Hi, it's been possible for a while to build SOF both with Zephyr [1] and with the in-tree XTOS version. We started off by wrapping app calls to OS services into calls to Zephyr. Recently, we've started taking the next steps and started replacing the main code to use native Zephyr interfaces where appropriate, and wrap the calls into XTOS when building with the latter. Intent is to keep both builds functional at all times. Due to the incremental nature, this can be hard to track and understand at times, so I filed today a meta issue to track all ongoing work: - https://github.com/thesofproject/sof/issues/5794 [1] https://thesofproject.github.io/latest/getting_started/build-guide/build-wit... Br, Kai