audio or video?
Grok 4.1 Fast accepts text and images; Step 3.5 Flash accepts text. Grok 4.1 Fast handles the widest range of inputs.
Are any of these open source?
Step 3.5 Flash publishes its weights and can be self-hosted; Grok 4.1 Fast is proprietary.
Which is newer?
Step 3.5 Flash is the newest, released Jan 29, 2026. Grok 4.1 Fast came out Nov 19, 2025. Knowledge cutoff: Step 3.5 Flash Jan 2025.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
