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.
And of course, “lightweight” does have a lot of interpretations where harnesses are concerned (memory footprint, binary size, performance, system prompt, etc).
Some feedback but it might be worth calling out how your harness differs from other relatively light-weight ones like Pi. I assume its got a much smaller memory footprint given yours is C versus Pi's. There are so many agentic harnesses out there that a comparison table might be a nice thing to have on the landind page.
Note: Just to be clear, I'm not accusing you of trying to hide it, given that the GitHub account for Hax is basically identical to your HN account.