Comparison · prices as of 2026-08-30 · re-verified 2026-10-05
GPT-5.1 vs Grok 4
On price alone, Grok 4 (xAI) runs about 50% cheaper than GPT-5.1 for a typical chat workload (2K input + 500 output tokens, 1,000 requests/day). Whether that's the right trade depends on the capability gap — the breakdown below shows where each one wins.
Price per million tokens
| Spec | GPT-5.1 | Grok 4 |
|---|---|---|
| Input / MTok | $1.25 | $1.25 |
| Output / MTok | $10 | $2.50 |
| Context window | 400K | 256K |
| Max output | 128K | 64K |
| Class | frontier | frontier |
Estimated monthly cost by workload
Same models, three realistic usage levels. The gap between them scales with volume, so the right pick can change as you grow.
| Workload | GPT-5.1 | Grok 4 | Cheaper |
|---|---|---|---|
| Light — chatbot 0.5K in / 0.2K out · 200 req/day | $15.75 | $6.75 | Grok 4 |
| Typical — assistant 2K in / 0.5K out · 1K req/day | $225 | $113 | Grok 4 |
| Heavy — RAG / agent 8K in / 2K out · 5K req/day | $4,500 | $2,250 | Grok 4 |
Which should you pick?
- Cheapest overall: Grok 4 — about 50% less per month on a typical assistant workload.
- Input-heavy work (long-context RAG, summarization): GPT-5.1 wins on input at $1.25/MTok. Output-heavy work (drafting, code generation): Grok 4 wins on output at $2.50/MTok.
- Largest context window: GPT-5.1 at 400K tokens vs 256K — the one to pick if you feed in whole documents or codebases.
Frequently asked questions
Is GPT-5.1 or Grok 4 cheaper?
Grok 4 is cheaper — roughly 50% less per month on a typical assistant workload (2K input + 500 output tokens, 1,000 requests/day).
What do GPT-5.1 and Grok 4 cost per million tokens?
GPT-5.1 is $1.25 per million input tokens and $10 per million output. Grok 4 is $1.25 input and $2.50 output. Prices are first-party API list rates as of 2026-08-30.
Which has the larger context window, GPT-5.1 or Grok 4?
GPT-5.1 does, at 400K tokens versus 256K for Grok 4.
When should I choose GPT-5.1 over Grok 4?
Both are frontier-class models, so choose GPT-5.1 when it measurably wins on your own evals or you prefer its provider (OpenAI); otherwise Grok 4 does the same job for less.
Related comparisons
Sources: OpenAI pricing · xAI pricing. Run your own numbers in the cost calculator.