I'm merging the elite and spartan into one bone set.
Sapien tells me that the biped's model does not match the animation graph, even though the checksums are the same.
There are a lot of bones in the biped, and the model tag lists them all. In the animation tag, only half of the bones are listed.

GBXModel tag says:
NODES: bip01 pelvis, bip01 l thigh, bip01 pelvisz, bip01 r thigh, bip01 spine, bip01 l thighz, bip01 r calf, bip01 r thighz, bip01 spine1, bip01 spinez, bip01 l calfz, bip01 l clavicle, bip01 l foot, bip01 neck, bip01 r calfz, ... etc ... there are a lot ... frame mandible lower rightz, frame mandible upper leftz.

MODEL_Animations says:
NODES: bip01 pelvis, bip01 l thigh, bip01 r thigh, bip01 spine, etc. All the default ones, none of the elite bones.

What's going on? Is there a certain sceme that I HAVE to follow for bone names, or is there a limit on bones or something?

That's not it... all those bones are in there.
It's the spartan bones and elite bones joined at bip01 pelvis. En elite geometry is rigged to the elite bones, and a spartan is rigged to the spartan bones.

If there are ones with matching names, name them different...
If they have different names, make them match...
Idk rly. Just throwin ideas out there.

Too many bones maybe?
I wonder if there's a bone limit.

Is the elite pelvis linked to the spartan pelvis?
Halo might have a problem with having a pelvis linked to a pelvis. Not sure, but I know Halo can be pretty picky about a lot of stuff.

Does halo require biped bones to have body-part names, like pelvis and clavicle? I've noticed that the elite mandibles are frames, and not bip01s.
Perhaps I should remove the bip01 prefix from all the elite bones. This doesn't explain how the mandibles are missing from the animation graph now, however.
People with biped experience need to read this.