Ai2's HiRO-ACEv2 emulates 3 km extreme weather at about 1/300th of the original's cost

Serguey Asael Shinder15 October 2026, 06:372 min read

Ai2 published HiRO-ACEv2 on 14 October 2026, an update to its High Resolution Output Ai2 Climate Emulator. According to the announcement, the full system generates global 3 km climate data at roughly 1/300th the cost of X-SHiELD, a high-resolution global atmospheric model that explicitly simulates storms.

How the system is built. HiRO-ACE, introduced earlier in 2026, has two parts: ACE, an AI model that runs at a coarse 100 km resolution, and HiRO, which sharpens those outputs into 3 km detail. The main change in v2 is the new downscaler, HiROv2, which predicts several high-resolution fields at once instead of only rainfall, and was trained with changes aimed at extreme events.

What Ai2 reports. Given coarsened X-SHiELD data, HiROv2 matches the target simulation's high-resolution statistics to within 3%, including events that occur once in a million data points. It estimates the total energy of tropical cyclones, including storms it did not see in training, and generates hurricanes with realistic eyes and rain bands — though Ai2 notes that winds and pressure around the eye remain more lopsided than in X-SHiELD. An updated ACE, run over 10 years, produces hurricanes, average climate patterns and distributions of rain, wind and pressure that line up with X-SHiELD; combining the two, Ai2 generated a full year of global 3 km data whose statistics closely match the original model.

Cost. Global high-resolution output costs about 300 times less than running X-SHiELD; for a single region, the savings can be more than a hundred times greater, depending on its size. A streamlined HiROv2 that could be more than ten times faster is in the works.

Limits named by the team. Because HiRO learned from X-SHiELD, it only works with the version of ACE tuned to match it, so it cannot yet produce high-resolution data for other climates — a warmer future, or the historical record in datasets such as ERA5. Planned next steps are training on new X-SHiELD runs, including one simulating a world 4 °C warmer, and adding outputs such as near-surface temperature and snow and ice.

The models are available to download, with tutorial notebooks and a web demo comparing HiROv1, HiROv2 and X-SHiELD output side by side.

Source: Ai2 on Hugging Face, "HiRO-ACEv2: Simulating extreme weather at 3 km resolution for a fraction of the cost" — https://huggingface.co/blog/allenai/hiro-acev2