The closest alternative to GPT-5.6 Luna Pro is GPT-5.6 Luna — comparable intelligence (51.2 vs —); for a cheaper option, GLM 5.2 runs $0.540/M vs $1.00/M; for more speed, Morph V3 Large hits 3.2k t/s; and the best open-weight substitute is GLM 5.2.
GPT-5.6 Luna is the closest alternative to GPT-5.6 Luna Pro, with an Intelligence Index of 51.2 (GPT-5.6 Luna Pro scores —) at $1.00 per million input tokens.
Yes — GLM 5.2 costs $0.540 per million input tokens versus $1.00 for GPT-5.6 Luna Pro, while staying within ~8 points of its Intelligence Index.
GLM 5.2 is the strongest open-weight alternative to GPT-5.6 Luna Pro — downloadable from Hugging Face and self-hostable, scoring 51.1 on intelligence.