GPT-5.1-Codex-Max vs Step 3.5 Flash
How do these models stack up? Below is an expert side-by-side comparison of specifications, context window capacity, live pricing per million tokens, and standardized benchmark scores for GPT-5.1-Codex-Max and Step 3.5 Flash.
GPT-5.1-Codex-Max
GPT-5.1-Codex-Max is OpenAI’s latest agentic coding model, designed for long-running, high-context software development tasks. It is based on an updated version of the 5.1 reasoning stack and trained on agentic...
Step 3.5 Flash
Step 3.5 Flash is StepFun's most capable open-source foundation model. Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parameters per token....
Technical Specifications
| Specification | GPT-5.1-Codex-Max | Step 3.5 Flash |
|---|---|---|
| Provider | OpenAI | StepFun |
| Context Window | 400,000 tokens | 262,144 tokens |
| Agent Suitability | N/A | N/A |
| Time to First Token (TTFT) | N/A | N/A |
| Deployment Model | managed api | managed api |
| Production Stability | stable | stable |
| API Available | Yes | Yes |
| Released Date | 2025-12-04 | 2026-01-29 |
API Pricing Comparison
Input Price per Million Tokens
GPT-5.1-Codex-Max
$1.25
Step 3.5 Flash
$0.10
Output Price per Million Tokens
GPT-5.1-Codex-Max
$10.00
Step 3.5 Flash
$0.30
Want to test both models live?
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Benchmark Performance Metrics
Scores show the raw performance percentages verified across key evaluation suites. Higher bars indicate superior accuracy and capability in that domain.
GPT-5.1-Codex-Max Quirks & Gotchas
No developer gotchas reported.
Step 3.5 Flash Quirks & Gotchas
No developer gotchas reported.