SteamVR 2.18.1 quietly changed the driver interfaces third-party add-ons use
SteamVR's 2.18.1 beta changed several of the interfaces third-party drivers build against, and it changed the OSC output that the Steam Link driver exposes. Neither appears in Valve's notes for the beta, and the company set them out only in a reply to an owner whose paid SteamVR add-on had stopped working.
The OSC output Valve changed belongs to the Steam Link driver. Image: Valve
That beta is also the release that added tethered Quest streaming over USB, which is the change most owners went looking for. The interface work reaches a much smaller group: anyone running a community or paid SteamVR driver.
Toggling the OSC output is Valve's first suggestion
SteamVR updated a few interfaces in the latest release, as well as modifying the OSC output that the Steam Link driver exposes. I'd recommend starting with seeing if toggling the OSC output in steam link settings has any affect.
OSC, or Open Sound Control, is the messaging protocol social VR tools use to pass values such as tracker data and avatar parameters between applications, so a change to what the Steam Link driver sends out lands on anything listening for it.
Valve's second pointer is to drivers that hook interfaces to pull data from other drivers directly. That is unsupported, Valve says, and a driver doing it should make sure it is hooking the latest interface versions, because that is what every proprietary SteamVR driver builds against.
One add-on is named, by the owner who lost it
The report describes 2.18.1 breaking the Linux beta of SizeOSC, a paid third-party project that brings Resonite's resize gesture into VRChat, and says it stayed broken after SteamVR was rolled back to the stable build. That owner has passed Valve's explanation to the add-on's developer.
No other add-on has been named, and Valve neither confirmed a bug nor promised a fix. It closed the report on September 25, saying the problem as described was not what was actually going on and that there was too little to work with to help further, while inviting a fresh report if anything else looked wrong with SteamVR.
Aurora and the Steam Link fixes came in the same beta
Valve's notes for 2.18.1 list a new default environment called Aurora, which can be switched off, content-aware colour tinting in the theater environment, gamepad navigation in the System UI, an "Additional Options" menu for lesser-used controls, and a setting to stop games dimming while the dashboard is up. Steam Link gets fixes for video corruption, checkerboarding and stuck streams plus improved automatic bitrate selection, and on Linux async reprojection no longer fails on AMD GPUs.
Valve has been opening up more of the Frame's plumbing this month, including the container that runs Android VR games on the headset. Third-party drivers sit on the other side of that line: they build against interfaces Valve can revise in any release, and 2.18.1 revised them.
Anyone whose SteamVR add-on has stopped working has the OSC toggle to try first, and after that a wait for the add-on's own author to rebuild against the current interfaces. The beta is opt-in, so the stable branch keeps the old interfaces for now.
