Constraints

All six VRChat constraint types become their Basis equivalents: position, rotation, aim, parent, scale and look-at. VRM has three of its own, which are covered on the VRM page.

Basis also ships its own converter for Unity's built-in constraints and Animation Rigging, which this does not duplicate. If your avatar uses those instead, use BasisConstraintConversion from the Basis SDK.

What carries across

Sources with their weights and offsets, the rest pose, per-axis freezing, the world up mode and its reference object, and the active state.

A VRChat constraint can drive a transform other than the one it sits on. Basis constraints, like Unity's, always drive their own object, so the constraint is written onto the transform it drives.

What does not

Solve In Local Space, Freeze To World and Rebake Offsets When Unfrozen have no equivalent anywhere in Basis, and are reported when they were set.