Is Zero-K Pro HUD Overlay Suite free?

Yes. Zero-K Pro HUD Overlay Suite is released under GPL-2.0-or-later and costs nothing. Neither it nor Zero-K has any paid content.

What do I need to run Zero-K Pro HUD Overlay Suite?

Zero-K, which is itself free. Zero-K Pro HUD Overlay Suite is an add-on and will not run standalone.

The PlayBound Launcher installs it in one click from Zero-K's mods list. You can also install it by hand — full steps are on this page.

Roughly 5 MB, on top of the base Zero-K installation.

Yes. The source is published at github.com/ZeroK-RTS/Zero-K under GPL-2.0-or-later.

Zero-K Pro HUD Overlay Suite — Free Zero-K Mod · PlayBound