According to one possibly over-simplistic measure, the core Wikimedia community, and in particular the core community on the English Wikipedia, has recently stopped declining and might even have started to grow again.
Editors saving more than 100 edits per month on the English Wikipedia
Editors saving more than 100 edits per month on all Wikipedia languages
For some years now the English Wikipedia and the Wikimedia movement generally have been losing active editors faster than they have been recruiting them.
But one interesting indicator has now started to climb and indicates that the core community may actually be growing again. Though a range of other indicators from the appointment of new admins on the English wikipedia, the number of new accounts created, and the number of editors doing more than five edits per month are still flat or in decline.
The number of editors saving more than 100 edits each month is a long-standing metric published about Wikipedia and other WMF projects. For seven consecutive months, from January to July 2015, that indicator has been positive on both the English Wikipedia community and the whole Wikimedia project—though the situation is more complex on some other sites, such as the German Wikipedia.
We know there are seasonal events that affect the community, and months themselves vary in length, so February 2015 was shorter than January or March; but more editors were contributing more than 100 edits that month than in February 2014; similarly, in January 2015 there were more active editors than in January 2014, a trend that has now run for seven months. Last month, 12,349 editors made more than 100 edits across all projects, 10,280 editors across all versions of Wikipedia, and 3,399 editors on the English Wikipedia, as opposed to 11,257, 9,420, and 3,024 editors respectively in July 2014.
The matter has been discussed on the research mailing list, Wiki-research-l, during the past two weeks.
As with any data over time, there is always the risk that this could just be anomalous, but Wikimedia Foundation data analyst Erik Zachte has now said of the phenomenon: "The growth seems real to me." Zachte has also pointed to the late 2014 speed-up of editing on the Wikimedia sites as a potential contributor to the increase. Implementing HHVM speeded up the saving of edits, which should logically have more impact on wiki gnomes doing lots of small edits than on editors who make just a few saves per hour.
Another theory suggested on the research list and elsewhere has attributed the increase to the improvements to Visual Editor, though with barely ten percent of the most active editors on English Wikipedia using it, it is unlikely to be a major or sole reason for the apparent increase.
The different leadership style of new Foundation executive director Lila Tretikov may be bearing fruit, in terms of better relations between the Foundation and the most active editors.
There is also some concern that Editors saving over 100 edits per month is a simplistic metric; for example, it will include users of highly automated tools such as AutoWikiBrowser, STiki, or Huggle who may achieve that edit count in less than an hour per month, but omits an editor who spends an evening every week writing or rewriting one or two articles, but who might only save an edit every half an hour in that evening.
Should the trend continue, and assuming that someone doesn't find a software bug that has caused the anomaly, future lines of analysis could include examining how much of the increase is due to fewer editors leaving, more inactive editors returning, more new editors joining, and a greater number of casual editors increasing their editing frequency to more than 100 edits per month.
August figures are expected in about a month. It will be very interesting to see whether the trend continues.