Nemotron 3 Ultra: Build a 550B Tool-Use Agent

On June 4, NVIDIA dropped Nemotron 3 Ultra, a 550-billion-parameter Mixture-of-Experts model with only 55B active parameters per token, released fully open: weights, training data, and recipes, under the permissive OpenMDW-1.1 license. It is not a chatbot that happens to do tools. It was post-trained specifically for the thing most teams are struggling with right now: long-running agents that plan, call tools, read observations, delegate, and recover from errors across dozens of turns without losing the plot.