I recently used Opus 5.5 to diagnose and discover a certain (niche) cleartext format CAD file. Also for generating small, new CAD files containing a small model for test purposes. All with satisfaction.

Coincidentally, I also seen a (private) demo using GPT-6 Astra designing wall panel joints based on some pre-determined rules, 2D lines specifying the layout, and later altering the design following a hand sketch (photo of a sketch). That looked promising too. It was claimed that spatial reasoning of Astra is elevated, can work well with 3D models and formats.

None of those are production (something to manufacture) level just yet. But if I had time I'd explore this manipulating CAD files by an agent route, opening those files in the usual tools I have at my disposal.

Talking/chatting about 3D is like dancing about architecture in my view, so I think this LLM use route is not sustainable straight, still, my above casual encounters suggest, for simple things, combined with manual adjustments, it may be alright.