Houdini Upgrade Guides
Upgrading Houdini From USD 20.08 to 21.02, describing the work required to upgrade Houdini's USD library
Upgrading Houdini From USD 21.02 to 21.05, the adventure continues
Upgrading Houdini From USD 21.05 to 21.08, tl;dr: a zero-effort upgrade
License: CC BY 4.0, Copyright Contributors to the ASWF USD working group.