NVIDIA shipped Nemotron 3 Ultra on June 4, 2026 — its largest open-weights model and the new high-water mark for US open releases. Before you wire it into an agent harness, here is exactly what landed and where it sits on the leaderboard.

What NVIDIA Launched on June 4: Specs and Leaderboard Position

Nemotron 3 Ultra is a 550-billion-parameter hybrid Mamba-Transformer mixture-of-experts (MoE) model with up to roughly 55B active parameters per token — about 90% sparsity — released by NVIDIA on June 4, 2026 . It tops the three-model Nemotron 3 family (Nano, Super, Ultra), ships a 1M-token context window, and uses NVFP4 (4-bit floating point) training on NVIDIA's Blackwell architecture plus a "LatentMoE" hardware-aware expert router . It is post-trained for agent harnesses including Hermes Agent, LangChain Deep Agents, OpenHands, and OpenCode .

On the Artificial Analysis Intelligence Index, Ultra scored 48 — the most capable open model from a US lab to date — but it trails the Chinese-led Kimi K2.6 and closed models such as Anthropic's Opus 4.8 :

Model