Musk says he will be working.
When a Twitter user asked Musk, "Any big birthday plans?" on Thursday, Musk responded: "Working on Tesla global logistics."
"You need time off too, don't you?" replied the same Twitter user.
The tech billionaire responded with a frowning face.
He said he would accept a party on Twitter from his followers, however.
The working birthday may be due to Tesla's second quarter goals. On Tuesday, Musk sent an email to his entire staff there asking them to work hard to hit those vehicle production and delivery numbers. At the end of the first quarter of 2019, Tesla said it expected to deliver between 90,000 and 100,000 vehicles in the second quarter.
"As you may have noticed, there is a lot of speculation regarding the vehicle deliveries this quarter. The reality is that we are on track to set an all-time record, but it will be very close. However, if we go all out, we can definitely do it!" Musk wrote in the email, obtained by CNBC.
The effort remaining is primarily logistics, Musk said in his all-staff email.
"We already have enough vehicle orders to set a record, but the right cars are not yet all in the right locations. Logistics and final delivery are extremely important, as well as finding demand for vehicle variants that are available locally, but can't reach people who ordered that variant before end of quarter," Musk said.
The second quarter goes through the end of June.
Musk has previously positioned himself as the leader who struggles on the front line with his employees.
In the summer of 2018, when Tesla was ramping up production of its Model 3, Musk stayed on location to diagnose and fix problems in the factory production line. He called the time "painful" in conversation with "CBS This Morning" host Gayle King.
"Absolutely, of course. Yeah, I'm sleeping on the factory floor, not because I think that's a fun place to sleep. You know. Terrible," he said. "I don't believe like people should be experiencing hardship while the CEO is, like, off on vacation," Musk told King.
In November 2017, Must hosted the Tesla conference call from the Gigafactory, Tesla's battery production facility in Nevada, where he had been working on location to correct production delays.
"I always move my desk to wherever — well, I don't really have a desk, actually. I move myself to wherever the biggest problem is in Tesla," said Musk in November. "I really believe that one should lead from the front lines and that's why I'm here."
His long hours don't escape criticism, though.
Thrive Global founder and author Arianna Huffington wrote Musk an open letter pleading him to get more sleep after he admitted to working as much as 120 hours in a week.
"Working 120-hour weeks doesn't leverage your unique qualities, it wastes them. You can't simply power through — that's just not how our bodies and our brains work," Huffington wrote. "Nobody knows better than you that we can't get to Mars by ignoring the laws of physics. Nor can we get where we want to go by ignoring scientific laws in our daily lives."
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