Gemini 3.1 Pro vs Grok 4.20
Side-by-side comparison of Gemini 3.1 Pro (Google) and Grok 4.20 (xAI). Exact API pricing per million tokens, context windows, output speed, and total cost on real-world prompts.
Specifications
| Spec | Gemini 3.1 Pro | Grok 4.20 |
|---|---|---|
| Provider | xAI | |
| Model id | gemini-3.1-pro | grok-4.20 |
| Input price (per 1M tokens) | $2.00 | $2.00 |
| Output price (per 1M tokens) | $12.00 | $6.00 |
| Context window | 1,048,576 | 2,000,000 |
| Output speed (tokens/sec) | ~90 | ~75 |
Cost on real prompts
Total cost = (input tokens × input price) + (output tokens × output price). Numbers below use the exact pricing tables published by each provider.
| Scenario | Input | Output | Gemini 3.1 Pro | Grok 4.20 | Cheaper |
|---|---|---|---|---|---|
| Short question + answer | 50 | 150 | $0.001900 | $0.001000 | Grok 4.20 |
| Code review on one file | 500 | 1,500 | $0.019000 | $0.010000 | Grok 4.20 |
| Long document summary | 5,000 | 500 | $0.016000 | $0.013000 | Grok 4.20 |
| Heavy reasoning task | 2,000 | 8,000 | $0.100000 | $0.052000 | Grok 4.20 |
| Full codebase analysis | 50,000 | 10,000 | $0.220000 | $0.160000 | Grok 4.20 |
Want the exact cost for your prompt instead of these examples? Open the cost calculator pre-loaded with both models →
When to pick which
Heuristics derived from the spec table above. Always validate on your own prompts before committing — these are starting points, not verdicts.
Pick Gemini 3.1 Pro for
No clear advantage on the data points we measure. Compare on your actual prompts.
Pick Grok 4.20 for
- •output-heavy workloads — grok-4.20 is meaningfully cheaper per output token
- •tasks needing a larger context window — grok-4.20 fits 2x more tokens than gemini-3.1-pro
Switching between them
For most use cases, switching providers means updating the model id and the request shape if the providers differ. Within the same provider, it's usually a single-line change.
From Gemini 3.1 Pro to Grok 4.20
# Before
model = "gemini-3.1-pro"
# After
model = "grok-4.20"If the providers differ (Google vs xAI), you'll also need to swap the SDK / endpoint URL. Cross-provider migrations usually take 30 minutes to a few hours depending on how many features (streaming, function calling, tool use) you depend on.
Calculate cost on your own prompt
The examples above use generic input/output ratios. For an exact comparison, paste your real prompt into the calculator — it counts tokens with the right tokenizer for each model and shows side-by-side cost.
Open the calculator with both models →