K2 Horizon 375B-A23B

Institute of Foundation Models · open weight · k2-horizon-375b-a23b

K2 Horizon 375B-A23B is the flagship of the Institute of Foundation Models' (MBZUAI) fully open K2 Horizon family: a sparse Mixture-of-Experts reasoning model with 375B total and 23B active parameters per token (61 layers, 192 routed experts with 8 active plus 1 shared expert, 250K vocabulary). It was pretrained on about 15.1T tokens in two phases, context-extended to a native 524,288-token (512K) window during midtraining, and post-trained by merging RL experts for knowledge work, instruction following, search, tool use, and reasoning. Text in, text out, with per-request reasoning effort (high recommended) and JSON/XML tool-call formats. It targets agentic tool use, terminal, coding, and long-horizon workflow tasks. Released 2026-09-03 under Apache 2.0 with BF16 weights plus FP8 and NVFP4 builds, intermediate checkpoints, training data, code, and logs. IFM lists Compass, Cerebras, and Nebius as API inference partners; no priced provider is cataloged yet.