According to Entertainment Weekly, the Star Wars 8 has begun filming. The info comes from Disney CEO Bob Iger during a Disney quarterly earnings call where he revealed Star Wars: The Force Awakens "earned more than $3 billion globally in consumer products" on top of the $2 billion in box office returns. Considering all of Lucasfilm was sold for "only" $4 billion, by the time Awakens adds home video sales and TV rights to the mix, Disney basically recouped its purchase cost on the first film alone.
“There is no better way to propel this franchise into the future than producing quality products,” [Iger] said. “Filming of Star Wars: Episode VIII, the next chapter of the legendary saga, has just commenced and it will be in theaters December 2017. And production of Episode IX, a 2019 release, has also begun. ...Filming of Rogue One is virtually completed and we absolutely love what we’ve seen so far."
In regards to Episode IX, he probably means pre-production as in script writing, working on set designs, costumes, casting, CGI models and so forth that will probably take a minimum of six months to complete. Production (as in principle photography) will likely not start on that film until late 2017 to early 2018.