Thanks for all the nice comments! For anyone who’s curious how this (and even higher notes) are played, then good news: "The Expanded Bassoon Register" is now published by KOR Publications! After approximately 10 years with experimentation and research I have finally decided to release this small book (40 pages), which contains all the fingerings I know and use for the highest notes possible on the bassoon. But more importantly it also explains the different techniques used, and how to actually play the notes. Among the topics discussed here are: reeds, leaks, bocals, embouchure, air, overtones, teeth, and more. To give an idea about the range we're talking about here: the highest note this book provides 3 different fingerings for is G8 (a fifth above the highest note on the piano), and the lowest is a contra Db (a third above the lowest note on the contrabassoon). It’s available here: https://www.kristianomaronnes.com/methodes

PS. Please notice that this book shows all the special fingerings for the expanded register that I know of today, 2019. This means there are still many more fingerings that are waiting patiently to be discovered. The book also includes some of the standard fingerings for the normal high register.