Hi, We would like to run experiment on users based on the fact they are new users or existing user at the moment they enter the experiment. I am not sure how to do it. It thought about using an attribute new/existing user but it not be stable for the duration of the experiment since new users will not be new anymore the next day but I want them to remain in the experiment so my windowed metrics can be computed correctly. I wonder if sticky bucket would be a good option to handle that casee. Any advice ?

sticky bucketing would handle this - but you could also use the normal attributes with a bit of custom code and a cookie/local storage to store the state