GPT-6 Luna vs Grok 4 Fast
Both have similar output pricing, while Grok 4 Fast offers a larger context window. Choose GPT-6 Luna or Grok 4 Fast based on the trade-off between cost, context, and the benchmarks that matter for your use case.
| Spec | GPT-6 Luna | Grok 4 Fast |
|---|---|---|
| Provider | OpenAI | ZenMux |
| Input / 1M tokens | $0.10 | $0.20 |
| Output / 1M tokens | $0.50 | $0.50 |
| Context window | 1.1M | 2M |
| Parameters | — | — |
| Open weights | — | No |
| Released | — | Sep 2025 |
| GPQA Diamond score | 90.5 | — |
| LMArena (Chatbot Arena) Elo score | 1392 | 1400 |
| LMArena WebDev Elo score | 1582 | 1159 |
| LMArena Vision Elo score | 1217 | — |
| Epoch Capabilities Index score | 156 | 144 |
FAQ
Is GPT-6 Luna or Grok 4 Fast cheaper?
GPT-6 Luna and Grok 4 Fast have comparable output pricing.
Which has the larger context window, GPT-6 Luna or Grok 4 Fast?
Grok 4 Fast has the larger context window (2M tokens).
Pricing is indicative — confirm with the provider before production use. Highlighted values indicate the better figure for that row.