I am the author of hax, yes.

If you are familiar with pi, then some of the key features listed on the GitHub page (and website) already illustrate substantial differences: hax is much smaller in footprint (I wouldn't even call pi "light-weight", really - heavy js runtime with a lot of dependencies), hax preserves native terminal scrollback (pi uses alt-screen fullscreen, or clears in some cases in differential mode), hax uses normal XDG dirs (pi uses ~/.pi), hax is extended out-of-process (pi suggests in-process plugins).

There are other differences in presentation, and in features (for example, hax has background bash invocation out-of-the-box). Not practical to list all of them.

Thanks I'll have to set aside some time later to try it out. It's kind of a sliding scale, but pi is definitely lighter-weight when compared to harnesses like Opencode and the all-batteries included "Oh-My-Pi".

And of course, “lightweight” does have a lot of interpretations where harnesses are concerned (memory footprint, binary size, performance, system prompt, etc).