The closest alternative to Step 3.5 Flash is Kimi K2.5 — comparable intelligence (37.3 vs 37.8); for a cheaper option, Nemotron 3 Ultra (free) runs Free/M vs $0.090/M; for more speed, gpt-oss-120b (free) hits 554 t/s; and the best open-weight substitute is MiniMax M3.
Kimi K2.5 is the closest alternative to Step 3.5 Flash, with an Intelligence Index of 37.3 (Step 3.5 Flash scores 37.8) at $0.375 per million input tokens.
Yes — Nemotron 3 Ultra (free) costs Free per million input tokens versus $0.090 for Step 3.5 Flash, while staying within ~8 points of its Intelligence Index.
MiniMax M3 is the strongest open-weight alternative to Step 3.5 Flash — downloadable from Hugging Face and self-hostable, scoring 54.7 on intelligence.