GPT-5.5 Pro vs Grok 4 Heavy
GPT-5.5 Pro (2026) and Grok 4 Heavy (2025) are frontier reasoning models from OpenAI and xAI. GPT-5.5 Pro ships a 1M-token context window, while Grok 4 Heavy ships a 256k-token context window. On SWE-bench Pro, GPT-5.5 Pro leads by 18.8 pts. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit. It focuses on practical selection signals rather than broad model-family marketing.
GPT-5.5 Pro is safer overall; choose Grok 4 Heavy when provider fit matters.
Specs
| Released | 2026-04-23 | 2025-07-09 |
| Context window | 1M | 256k |
| Parameters | — | — |
| Architecture | decoder only | - |
| License | Proprietary | Proprietary |
| Knowledge cutoff | - | - |
Pricing and availability
| GPT-5.5 Pro | Grok 4 Heavy | |
|---|---|---|
| Input price | $30/1M tokens | - |
| Output price | $180/1M tokens | - |
| Providers | - |
Capabilities
| GPT-5.5 Pro | Grok 4 Heavy | |
|---|---|---|
| Vision | ||
| Multimodal | ||
| Reasoning | ||
| Function calling | ||
| Tool use | ||
| Structured outputs | ||
| Code execution |
Benchmarks
| Benchmark | GPT-5.5 Pro | Grok 4 Heavy |
|---|---|---|
| SWE-bench Pro | 58.6 | 39.8 |
Deep dive
On shared benchmark coverage, SWE-bench Pro has GPT-5.5 Pro at 58.6 and Grok 4 Heavy at 39.8, with GPT-5.5 Pro ahead by 18.8 points. The largest visible gap is 18.8 points on SWE-bench Pro, which matters most when that benchmark mirrors your workload. Treat isolated benchmark wins as directional, because provider routing, prompt style, and tool access can move real application results.
The capability footprint differs most on vision: GPT-5.5 Pro, reasoning mode: GPT-5.5 Pro, function calling: GPT-5.5 Pro, tool use: GPT-5.5 Pro, structured outputs: GPT-5.5 Pro, and code execution: GPT-5.5 Pro. Both models share multimodal input, 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.
Pricing coverage is uneven: GPT-5.5 Pro has $30/1M input tokens and Grok 4 Heavy has no token price sourced yet. Provider availability is 1 tracked routes versus 0. Treat unknown pricing as an integration gap, then verify the route you will actually call before estimating production spend.
Choose GPT-5.5 Pro when coding workflow support, larger context windows, and broader provider choice are central to the workload. Choose Grok 4 Heavy when provider fit are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship.
FAQ
Which has a larger context window, GPT-5.5 Pro or Grok 4 Heavy?
GPT-5.5 Pro supports 1M tokens, while Grok 4 Heavy supports 256k tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Is GPT-5.5 Pro or Grok 4 Heavy open source?
GPT-5.5 Pro is listed under Proprietary. Grok 4 Heavy 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, GPT-5.5 Pro or Grok 4 Heavy?
GPT-5.5 Pro has the clearer documented vision signal in this comparison. If vision is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Which is better for multimodal input, GPT-5.5 Pro or Grok 4 Heavy?
Both GPT-5.5 Pro and Grok 4 Heavy expose multimodal input. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.
Which is better for reasoning mode, GPT-5.5 Pro or Grok 4 Heavy?
GPT-5.5 Pro has the clearer documented reasoning mode signal in this comparison. If reasoning mode is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run GPT-5.5 Pro and Grok 4 Heavy?
GPT-5.5 Pro is available on OpenAI API. Grok 4 Heavy is available on the tracked providers still being sourced. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
Continue comparing
Last reviewed: 2026-04-24. Data sourced from public model cards and provider documentation.