So... here is our small "joke" for the 1st april ;-).
Add the following lines to your Lotus notes.ini
Window_Title="IBM Lotus Notes 9.0 - Internal Beta Version"
And re-start your client. After that you will see this line in the header from your client. After that send our some screenshots to you Lotus Notes friends out there and explain them you have the new Lotus Notes Client :-D.
If you need more infos read the documentation here: