Grok 4 Fast Reasoning ≤128k vs GPT-5.1 Codex mini
Side-by-side comparison of pricing and capabilities
Grok 4 Fast Reasoning ≤128k
GPT-5.1 Codex mini
Input Price Comparison
| Attribute | Grok 4 Fast Reasoning ≤128k | GPT-5.1 Codex mini |
|---|---|---|
| Provider | xAI | OpenAI |
| Input Price | $0.2 /1M tokens | $0.25 /1M tokens |
| Output Price | $0.5 /1M tokens | $2 /1M tokens |
| Cached Input | $0.050 /1M tokens | $0.025 /1M tokens |
| Context Window | 131K | 400K |
| Type | reasoning | chat |
| Status | current | current |
Capability Comparison
| Capability | Grok 4 Fast Reasoning ≤128k | GPT-5.1 Codex mini |
|---|---|---|
| reasoning | ||
| coding |
Which should you choose?
Budget-conscious: Grok 4 Fast Reasoning ≤128k is 20% cheaper on input tokens ($0.2 vs $0.25 per 1M tokens).
Context-heavy tasks: GPT-5.1 Codex mini offers a larger context window (400K vs 131K), making it better for long documents or conversations.
Capability fit: Grok 4 Fast Reasoning ≤128k supports 1 capabilities (reasoning), while GPT-5.1 Codex mini supports 1 (coding).
Frequently Asked Questions
Which is cheaper: Grok 4 Fast Reasoning ≤128k or GPT-5.1 Codex mini?
Grok 4 Fast Reasoning ≤128k costs $0.2/1M input vs GPT-5.1 Codex mini at $0.25/1M input. Grok 4 Fast Reasoning ≤128k is 20% cheaper on input tokens.
How do output prices compare between Grok 4 Fast Reasoning ≤128k and GPT-5.1 Codex mini?
Grok 4 Fast Reasoning ≤128k output: $0.5/1M, GPT-5.1 Codex mini output: $2/1M. Grok 4 Fast Reasoning ≤128k is more economical for generation-heavy workloads.
What is Grok 4 Fast Reasoning ≤128k best used for?
Grok 4 Fast Reasoning ≤128k is best for budget-conscious applications, high-volume chatbots, and tasks where cost efficiency is the primary concern.
What is GPT-5.1 Codex mini best used for?
GPT-5.1 Codex mini is suited for complex reasoning, analysis, and tasks that benefit from its coding capabilities.