Twitter shares rallied as much as 5% on Monday after the company announced its permanent CEO.

Jack Dorsey, the company's co-founder who had served as interim CEO, was confirmed by Twitter in an SEC filing, following reports last week that he would be filling the role.

After former CEO Dick Costolo (who stepped down from the board Monday) resigned in July, the stock dropped below its IPO price of $26 per share, and fell to a record low. On Friday, it closed up 6% at $26.32.

Amid a slowdown in active user growth and uncertainty over Twitter's leadership, the stock has fallen 27% year-to-date. It's down 51% over the past 12 months.