Side-by-side technical and economic comparison between OpenAI's GPT-5.6 Luna and xAI's Grok 4.6.
| Metric | GPT-5.6 Luna | Grok 4.6 | Advantage |
|---|---|---|---|
| Provider Organization | OpenAI | xAI | — |
| Standard Input / 1M | $0.20 | $2.00 | GPT-5.6 Luna (90% lower) |
| Cached Input / 1M | $0.02 | $0.50 | GPT-5.6 Luna lower |
| Output / 1M | $1.20 | $6.00 | GPT-5.6 Luna lower |
| Context Window | 1.05M | 500k | GPT-5.6 Luna (1.05M) |
| Max Generation Tokens | 16.4k | 128k | Grok 4.6 |
| Tokenizer Family | OpenAI o200k_base (200k vocabulary) | xAI Byte-level BPE (~131k vocabulary) | — |
Opt for GPT-5.6 Luna when your engineering requirements prioritize OpenAI's ecosystem, specific tokenizer efficiencies (Exact BPE (o200k_base)), or when your expected prompt-to-completion ratios favor its $0.2/M input rate.
Opt for Grok 4.6 when looking for xAI's tooling integration, specific context window depth (500k tokens), or when output generation volume favors its $6/M rate.