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GPT-5 Codex vs Step-3.5-Flash

GPT-5 Codex significantly outperforms across most benchmarks.

OpenAI · StepFun · Updated for 2026

Which is better?

GPT-5 Codex outperforms in 1 benchmarks (SWE-Bench Verified), while Step-3.5-Flash is better at 0 benchmarks. GPT-5 Codex significantly outperforms across most benchmarks.

Based on current benchmark, pricing, and model metadata for 2026.

Choose GPT-5 Codex

  • you want the strongest raw capability — it leads on 1 of 1 shared benchmarks

Choose Step-3.5-Flash

  • 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.

GPT-5 Codex
OpenAI
Step-3.5-Flash
StepFun
Benchmark wins
1 of 1
0 of 1
Input price
— / M
$0.10 / M
Output price
— / M
$0.40 / M
Context window
—
65,536
Released
Sep 2025
Feb 2026
License
Proprietary
Apache 2.0

Performance Benchmarks

Comparative analysis across standard metrics

1 benchmarks

GPT-5 Codex outperforms in 1 benchmarks (SWE-Bench Verified), while Step-3.5-Flash is better at 0 benchmarks.

GPT-5 Codex significantly outperforms across most benchmarks.

Tue Aug 25 2026 • llm-stats.com

Arena Performance

Playground indexes and blind preference scores

Context Window

Maximum input and output token capacity

Only Step-3.5-Flash specifies input context (65,536 tokens). Only Step-3.5-Flash specifies output context (8,192 tokens).

OpenAI
GPT-5 Codex
Input- tokens
Output- tokens
StepFun
Step-3.5-Flash
Input65,536 tokens
Output8,192 tokens
Tue Aug 25 2026 • llm-stats.com

License

Usage and distribution terms

GPT-5 Codex 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.

GPT-5 Codex

Proprietary

Closed source

Step-3.5-Flash

Apache 2.0

Open weights

Release Timeline

When each model was launched

GPT-5 Codex was released on 2025-09-15, while Step-3.5-Flash was released on 2026-02-02.

Step-3.5-Flash is 5 months newer than GPT-5 Codex.

GPT-5 Codex

Sep 15, 2025

11 months ago

Step-3.5-Flash

Feb 2, 2026

6 months ago

4mo newer

Knowledge Cutoff

When training data ends

GPT-5 Codex has a documented knowledge cutoff of 2024-09-30, while Step-3.5-Flash's cutoff date is not specified.

We can confirm GPT-5 Codex's training data extends to 2024-09-30, but cannot make a direct comparison without Step-3.5-Flash's cutoff date.

GPT-5 Codex

Sep 2024

Step-3.5-Flash

—

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Judge for yourself.

Run your own prompts against GPT-5 Codex and Step-3.5-Flash side-by-side, then vote on the output you prefer.

GPT-5 Codex
✓ Preferred
Step-3.5-Flash
Open in Playground

FAQ

Common questions about GPT-5 Codex vs Step-3.5-Flash.

Which is better, GPT-5 Codex or Step-3.5-Flash?

GPT-5 Codex significantly outperforms across most benchmarks. GPT-5 Codex is made by OpenAI and Step-3.5-Flash is made by StepFun. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.

How does GPT-5 Codex compare to Step-3.5-Flash in benchmarks?

GPT-5 Codex scores SWE-Bench Verified: 74.5%. Step-3.5-Flash scores AIME 2025: 97.3%, Tau-bench: 88.2%, LiveCodeBench v6: 86.4%, IMO-AnswerBench: 85.4%, SWE-Bench Verified: 74.4%.

What are the context window sizes for GPT-5 Codex and Step-3.5-Flash?

GPT-5 Codex supports an unknown number of tokens and Step-3.5-Flash supports 66K tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between GPT-5 Codex and Step-3.5-Flash?

Key differences include licensing (Proprietary vs Apache 2.0). See the full comparison above for benchmark-by-benchmark results.

Who makes GPT-5 Codex and Step-3.5-Flash?

GPT-5 Codex is developed by OpenAI and Step-3.5-Flash is developed by StepFun.

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