Comment by jasonpeacock

It's hard to find details...apparently it's code named "red knot" (or "red_knot").

Here's the github issues filter linked in the screenshot:

https://github.com/astral-sh/ruff/labels/red-knot

And the best answer/description of what the type checker will be:

https://github.com/astral-sh/ruff/discussions/15149