StepFun Step 3.5 Flash vs Codex (OpenAI)

Codex (OpenAI) edges out StepFun Step 3.5 Flash by 0.5 points (8.3 vs 7.8) -- a A-tier vs B-tier split that's narrow but real. Not a blowout; both belong on a shortlist. The score gap shows up most clearly in the categories that matter for Codex (OpenAI)'s strengths, so if those categories are your priority, the lead translates.

Pricing-wise, both tools have a free tier (StepFun Step 3.5 Flash starts $0, Codex (OpenAI) starts $0), so you can test either without committing. Compare what each free tier actually unlocks -- usage caps, model access, and feature gates differ a lot more than the headline price suggests, especially as both vendors have tightened limits in 2026.

By use case: pick StepFun Step 3.5 Flash when 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. Pick Codex (OpenAI) when developers already paying for chatgpt plus who want a coding agent at no extra cost. The two tools aren't fighting for the same person -- they're aiming at adjacent jobs that occasionally overlap. If you're squarely in Codex (OpenAI)'s lane, the tier-list ranking and the use-case fit point the same direction; if you're in StepFun Step 3.5 Flash's lane, the score gap matters less than the fit.

Bottom line: Codex (OpenAI) is the safer default for most readers, but StepFun Step 3.5 Flash is competitive enough that the tie-breaker is your specific workload, not the spec sheet.