Hundreds of Twitter’s remaining employees have resigned ahead of Elon Musk’s “extremely hardcore” cultural reset of the company, according to internal Slack messages seen by The Verge and employee tweets.

The fresh purge of Twitter’s ranks comes after Musk recently fired dozens of employees who criticized or mocked him in tweets and internal messages. Musk then set a deadline of 5PM ET on Thursday for all employees to respond “yes” on a Google form if they want to stay for what he is calling “Twitter 2.0;” otherwise, today would be their final day of work and they would receive a severance package. After the deadline hit, hundreds of employees quickly started posting farewell messages and salute emojis in Twitter’s Slack, announcing that they had said no to Musk’s ultimatum.

“I’m not pressing the button,” one departing employee posted in Slack. “My watch ends with Twitter 1.0. I do not wish to be part of Twitter 2.0.”

Twitter had roughly 2,900 remaining employees before the deadline Thursday, thanks to Musk unceremoniously laying off about half of the 7,500-person workforce when he took over and the resignations that followed. Remaining and departing Twitter employees told The Verge that, given the scale of the resignations this week, they expect the platform to start breaking soon. One said that they’ve watched “legendary engineers” and others they look up to leave one by one.

“It feels like all the people who made this place incredible are leaving,” the Twitter staffer said. “It will be extremely hard for Twitter to recover from here, no matter how hardcore the people who remain try to be.”

Multiple “critical” teams inside Twitter have now either completely or near-completely resigned, said other employees who requested anonymity to speak without Musk’s permission. That includes Twitter’s traffic and front end teams that route engineering requests to the correct backend services. The team that maintains Twitter’s core system libraries that every engineer at the company uses is also gone. “You cannot run Twitter without this team,” a departing employee said.

Several members of Twitter’s “Command Center” team, a group of engineers that is on call 24/7 and acts as the clearing house for problems internally, also tweeted about their departures. “If they go down, there is no one to call when shit breaks,” said a person familiar with how the team operates. The team that manages Twitter API for developers has also been severely gutted.

In a tweet Thursday evening, Musk said: “The best people are staying, so I’m not super worried.”