The closest alternative to GPT-5.1-Codex is Claude Opus 4.5 — comparable intelligence (43.1 vs 43.1); 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.
Claude Opus 4.5 is the closest alternative to GPT-5.1-Codex, with an Intelligence Index of 43.1 (GPT-5.1-Codex scores 43.1) at $5.00 per million input tokens.
Yes — MiniMax M3 costs $0.300 per million input tokens versus $1.25 for GPT-5.1-Codex, while staying within ~8 points of its Intelligence Index.
MiniMax M3 is the strongest open-weight alternative to GPT-5.1-Codex — downloadable from Hugging Face and self-hostable, scoring 54.7 on intelligence.