The closest alternative to Claude Sonnet 4.6 is Step 3.7 Flash — comparable intelligence (42.6 vs 42.6); for a cheaper option, GPT-5.4 runs $2.50/M vs $3.00/M; for more speed, GLM 4.7 hits 478 t/s; and the best open-weight substitute is MiniMax M3.
Step 3.7 Flash is the closest alternative to Claude Sonnet 4.6, with an Intelligence Index of 42.6 (Claude Sonnet 4.6 scores 42.6) at $0.200 per million input tokens.
Yes — GPT-5.4 costs $2.50 per million input tokens versus $3.00 for Claude Sonnet 4.6, while staying within ~8 points of its Intelligence Index.
MiniMax M3 is the strongest open-weight alternative to Claude Sonnet 4.6 — downloadable from Hugging Face and self-hostable, scoring 54.7 on intelligence.