Some relevant prior work, in case y'all are not aware: T180860, T147696.

It's also worth noting a couple of things our previous methods did not capture:

• mobile-only users will be included in the statistics, even though they do not have the option to switch skins (T180860#6505708)
• this only looks at a user's preference on their "home wiki" (which we defined as the wiki where they had the most edits over the past year, with each Wikidata edit counted as 0.1 rather than 1). This means we don't take into account the global preference for a skin, if one is set (T180860#6256459).

Thanks @nshahquinn-wmf for all the info.

Document some finding in data exploration and some info from the discussion with WEB engineer here.

mediawiki_skin_diff schema captures the skin preference switch events. How to interpret the value in the initial_state and final_state fields in schema :

As of 2022-08-31, the default skin on enwiki is vector legacy. On the pilot wikis, the default skin is Vector(2022).
Pilot wikis are:

• First group of wikis:

Basque Wikipedia
French Wikipedia
French Wiktionary
Hebrew Wikipedia
Persian Wikipedia
Portuguese Wikiversity
Office Wiki

• Second group of wikis :

Bengali Wikipedia
German Wikivoyage
Korean Wikipedia
Portuguese Wikipedia
Serbian Wikipedia
Turkish Wikipedia
Venetian Wikipedia
Wikimedia Incubator

• Third group of wikis :

Moroccan Arabic Wikipedia
French Wikiquote
Indonesian Wikipedia
Portuguese Wikinews
Polish Wikinews
Thai Wikipedia
Vietnamese Wikipedia
Vietnamese Wikibooks
MediaWiki.org (this wiki)
Wikimedia Foundation Governance wiki
Collab wiki
Strategy wiki

• Fourth group of wikis :

Arabic Wikisource
Catalan Wikipedia
Japanese Wikipedia
Polish Wikisource
Chinese Wikinews