The closest alternative to GPT-5.1 is Nemotron 3 Ultra (free) — comparable intelligence (47.7 vs 47.7); for a cheaper option, MiniMax M3 runs $0.300/M vs $1.25/M; for more speed, GLM 4.7 hits 427 t/s; and the best open-weight substitute is MiniMax M3.
Nemotron 3 Ultra (free) is the closest alternative to GPT-5.1, with an Intelligence Index of 47.7 (GPT-5.1 scores 47.7) at Free per million input tokens.
Yes — MiniMax M3 costs $0.300 per million input tokens versus $1.25 for GPT-5.1, while staying within ~8 points of its Intelligence Index.
MiniMax M3 is the strongest open-weight alternative to GPT-5.1 — downloadable from Hugging Face and self-hostable, scoring 54.7 on intelligence.