Twitter CEO Dick Costolo to resign, 140-character limit lifted for direct messages

The company announced (PDF link) to investors that Costolo will step down effective July 1, with co-founder and chairman Jack Dorsey to serve as interim CEO while Twitter's board searches for a suitable replacement.

"I am tremendously proud of the Twitter team and all that the team has accomplished together during my six years with the Company," Costolo said. "We have great leaders who work well together and a clear strategy that informs our objectives and priorities."

Twitter has a tumultuous history when it comes to upper management. Dorsey, who led the company through investment rounds, was pushed out and replaced by co-founder Evan Williams in 2008. Three years later, Dorsey returned as executive chairman after Williams was ousted, to be succeeded by Costolo.

Early investor Chris Sacca recently published an analysis of how Twitter can change for the better, which put even greater pressure on Costolo and his team, reports The New York Times.

Costolo will remain on Twitter's board directly following his transition out. Along with interim CEO duties, Dorsey plans to serve the same role at his payments firm Square.

Earlier in the day, Twitter announced an upcoming change to the DM character cap as part of a larger effort to bolster supporting and complementary offerings.

The direct messaging feature was most recently updated in April with open DMs, or the ability to send messages to other users, followed or not.

Twitter did not specify a date for lengthier DM support, saying only to expect the change sometime in July.