Model comparison
GPT-5.5 Pro vs Grok 4.20 Reasoning
Compare GPT-5.5 Pro vs Grok 4.20 Reasoning API pricing: input/output token costs, cache pricing, context windows, workload estimates, and routing fit.
GPT-5.5 Pro
openai · gpt-5.5-pro
- Input
- $30
- Output
- $180
- Context
- 1.1M
Grok 4.20 Reasoning
xai · grok-4.20-0309-reasoning
- Input
- $1.25
- Output
- $2.5
- Context
- 1M
Quick take
Grok 4.20 Reasoning has the lower input price at $1.25 per 1M input tokens. Grok 4.20 Reasoning is cheaper for the example blended workload below. GPT-5.5 Pro has the larger context window at 1.1M tokens.
Choose GPT-5.5 Pro if...
- GPT-5.5 Pro is safer for long documents, repository analysis, and RAG prompts because it has the larger context window.
- GPT-5.5 Pro is required if images, screenshots, or visual documents are part of the workflow.
Choose Grok 4.20 Reasoning if...
- Grok 4.20 Reasoning is the better default for cost-sensitive traffic and repeated high-volume calls.
- Grok 4.20 Reasoning gives more room for long generated answers, reports, or code output.
Example workload cost
Estimates use input tokens plus 20% output tokens. They exclude provider discounts, cache hits, and tool/search surcharges.
| Workload | GPT-5.5 Pro | Grok 4.20 Reasoning | Cheaper |
|---|---|---|---|
| 1M input + 200K output | $66.00 | $1.75 | Grok 4.20 Reasoning |
| 10M input + 2M output | $660.00 | $17.50 | Grok 4.20 Reasoning |
| 100M input + 20M output | $6,600.00 | $175.00 | Grok 4.20 Reasoning |
Context, output, and capability fit
GPT-5.5 Pro provides the larger context window. Check max output separately when the task needs long reports, code generation, or full-document rewrites.
- GPT-5.5 Pro max output
- 128K
- Grok 4.20 Reasoning max output
- 1M
- GPT-5.5 Pro features
- prompt caching, function calling, vision
- Grok 4.20 Reasoning features
- prompt caching, function calling
Risk notes for GPT-5.5 Pro
- High output price: cap max tokens for verbose generation workloads.
Risk notes for Grok 4.20 Reasoning
- No major capability risk is flagged in this snapshot, but provider pages should still be verified before production routing.
Routing tags
frontierpremiumreasoningcodingagentslong-contextmultimodalcache-friendlyrag