Over the last several years, the Growth features have been deployed to 80% of new accounts (the treatment group) and have been withheld from 20% of new accounts (the control group). Keeping a control group enables us to analyze large experiments on the overall impact of the Growth features, but the downsides are (a) the valuable features are withheld from a fifth of newcomers, and (b) when some newcomers don't have the features it causes confusion for campaigns and events and for on-wiki discussion.
In {T270786}, we completed a second round of analysis using this large experiment, and we now feel like we have sufficiently experimented with the overall impact of the Growth features. We want to remove the control groups for most Wikipedias, and in the future, experiment //within// the Growth features.
Specifically, all Wikipedias except the following should give Growth features to 100% of new accounts going forward. These Wikipedias should continue to have the control groups they currently have with no changes:
* Arabic
* Czech
* Bengali
* Spanish
* Portuguese
* Turkish
* Persian
* German
* English