GPT-5.5 Instant vs Grok 4
GPT-5.5 Instant (2026) and Grok 4 (2026) are frontier reasoning models from OpenAI and xAI. GPT-5.5 Instant ships a 400K-token context window, while Grok 4 ships a 256k-token context window. On pricing, GPT-5.5 Instant costs $1.5/1M input tokens versus $3/1M for the alternative. 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 Instant is ~100% cheaper at $1.5/1M; pay for Grok 4 only for coding workflow support.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-05-05 | 2026-03-01 |
| Context window | 400K | 256k |
| Parameters | — | — |
| Architecture | decoder only | decoder only |
| License | Proprietary | Proprietary |
| Knowledge cutoff | 2025-08 | - |
Pricing and availability
| Pricing attribute | GPT-5.5 Instant | Grok 4 |
|---|---|---|
| Input price | $1.5/1M tokens | $3/1M tokens |
| Output price | $6/1M tokens | $15/1M tokens |
| Providers |
Capabilities
| Capability | GPT-5.5 Instant | Grok 4 |
|---|---|---|
| Vision | Yes | No |
| Multimodal | Yes | Yes |
| Reasoning | No | Yes |
| Function calling | Yes | Yes |
| Tool use | Yes | Yes |
| Structured outputs | Yes | Yes |
| Code execution | Yes | Yes |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on vision: GPT-5.5 Instant and reasoning mode: Grok 4. Both models share multimodal input, function calling, tool use, and structured outputs, 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, GPT-5.5 Instant lists $1.5/1M input and $6/1M output tokens, while Grok 4 lists $3/1M input and $15/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts GPT-5.5 Instant lower by about $3.75 per million blended tokens. Availability is 1 providers versus 3, so concentration risk also matters.
Choose GPT-5.5 Instant when coding workflow support, larger context windows, and lower input-token cost are central to the workload. Choose Grok 4 when coding workflow support 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. It also helps separate model capability from provider packaging, which can change cost and latency.
FAQ
Which has a larger context window, GPT-5.5 Instant or Grok 4?
GPT-5.5 Instant supports 400K tokens, while Grok 4 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, GPT-5.5 Instant or Grok 4?
GPT-5.5 Instant is cheaper on tracked token pricing. GPT-5.5 Instant costs $1.5/1M input and $6/1M output tokens. Grok 4 costs $3/1M input and $15/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is GPT-5.5 Instant or Grok 4 open source?
GPT-5.5 Instant is listed under Proprietary. Grok 4 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 Instant or Grok 4?
GPT-5.5 Instant 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 Instant or Grok 4?
Both GPT-5.5 Instant and Grok 4 expose multimodal input. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Where can I run GPT-5.5 Instant and Grok 4?
GPT-5.5 Instant is available on OpenAI API. Grok 4 is available on Microsoft Foundry, OpenRouter, and Replicate API. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
Continue comparing
Last reviewed: 2026-05-11. Data sourced from public model cards and provider documentation.