Been diving into APEX, however, most of my rigging tends to be quadruped rigging and I've hit a bit of a wall.

Haven't had as much time as I would like to expllre, but some cursory experiments seem to show that currently neither the auto-rig components nor the APEX IK solvers can handle 3-bone IK. Anyone found any way to do quadruped rigging with the current APEX nodes?

Or have suggestions about how to build a spring solver from scratch? I'd be willing to put the time in to crafting it from scratch if I understood the underlying math better. Any help would be appreciated.

That is indeed still missing, please make sure to log an RFE for that (ie. Support > Report a Bug/RFE) in the menu above on this website.

Wouldn't the chicken from the Lucha and Chicken scene be a good example of a 3-bone IK? I mean I don't really know, so I'm also asking. But looking at the scene, there it is. Or am I missing something important here?

I don't see a 3-bone IK in Chicken. I've only found a spline rig, which is different from 3-bone IK. Perhaps I missed something tho.

Actually you can do 3-bone (or 4, or any) IK with FBIK... of course it's painful to use just like other APEX nodes.

From what I can tell from the Chicken rig, Walter is using a basic 2-bone IK to drive the hip-knee-ankle portion of the leg and then driving the ankle_ctrl with a parenting / lookat setup based on the ball_ctrl. So the ball_ctrl drives the ankle_ctrl, which is the target of a basic 2-bone IK.

Like a lot of things in the APEX beta, it will work, but it's a bit of a workaround. There are other rigging set-ups that require 3-bone spring IK setups that are more elegant and produce more natural results. Which is why I was asking, but thanks for the responses. Looking forward to future releases.