Head-to-head comparison
Gemini 3.1 Pro Preview (Google) and Gemma 4 31B (Google) compared on the ModelCap Index, API price, context window, provider availability, weight access and every public benchmark board they share. Figures are the same ones shown on the live rankings; nothing here is a hidden score.
Snapshot as of 6 November 2026
As of 6 November 2026, Gemini 3.1 Pro Preview holds the stronger ModelCap Index position (#10 vs #37); Gemma 4 31B is 30× cheaper per output token ($0.40/1M vs $12.00/1M); Gemini 3.1 Pro Preview offers the longer context window (1M vs 262K tokens); and Gemma 4 31B ships open weights.
Evidence: 3 public benchmark observations across 3 boards · 2 public benchmark observations across 2 boards. Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.
Scores are the sources' own published figures for each model's best evaluated configuration; ModelCap never re-runs a benchmark.
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Gemini 3.1 Pro Preview ranks higher on the ModelCap Index as of 6 November 2026: #10 against #37. That is a capability ranking built from public benchmark evidence with published uncertainty; whether it is "better" for you also depends on price, context and where you can run it. Their published uncertainty intervals overlap, so the rank difference alone does not establish a reliable capability advantage for your workload.
Gemma 4 31B is cheaper on output tokens: $0.40/1M against $12.00/1M. Input tokens are $2.00/1M for Gemini 3.1 Pro Preview and $0.20/1M for Gemma 4 31B. Prices are the lowest listed API offer ModelCap observed, in USD per million tokens. For 1,000 requests with 2,000 input and 500 output tokens each (2M input + 0.5M output), the listed-rate estimate is $10.00 for Gemini 3.1 Pro Preview versus $0.60 for Gemma 4 31B. Gemma 4 31B costs 94.0% less in this scenario. This excludes caching, batch discounts, prompt-length tiers, tool charges and retries; verify the selected endpoint before budgeting.
Gemini 3.1 Pro Preview has the larger context window: 1M tokens against 262K. OpenRouter catalogue or provider-endpoint declaration. Limits can vary by provider and prompt length; a model-wide maximum has not been independently verified.
Arena coding: Gemini 3.1 Pro Preview 1521, Gemma 4 31B 1502 — Gemini 3.1 Pro Preview leads.
Gemini 3.1 Pro Preview: No linked weights. Gemma 4 31B: Open weights. Open weights mean the checkpoint can be downloaded and self-hosted under its licence. A missing weight link does not identify every API or chat product that offers a model.
ModelCap currently lists 2 API providers for Gemini 3.1 Pro Preview and 16 for Gemma 4 31B, from the OpenRouter catalogue snapshot the site serves; each model page lists the providers and their prices.
Every figure and ModelCap Index position comes from the same published snapshot dated 6 November 2026. Publication and page updates happen separately; use the snapshot date shown on the page.