Having used them heavily for 3D model understanding since February I can say it's nuanced.

Opus 4.6 and 4.7 were bad, but GPT 5.2 and above were very usable. Opus 4.8 was usable, but the GPT 5.x series was better.

Fable is great.

Opus 5.0 was interesting. It could solve some problems that Sol 5.x couldn't solve (applying a G2 curve on a 3 way corner where one face was a Bezier curve) but you had to be super prescriptive ("only answer the question"/"only do what I tell you and stop when done") or it would go on a hugely involved validation journey that didn't really achieve a lot.

Opus 5.5 is better than that was in that respect.

Sol 6.x is great, and my daily driver for this (I use Opus for coding though)

Astra can solve problems that Sol can't but for some reason on easy stuff makes uglier solutions.

For all models it's very interactive though - we aren't at the "agentic design" phase for most things yet.

Here's a sample of what I've been able to get them to design with me: https://x.com/nlothian/status/2099023496794018067