Elon Musk has given Twitter staff an ultimatum over their future at the social media platform, telling them to commit to an “extremely hardcore” working culture of long hours or receive three months of severance.

In an email to staff, Musk told employees “we will need to be extremely hardcore” to build what he referred to as Twitter 2.0. “Only exceptional performance will constitute a passing grade,” he added.

Employees have been asked to formally register their desire to be part of the new Twitter through a link in the email. Those who have not done so by 5pm EST on Thursday will receive three months of severance pay, according to the email seen by the Financial Times and first reported by the Washington Post.

The email comes less than two weeks after Musk axed about half of Twitter’s 7,500-strong workforce following his $44bn takeover at the end of last month. This week, more staff were fired and locked out of systems, some after expressing concerns or dissent publicly on Twitter or through internal messages on Slack, according to three former employees.

It is the latest development in a tumultuous few weeks for Twitter under Musk’s helm, following a botched rollout of the flagship premium subscription service Twitter Blue, which saw its “blue tick” feature abused by impersonators on the platform.

It also suffered an exodus of some remaining top executives last week, adding to concerns from regulators about its data security and compliance with privacy rules.

During court proceedings in Delaware on Wednesday related to a dispute over his multibillion-dollar Tesla pay deal, Musk said that he was spending lots of his time at Twitter “post-acquisition to reorganise the company” but that he planned to “find someone else to run Twitter, over time”.

He also admitted bringing in nearly 50 Tesla engineers to help with the restructuring, on a voluntary basis after-hours, but that this was over and no Tesla board members had objected to it.

“The fundamental organisational restructuring will be done by the end of this week,” he added.

Musk revealed in a tweet on Tuesday that Twitter Blue, the platform’s subscription offering that enables paid users to access additional features including a blue tick, would return on November 29 after its high-profile glitches.

Blue tick verification that predates the Musk era and has not been paid for will be “removed in a few months”, he added.

Musk’s email, sent on Wednesday, outlined that Twitter would focus on engineering, stating it was “a software and servers company”.

“Design and product management will still be very important and report to me, but those writing great code will constitute the greatest majority of our team and have the greatest sway,” it added.

Musk’s work ultimatum comes after Twitter employees were told last week to return to the office for a minimum of 40 hours a week unless they had a specific exemption.

His latest email said staffers were expected to work extremely long hours at high intensity for the social media platform to succeed in an “increasingly competitive world”.

Some staff were unsure about staying at Twitter, while others wanted to get out of a toxic environment, said one employee who recently left.

Additional reporting by Joe Miller in New York and Hannah Murphy in San Francisco