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If you keep the traffic split between the variations the same, then there won't be any resampling as you scale up. For example, if you started with 10% of users and a 50/50 split, then want to scale up to 50% of users, still with a 50/50 split, it will work fine as expected. But if you keep the rollout percent the same and change from a 90/10 split to a 50/50 split, then users will be resampled. So bottom line, keep the traffic split the same and just adjust the percent rollout.

Thanks for the response @future-teacher-7046. Next follow up question is what happens when we scale down. For example keep the traffic split between variations same but instead of scaling up from 10% to say 50% , i scaled down from 50% to 10% -> how this would impact the experiment? 1. Will the users be resampled? 2. Or the GB will exclude 40% of users from the experiment and serve those 40% users the default behaviour?

It's #2. If you keep the traffic split the same, it will never do resampling.