Microsoft AI finishes pre-training MAI-Base-2, a 2.8T-parameter model

Microsoft AI has finished pre-training MAI-Base-2, a mixture-of-experts model with 2.8T parameters, 80B of them active per token. Its predecessor, MAI-Base-1, has 1T parameters with 35B active and underlies MAI-Thinking-1, which the lab announced in June 2026. A base model is the raw result of pre-training, before the post-training that shapes it into a usable assistant.

The lab tested it on held-out code, question answering, STEM and maths sets kept out of its training data, scoring bits per byte, where lower is better. MAI-Base-2 beat DeepSeek-V4-Pro-Base, the strongest open base model, and three post-trained open models, a comparison the lab says post-training may affect.

It also estimates that DeepSeek-V4-Pro-Base used 4.2 to 12.3 times the training compute that its own recipe would need for the same scores.

Training ran on 16k GB200 GPUs for 38 days in August and September 2026, on a 50T-token mixture with a March 2026 knowledge cutoff. The lab says it used no distillation from other models, and unlike its predecessor, MAI-Base-2 learned from images from the start.

Microsoft AI plans to use the model first in Microsoft’s own products and to license the weights to trusted partners through Foundry. It hasn’t given a release date or price.