NVIDIA Nemotron 3 Ultra: 550B resets the US open-weights bar

NVIDIA released Nemotron 3 Ultra on June 1, a 550B-parameter open-source model. The model is the first US open-source 550B-class model, taking the top spot on several open-weight intelligence leaderboards. The release signals that the US open-source ecosystem is competitive with the closed-source frontier, with NVIDIA as a major contributor.