NVIDIA: Nemotron 3 Ultra

An open 550B-parameter hybrid Mamba-Transformer MoE (55B active, 1M context). The interesting part is the OpenMDW 1.1 license: full weights plus synthetic data plus training recipes. It's the strongest US open-weights model, and it still trails Kimi K2.6 by ~6 points on the Artificial Analysis Intelligence Index.

Sources: NVIDIA blog, Linux Foundation (OpenMDW)