Comparison · prices as of 2026-08-30 · re-verified 2026-10-05
GPT-5 nano vs Grok 4 Fast
On price alone, GPT-5 nano (OpenAI) runs about 92% cheaper than Grok 4 Fast 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 nano | Grok 4 Fast |
|---|---|---|
| Input / MTok | $0.05 | $1.25 |
| Output / MTok | $0.40 | $2.50 |
| Context window | 400K | 2M |
| Max output | 128K | 30K |
| Class | fast / lightweight | 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 nano | Grok 4 Fast | Cheaper |
|---|---|---|---|
| Light — chatbot 0.5K in / 0.2K out · 200 req/day | $0.63 | $6.75 | GPT-5 nano |
| Typical — assistant 2K in / 0.5K out · 1K req/day | $9.00 | $113 | GPT-5 nano |
| Heavy — RAG / agent 8K in / 2K out · 5K req/day | $180 | $2,250 | GPT-5 nano |
Which should you pick?
- Cheapest overall: GPT-5 nano — about 92% less per month on a typical assistant workload.
- GPT-5 nano 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.
Frequently asked questions
Is GPT-5 nano or Grok 4 Fast cheaper?
GPT-5 nano is cheaper — roughly 92% less per month on a typical assistant workload (2K input + 500 output tokens, 1,000 requests/day).
What do GPT-5 nano and Grok 4 Fast cost per million tokens?
GPT-5 nano is $0.05 per million input tokens and $0.40 per million output. Grok 4 Fast 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 nano or Grok 4 Fast?
Grok 4 Fast does, at 2M tokens versus 400K for GPT-5 nano.
When should I choose Grok 4 Fast over GPT-5 nano?
Both are fast / lightweight-class models, so choose Grok 4 Fast when it measurably wins on your own evals or you prefer its provider (xAI); otherwise GPT-5 nano does the same job for less.
Related comparisons
Sources: OpenAI pricing · xAI pricing. Run your own numbers in the cost calculator.