Twitter Chief Executive Jack Dorsey announced the departure of multiple department heads on Sunday, marking the biggest management shakeup since he returned to run the social network in mid-2015.

Leaving the company are head of media Katie Jacobs Stanton, product chief Kevin Weil, engineering chief Alex Roetter and human resources leader Brian “Skip” Schipper, Dorsey said in a note posted on Twitter. It’s the latest move in a series of steps Dorsey is taking to overhaul the ailing company, which is struggling to prove its worth to investors. Its stock has fallen nearly 50 percent since Dorsey took over.

Twitter’s success hinges on increasing the number of people who use it and proving it appeals to a mainstream audience as do other social networks such as Facebook and the fast-growing Instagram. Facebook now boasts more than 1.2 billion monthly users and Instagram has 400 million users, butTwitter lags behind with 316 million monthly users (as of July 2015) despite being four years older than the picture-sharing service.

Twitter users are usually staunch advocates of the the social network, but tend to resent changes that are brought in, such as the recent switch from “favoriting” tweets to “liking” them. To grow Twitter, change is inevitable, but Dorsey has to walk the fine line between keeping the current base of users on board and simultaneously introducing new features that will make it appeal to outsiders.

Under the leadership of former CEO Dick Costolo, the platform failed to evolve and draw in these new users. Dorsey is attempting to change this with faster innovation, as with Moments, a company-curated list of the best content on Twitter, and the promise of finding a way to extend tweets beyond the 140-character limit to 10,000 characters.

Chief Operating Officer Adam Bain will temporarily take responsibility for the media and HR teams, with Chief Technical Officer Adam Messinger taking over engineering and product design for now, Dorsey said. He is also expected to bring in two new board members as early as this week, the Wall Street Journal reports, citing people familiar with the matter.

It seems that despite the abrupt Sunday night announcement of the changes, the departing staff are leaving on good terms.
Stanton posted on Medium about her time on Twitter and explained that she was resigning “because it’s time for me to pour more of my energy into my family.” Roetter posted a series of three tweets saying he had been “thinking about this for a while.” Weil kept it short and sweet, saying “next up” were his wife, son and “some long runs,” signing off with “GO TEAM!” Schipper eschewed Twitter altogether.