Ask HN: Why does Ant, Open AI even need a datacenter?

Others do, see Qwen and other open models. OpenAi and Anthropic's models are a bit larger though, and your computer would run out of memory.

Models, especially the largest, multiple terrabytes of disk and GPU memory.

Example, Kimi 3.1 (open weights), is 3T parameters and requires around $1M worth of hardware to serve the model as provided. Then you'll need electrical upgrades and permission to draw that much power (at home).