Grok 4.20 vs Grok 4.1 Fast
Side-by-side comparison of Grok 4.20 (xAI) and Grok 4.1 Fast (xAI). Exact API pricing per million tokens, context windows, output speed, and total cost on real-world prompts.
Specifications
| Spec | Grok 4.20 | Grok 4.1 Fast |
|---|---|---|
| Provider | xAI | xAI |
| Model id | grok-4.20 | grok-4.1-fast |
| Input price (per 1M tokens) | $2.00 | $0.20 |
| Output price (per 1M tokens) | $6.00 | $0.50 |
| Context window | 2,000,000 | 2,000,000 |
| Output speed (tokens/sec) | ~75 | ~180 |
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 | Grok 4.20 | Grok 4.1 Fast | Cheaper |
|---|---|---|---|---|---|
| Short question + answer | 50 | 150 | $0.001000 | $0.000085 | Grok 4.1 Fast |
| Code review on one file | 500 | 1,500 | $0.010000 | $0.00085 | Grok 4.1 Fast |
| Long document summary | 5,000 | 500 | $0.013000 | $0.001250 | Grok 4.1 Fast |
| Heavy reasoning task | 2,000 | 8,000 | $0.052000 | $0.004400 | Grok 4.1 Fast |
| Full codebase analysis | 50,000 | 10,000 | $0.160000 | $0.015000 | Grok 4.1 Fast |
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 Grok 4.20 for
No clear advantage on the data points we measure. Compare on your actual prompts.
Pick Grok 4.1 Fast for
- •output-heavy workloads — grok-4.1-fast is meaningfully cheaper per output token
- •input-heavy workloads — grok-4.1-fast is cheaper per input token
- •latency-sensitive UX — grok-4.1-fast streams faster (~180 vs ~75 tok/s)
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 Grok 4.20 to Grok 4.1 Fast
# Before
model = "grok-4.20"
# After
model = "grok-4.1-fast"If the providers differ (xAI 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 →