Interesting. This is the first I've heard of Zuban.
The fact that Mypy fails so badly matches my experience. It would be interesting to see exactly where Pyright "fails". It's been so reliable to me I wouldn't be 100% surprised if these are deliberate deviations from the spec, where it is dumb.
Pyright had 100% conformance until recently. There was a new PEP that was accepted which required some new conformance tests, which no type checker has added support for yet.
I think Zuban's license limited its exposure. I knew about Zuban but didn't pay attention to it. A proprietary development dependency was a no-go for my FLOSS projects, and I didn't want to adopt a separate tool just for proprietary code.
I see that Zuban went AGPL in September 2025 (with exceptions available). This makes it a lot more interesting.
The fact that Mypy fails so badly matches my experience. It would be interesting to see exactly where Pyright "fails". It's been so reliable to me I wouldn't be 100% surprised if these are deliberate deviations from the spec, where it is dumb.