Comparison · prices as of 2026-07-04 · re-verified 2026-08-18
GPT-5 mini vs Grok 4 Fast
On price alone, Grok 4 Fast (xAI) runs about 57% cheaper than GPT-5 mini 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 mini | Grok 4 Fast |
|---|---|---|
| Input / MTok | $0.25 | $0.20 |
| Output / MTok | $2 | $0.50 |
| Context window | 400K | 2M |
| Max output | 128K | 30K |
| Class | workhorse | fast / lightweight |
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 mini | Grok 4 Fast | Cheaper |
|---|---|---|---|
| Light — chatbot 0.5K in / 0.2K out · 200 req/day | $3.15 | $1.20 | Grok 4 Fast |
| Typical — assistant 2K in / 0.5K out · 1K req/day | $45.00 | $19.50 | Grok 4 Fast |
| Heavy — RAG / agent 8K in / 2K out · 5K req/day | $900 | $390 | Grok 4 Fast |
Which should you pick?
- Cheapest overall: Grok 4 Fast — about 57% less per month on a typical assistant workload.
- Grok 4 Fast is cheaper on both input and output, so it stays cheaper whether your workload is prompt-heavy or generation-heavy.
- Largest context window: Grok 4 Fast at 2M tokens vs 400K — the one to pick if you feed in whole documents or codebases.
- Different classes: GPT-5 mini is a workhorse model, Grok 4 Fast is a fast / lightweight model — expect GPT-5 mini to be stronger on hard reasoning and Grok 4 Fast to be faster and cheaper to run.
Frequently asked questions
Is GPT-5 mini or Grok 4 Fast cheaper?
Grok 4 Fast is cheaper — roughly 57% less per month on a typical assistant workload (2K input + 500 output tokens, 1,000 requests/day).
What do GPT-5 mini and Grok 4 Fast cost per million tokens?
GPT-5 mini is $0.25 per million input tokens and $2 per million output. Grok 4 Fast is $0.20 input and $0.50 output. Prices are first-party API list rates as of 2026-07-04.
Which has the larger context window, GPT-5 mini or Grok 4 Fast?
Grok 4 Fast does, at 2M tokens versus 400K for GPT-5 mini.
When should I choose GPT-5 mini over Grok 4 Fast?
Choose GPT-5 mini when you need the extra capability of its workhorse class; drop to Grok 4 Fast when speed and cost matter more than peak quality.
Related comparisons
Sources: OpenAI pricing · xAI pricing. Run your own numbers in the cost calculator.