While some spec sheets have listed the JetStream as running Android 9, it's never been actually available for me. This morning the update was available. I'm not sure what exactly is new for Android TV but at least this finally puts the device on par with the Mi Box S.
Edit: YouTube 4K HDR works, but I have no idea if that was already the case in Android 8.
You came late to the party, anyway welcome and have fun!:
https://www.reddit.com/r/AndroidTV/comments/h8cijr/i_finally_received_the_android_9_pie_on_the/?utm_source=share&utm_medium=web2x
Even though it has the same specs as the Mi Box S, it has proven better regarding the stability of the OS compared to the Mi Box when Android 9 arrived.
Mi Box fanboys can't stand the fact that Xiaomi devs are pretty bad at fixing bugs, I owned a Mi Box S and I sold it just to get the Jetstream, it's the best investment I've made ever since I bought the original Mi Box.