GPT-5.1 Codex High vs Step-3.5-Flash
Step-3.5-Flash significantly outperforms across most benchmarks. Step-3.5-Flash is 19.6x cheaper per token.
OpenAI · StepFun · Updated for 2026
Which is better?
GPT-5.1 Codex High outperforms in 0 benchmarks, while Step-3.5-Flash is better at 1 benchmark (AIME 2025). Step-3.5-Flash significantly outperforms across most benchmarks.
On price, Step-3.5-Flash is roughly 19.6x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
GPT-5.1 Codex High also accepts a larger context window (400,000 input tokens), making it the stronger choice for long documents and large codebases.
Based on current benchmark, pricing, and model metadata for 2026.
Choose GPT-5.1 Codex High
- you process long inputs — it offers a 400,000 token context window
Choose Step-3.5-Flash
- you want the strongest raw capability — it leads on 1 of 1 shared benchmarks
- cost matters — it's about 19.6x cheaper per token
- you want the most recent training data — it shipped Feb 2026
- you need open weights you can self-host or fine-tune
At a glance
The differences that matter most.
Performance Benchmarks
Comparative analysis across standard metrics
GPT-5.1 Codex High outperforms in 0 benchmarks, while Step-3.5-Flash is better at 1 benchmark (AIME 2025).
Step-3.5-Flash significantly outperforms across most benchmarks.
Arena Performance
Playground indexes and blind preference scores
Pricing Analysis
Price comparison per million tokens
For input processing, GPT-5.1 Codex High ($1.25/1M tokens) is 12.5x more expensive than Step-3.5-Flash ($0.10/1M tokens).
For output processing, GPT-5.1 Codex High ($10.00/1M tokens) is 25.0x more expensive than Step-3.5-Flash ($0.40/1M tokens).
In conclusion, GPT-5.1 Codex High is more expensive than Step-3.5-Flash.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
GPT-5.1 Codex High accepts 400,000 input tokens compared to Step-3.5-Flash's 65,536 tokens. GPT-5.1 Codex High can generate longer responses up to 128,000 tokens, while Step-3.5-Flash is limited to 8,192 tokens.
Input Capabilities
Supported data types and modalities
GPT-5.1 Codex High supports multimodal inputs, whereas Step-3.5-Flash does not.
GPT-5.1 Codex High can handle both text and other forms of data like images, making it suitable for multimodal applications.
GPT-5.1 Codex High
Step-3.5-Flash
License
Usage and distribution terms
GPT-5.1 Codex High is licensed under a proprietary license, while Step-3.5-Flash uses Apache 2.0.
License differences may affect how you can use these models in commercial or open-source projects.
Proprietary
Closed source
Apache 2.0
Open weights
Release Timeline
When each model was launched
GPT-5.1 Codex High was released on 2025-11-12, while Step-3.5-Flash was released on 2026-02-02.
Step-3.5-Flash is 3 months newer than GPT-5.1 Codex High.
Nov 12, 2025
9 months ago
Feb 2, 2026
6 months ago
2mo newerKnowledge Cutoff
When training data ends
Neither model specifies a knowledge cutoff date.
Unable to compare the recency of their training data.
Provider Availability
GPT-5.1 Codex High is available from OpenAI. Step-3.5-Flash is available from StepFun.
GPT-5.1 Codex High
Step-3.5-Flash
Outputs Comparison
Judge for yourself.
Run your own prompts against GPT-5.1 Codex High and Step-3.5-Flash side-by-side, then vote on the output you prefer.
FAQ
Common questions about GPT-5.1 Codex High vs Step-3.5-Flash.