NOTE

Hypercollider's impact is unlikely to be noticed in standard gameplay.
It is optimizing for a relatively niche case, that only happens in modded games, and even then is relatively uncommon.

Lithium compat

Lithium is incompatible with hypercollider under default configs.
However, the hypercollider configuration file comes with comments on what to do to make them work with eachother.

I do recommend using lithium with hypercollider.

Client-sided?

Hypercollider makes optimizations to both server and client side logic. I have not tested hypercollider on a vanilla/actual server, so I do not know how anticheats will respond to it.
Here be dragons; an anticheat may be able to flag it.

About

Hypercollider is a mod designed specifically to optimize Minecraft's collision logic
It may change behavior, but for the most part it shouldn't be noticeable

Hypercollider is meant to optimize for large scale entities, such as a 64x scale player with pehkui
Funnily enough, achievements are a massive part of player collision lag, so I actually had to optimize some achievement logic in order to get the game to perform well.

Hypercollider is still early in development, and I know I still have stuff to optimize.

Performance Graphs

The screenshots below are for a 64x scale player.

The reason I'm not including lithium on its own, is because it seems to have done so little on its own that I'm not even actually confident I had it installed.