Compare / head-to-head
GPT-5.5 ProvsGrok 4 Fast Reasoning
GPT-5.5 Pro leads 2 of 2 shared benchmarks. Grok 4 Fast Reasoning is 300x cheaper per token. 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
2 – 0
GPT-5.5 Pro leads
Cheaper per token
Grok 4 Fast Reasoning
300x cheaper, input + output
Larger context
Grok 4 Fast Reasoning
2M tokens
Provider uptime (30d)
94.2446% · —
OpenAI · xAI
GPT-5.5 Pro
OpenAI · released 2026-04-23
textvision
Grok 4 Fast Reasoning
xAI · released 2025-09-19
text
Quality
Benchmark matrix
2 shared · 6 only GPT-5.5 Pro · 10 only Grok 4 Fast Reasoning| Benchmark | GPT-5.5 Pro | Grok 4 Fast Reasoning | Δ | Edge |
|---|---|---|---|---|
| Reported by both · 2 | ||||
| Humanity's Last Exam (no tools) | 43.1% ↗ | 20% ↗ | +23.1 pt | GPT-5.5 Pro |
| BrowseComp | 90.1% ↗ | 44.9% ↗ | +45.2 pt | GPT-5.5 Pro |
| Only GPT-5.5 Pro reports · 6 | ||||
| FrontierMath Tier 1-3 | 52.4% ↗ | not reported | — | — |
| FrontierMath Tier 4 | 39.6% ↗ | not reported | — | — |
| FrontierMath Tier 4 v2 (Epoch AI run) | 78% ↗epoch | not reported | — | — |
| FrontierMath Tiers 1-3 v2 (Epoch AI run) | 87.7% ↗epoch | not reported | — | — |
| GDPval (wins or ties) | 82.3% ↗ | not reported | — | — |
| Humanity's Last Exam (with tools) | 57.2% ↗ | not reported | — | — |
| Only Grok 4 Fast Reasoning reports · 10 | ||||
| GPQA Diamond | not reported | 85.7% ↗ | — | — |
| AIME 2025 | not reported | 92% ↗ | — | — |
| BrowseComp (zh) | not reported | 51.2% ↗ | — | — |
| HMMT 2025 (no tools) | not reported | 93.3% ↗ | — | — |
| LiveCodeBench (Jan-May) | not reported | 80% ↗ | — | — |
| Reka Research Eval | not reported | 66% ↗ | — | — |
| Search Arena Elo | not reported | 1163 ↗ | — | — |
| SimpleQA | not reported | 95% ↗ | — | — |
| X Bench Deepsearch (zh) | not reported | 74% ↗ | — | — |
| X Browse | not reported | 58% ↗ | — | — |
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 GPT-5.5 Pro minus Grok 4 Fast Reasoning 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 | GPT-5.5 Pro | Grok 4 Fast Reasoning | Edge |
|---|---|---|---|
| Context window | 1.1M tokens | 2M tokens | Grok 4 Fast Reasoning |
| Max output | 128K tokens | — | — |
| Input price / 1M | $30 ↗ | $0.2 ↗ | Grok 4 Fast Reasoning |
| Output price / 1M | $180 ↗ | $0.5 ↗ | Grok 4 Fast Reasoning |
| Cached input / 1M | — | $0.05 ↗ | — |
| Input + output / 1M Lower is cheaper. List prices; batch, tool and regional fees excluded. | $210 | $0.7 | Grok 4 Fast Reasoning |
| Modalities | text · vision | text | GPT-5.5 Pro |
| Released | 2026-04-23 | 2025-09-19 | — |
| Cited benchmark scores | 8 | 12 | — |
Reliability
Provider status
Last 60 days · refreshed daily on this page · live on /statusMore matchups
GPT-5.5 Pro vs …
Models sharing the most benchmarksMore matchups
Grok 4 Fast Reasoning vs …
Models sharing the most benchmarksBuilt by Respan
Which one wins on your data?
Public benchmarks are a starting point. Run GPT-5.5 Pro and Grok 4 Fast Reasoning on your own prompts with Respan evals, or route to either through one gateway key with automatic failover.