StepFun Step 3.5 Flash vs Codex (OpenAI)
Which one should you pick? Here's the full breakdown.
StepFun Step 3.5 Flash
StepFun's (China) agent-focused open-weight model -- Step 3.5 Flash launched 2026-02-01. 196B sparse MoE, ~11B active. Benchmarks slightly ahead of DeepSeek V3.2 at over 3x smaller total size. Step 3 (321B / 38B active, Apache 2.0) and Step3-VL-10B multimodal also in the family
Codex (OpenAI)
OpenAI's cloud-based coding agent -- runs parallel tasks, proposes PRs, and lives inside ChatGPT
Powered by GPT-5.3-Codex / GPT-5.4
| Category | StepFun Step 3.5 Flash | Codex (OpenAI) |
|---|---|---|
| Ease of Use | 6.0 | 8.0 |
| Output Quality | 8.0 | 8.0 |
| Value | 9.0 | 8.0 |
| Features | 8.0 | 9.0 |
| Overall | 7.8 | 8.3 |
Pricing Comparison
| Feature | StepFun Step 3.5 Flash | Codex (OpenAI) |
|---|---|---|
| Free Tier | Yes | Yes |
| Starting Price | $0 | $0 |
Benchmark Head-to-Head
GPT-5.3-Codex benchmarks — StepFun Step 3.5 Flash has no published benchmarks
| Benchmark | Description | Score |
|---|---|---|
| SWE-bench | Real GitHub issue fixing | 72% |
| HumanEval | Python code generation | 95% |
Which Should You Pick?
Pick StepFun Step 3.5 Flash if...
- ✓Better value for money (9/10)
Teams building agent systems on Chinese open-weight foundations who want something other than DeepSeek or Qwen, especially if agentic tool-use is the primary workload. Also good for Chinese-market products where StepFun's domestic tuning advantages matter. And for anyone looking to add diversity to their open-weight evaluation matrix beyond the top-3 Chinese labs.
Visit StepFun Step 3.5 FlashPick Codex (OpenAI) if...
- ✓Easier to use (8 vs 6)
- ✓More features (9 vs 8)
Developers already paying for ChatGPT Plus who want a coding agent at no extra cost. Especially good for parallel task execution -- assign multiple bug fixes or feature branches and let Codex work them simultaneously.
Visit Codex (OpenAI)Our Verdict
Codex (OpenAI) edges out StepFun Step 3.5 Flash with a 8.3 vs 7.8 overall score. Both are solid picks, but Codex (OpenAI) has the advantage in features.