Huawei has recently said that their smartphones running EMUI 5.0 would not be updated to 5.1. However, XDA Senior Member was able to get their hands on Mate 9 software running EMUI 5.1 on the Huawei Mate 9. They said the software seems stable and is very similar to P10’s firmware at this point. They even noticed this early build of the Chinese version includes Google Play Services out of the box, surprisingly.
Photo Shows EMUI 5.1 on the Huawei Mate 9