The question also puzzles me for long. As far as I knew from staffs in Tobii China, Tobii provide eye trackers to Pico and HTC. But Pico only exposes OpenXR API and hides the access to tobii sdk (as u mentioned) which HTC used to provide. However recently HTC cannot let developers get eye data from tobii eye trackers. Don’t know if they will do the same as Pico.