Grok 4 Fast Reasoning vs Step 3.7 Flash
Grok 4 Fast Reasoning (2025) and Step 3.7 Flash (2026) are frontier-tier reasoning models from xAI and StepFun. Grok 4 Fast Reasoning ships a 2m-token context window, while Step 3.7 Flash ships a 256k-token context window. On pricing, Step 3.7 Flash costs $0.20/1M input tokens versus $1.25/1M for the alternative. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.
Step 3.7 Flash is ~525% cheaper at $0.20/1M; pay for Grok 4 Fast Reasoning only for long-context analysis.
Decision scorecard
Local evidence first| Signal | Grok 4 Fast Reasoning | Step 3.7 Flash |
|---|---|---|
| Best for | reasoning-heavy apps, multimodal apps, and long-context analysis | reasoning-heavy apps, multimodal apps, and tool-calling agents |
| Decision fit | Long context and Vision | Coding, RAG, and Agents |
| Context window | 2m | 256k |
| Cheapest output | $2.50/1M tokens | $1.15/1M tokens |
| Provider routes | 2 tracked | 3 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- Grok 4 Fast Reasoning has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Local decision data tags Grok 4 Fast Reasoning for Long context and Vision.
- Step 3.7 Flash has the lower cheapest tracked output price at $1.15/1M tokens.
- Step 3.7 Flash has broader tracked provider coverage for fallback and procurement flexibility.
- Step 3.7 Flash uniquely exposes Function calling, Tool use, and Structured outputs in local model data.
- Local decision data tags Step 3.7 Flash for Coding, RAG, and Agents.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
Grok 4 Fast Reasoning
$1,625
Cheapest tracked route/tier: xAI Console
Step 3.7 Flash
$448
Cheapest tracked route/tier: StepFun
Estimated monthly gap: $1,178. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- No overlapping tracked provider route is sourced for Grok 4 Fast Reasoning and Step 3.7 Flash; plan for SDK, billing, or endpoint changes.
- Step 3.7 Flash is $1.35/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Step 3.7 Flash adds Function calling, Tool use, and Structured outputs in local capability data.
- No overlapping tracked provider route is sourced for Step 3.7 Flash and Grok 4 Fast Reasoning; plan for SDK, billing, or endpoint changes.
- Grok 4 Fast Reasoning is $1.35/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Check replacement coverage for Function calling, Tool use, and Structured outputs before moving production traffic.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-09-01 | 2026-05-29 |
| Context window | 2m | 256k |
| Parameters | — | 198B (11B active) |
| Architecture | decoder only | mixture of experts |
| License | Proprietary | Proprietary |
| Openness | Proprietary | Proprietary |
| Commercial use | Commercial use with conditions | Commercial use with conditions |
| Knowledge cutoff | - | - |
Pricing and availability
| Pricing attribute | Grok 4 Fast Reasoning | Step 3.7 Flash |
|---|---|---|
| Input price | $1.25/1M tokens | $0.20/1M tokens |
| Output price | $2.50/1M tokens | $1.15/1M tokens |
| Providers |
Capabilities
| Capability | Grok 4 Fast Reasoning | Step 3.7 Flash |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | Yes |
| Reasoning | Yes | Yes |
| Function calling | No | Yes |
| Tool use | No | Yes |
| Structured outputs | No | Yes |
| Code execution | No | No |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on function calling: Step 3.7 Flash, tool use: Step 3.7 Flash, and structured outputs: Step 3.7 Flash. Both models share vision, multimodal input, and reasoning mode, so the practical split is not just feature count. Use those differences to decide whether the page is about raw model quality, agentic coding support, multimodal ingestion, or predictable structured API behavior.
For cost, Grok 4 Fast Reasoning lists $1.25/1M input and $2.50/1M output tokens on the cheapest tracked provider, while Step 3.7 Flash lists $0.20/1M input and $1.15/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Step 3.7 Flash lower by about $1.14 per million blended tokens. Availability is 2 providers versus 3, so concentration risk also matters.
Choose Grok 4 Fast Reasoning when long-context analysis and larger context windows are central to the workload. Choose Step 3.7 Flash when vision-heavy evaluation, lower input-token cost, and broader provider choice are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship. This keeps the decision grounded in measurable tradeoffs instead of brand-level assumptions.
FAQ
Which has a larger context window, Grok 4 Fast Reasoning or Step 3.7 Flash?
Grok 4 Fast Reasoning supports 2m tokens, while Step 3.7 Flash supports 256k tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Which is cheaper, Grok 4 Fast Reasoning or Step 3.7 Flash?
Step 3.7 Flash is cheaper on tracked token pricing. Grok 4 Fast Reasoning costs $1.25/1M input and $2.50/1M output tokens. Step 3.7 Flash costs $0.20/1M input and $1.15/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is Grok 4 Fast Reasoning or Step 3.7 Flash open source?
Grok 4 Fast Reasoning is listed under Proprietary. Step 3.7 Flash is listed under Proprietary. License labels affect whether you can self-host, redistribute weights, or rely only on hosted APIs, so confirm the upstream license before deployment.
Which is better for vision, Grok 4 Fast Reasoning or Step 3.7 Flash?
Both Grok 4 Fast Reasoning and Step 3.7 Flash expose vision. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.
Which is better for multimodal input, Grok 4 Fast Reasoning or Step 3.7 Flash?
Both Grok 4 Fast Reasoning and Step 3.7 Flash expose multimodal input. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.
Where can I run Grok 4 Fast Reasoning and Step 3.7 Flash?
Grok 4 Fast Reasoning is available on Microsoft Foundry and xAI Console. Step 3.7 Flash is available on StepFun, OpenRouter, and NVIDIA NIM. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
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Last reviewed: 2026-05-29. Data sourced from public model cards and provider documentation.