Compare / head-to-head
Grok 4 Fast ReasoningvsStep 3.5 Flash
Step 3.5 Flash leads 2 of 2 shared benchmarks. Grok 4 Fast Reasoning has the larger context window (2M tokens).
Benchmarks from cited public sources; pricing from official pages; status from official provider feeds.
Shared benchmarks
0 – 2
Step 3.5 Flash leads
Cheaper per token
—
list price, input + output
Larger context
Grok 4 Fast Reasoning
2M tokens
Provider uptime (30d)
— · —
xAI · StepFun
Grok 4 Fast Reasoning
xAI · released 2025-09-19
text
Step 3.5 Flash
StepFun · released 2026-02-12
text
- Context
- 256K
- Max out
- —
- Input /1M
- —
- Output /1M
- —
- Cached /1M
- —
- Scores
- 18 · 5 core
Quality
Benchmark matrix
2 shared · 10 only Grok 4 Fast Reasoning · 15 only Step 3.5 Flash| Benchmark | Grok 4 Fast Reasoning | Step 3.5 Flash | Δ | Edge |
|---|---|---|---|---|
| Reported by both · 2 | ||||
| AIME 2025 | 92% ↗ | 97.3% ↗ | -5.3 pt | Step 3.5 Flash |
| BrowseComp | 44.9% ↗ | 51.6% ↗ | -6.7 pt | Step 3.5 Flash |
| Only Grok 4 Fast Reasoning reports · 10 | ||||
| GPQA Diamond | 85.7% ↗ | not reported | — | — |
| Humanity's Last Exam (no tools) | 20% ↗ | not reported | — | — |
| BrowseComp (zh) | 51.2% ↗ | not reported | — | — |
| HMMT 2025 (no tools) | 93.3% ↗ | not reported | — | — |
| LiveCodeBench (Jan-May) | 80% ↗ | not reported | — | — |
| Reka Research Eval | 66% ↗ | not reported | — | — |
| Search Arena Elo | 1163 ↗ | not reported | — | — |
| SimpleQA | 95% ↗ | not reported | — | — |
| X Bench Deepsearch (zh) | 74% ↗ | not reported | — | — |
| X Browse | 58% ↗ | not reported | — | — |
| Only Step 3.5 Flash reports · 15 | ||||
| SWE-bench Verified | not reported | 74.4% ↗ | — | — |
| AIME 2026 | not reported | 96.7% ↗matharena | — | — |
| LMArena Elo | not reported | 1403.7 ↗ | — | — |
| BrowseComp (with context manager) | not reported | 69% ↗ | — | — |
| BrowseComp-ZH | not reported | 66.9% ↗ | — | — |
| BrowseComp-ZH (with context manager) | not reported | 73.7% ↗ | — | — |
| GAIA (no file) | not reported | 84.5% ↗ | — | — |
| HMMT 2025 (Feb/Nov average) | not reported | 96.2% ↗ | — | — |
| IMOAnswerBench | not reported | 85.4% ↗ | — | — |
| LiveCodeBench v6 | not reported | 86.4% ↗ | — | — |
| ResearchRubrics | not reported | 65.3% ↗ | — | — |
| Tau2-Bench | not reported | 88.2% ↗ | — | — |
| Terminal-Bench 2.0 | not reported | 51% ↗ | — | — |
| xbench-DeepSearch 2025.05 | not reported | 83.7% ↗ | — | — |
| xbench-DeepSearch 2025.10 | not reported | 56.3% ↗ | — | — |
Scores tagged "epoch" or "matharena" are independent runs, used only where the lab has not published its own; ⚠ marks rows MathArena flags as released after the competition. Higher is better on every row. Δ is Grok 4 Fast Reasoning minus Step 3.5 Flash in the benchmark's own unit. "Not reported" means the lab has not published that figure; it is not a zero. ↗ opens the source.
Specs & pricing
Side by side
Official pricing pages and model cards| Spec | Grok 4 Fast Reasoning | Step 3.5 Flash | Edge |
|---|---|---|---|
| Context window | 2M tokens | 256K tokens | Grok 4 Fast Reasoning |
| Max output | — | — | — |
| Input price / 1M | $0.2 ↗ | — | — |
| Output price / 1M | $0.5 ↗ | — | — |
| Cached input / 1M | $0.05 ↗ | — | — |
| Input + output / 1M Lower is cheaper. List prices; batch, tool and regional fees excluded. | $0.7 | — | — |
| Modalities | text | text | Tie |
| Released | 2025-09-19 | 2026-02-12 | — |
| Cited benchmark scores | 12 | 18 | — |
Reliability
Provider status
Last 60 days · refreshed daily on this page · live on /statusMore matchups
Grok 4 Fast Reasoning vs …
Models sharing the most benchmarksMore matchups
Step 3.5 Flash vs …
Models sharing the most benchmarksBuilt by Respan
Which one wins on your data?
Public benchmarks are a starting point. Run Grok 4 Fast Reasoning and Step 3.5 Flash on your own prompts with Respan evals, or route to either through one gateway key with automatic failover.