Sacks reports GPT 5.5 is built on SPUD, OpenAI's first new base model in over a year.
“GPT 5.5 is based on a new base model called SPUD, which is the first base model upgrade they've done in, I don't know, over a year.”
“Harvey is a great example of how American companies are building world-class specialized models: they took an open-source base (Kimi K3), post-trained it on legal data, and delivered state-of-the-art performance on legal benchmarks at a fraction of the cost of frontier models. https://t.co/YO2tE0O11f”