Side-by-side technical and economic comparison between Google's Gemini 3.1 Pro Preview and xAI's Grok 2.
• Grok 2: Classified as a Legacy Reference model (Generally Available).
| Metric | Gemini 3.1 Pro Preview | Grok 2 | Advantage |
|---|---|---|---|
| Provider Organization | xAI | — | |
| Standard Input / 1M | $2.00 | $2.00 | Identical |
| Cached Input / 1M | $0.20 | None | Gemini 3.1 Pro Preview lower |
| Output / 1M | $12.00 | $10.00 | Grok 2 lower |
| Context Window | 1.05M | 128k | Gemini 3.1 Pro Preview (1.05M) |
| Max Generation Tokens | 16.4k | 8.2k | Gemini 3.1 Pro Preview |
| Tokenizer Family | Google Gemini SentencePiece (256k vocabulary) | xAI Byte-level BPE (~131k vocabulary) | — |
Opt for Gemini 3.1 Pro Preview when your engineering requirements prioritize Google's ecosystem, specific tokenizer efficiencies (Calibrated Gemini Tokenizer (±4%)), or when your expected prompt-to-completion ratios favor its $2/M input rate.
Opt for Grok 2 when looking for xAI's tooling integration, specific context window depth (128k tokens), or when output generation volume favors its $10/M rate.