Just six months after leaving a high-profile job at Apple, Tesla's Autopilot software chief Chris Lattner is looking for a new job.

"Turns out that Tesla isn't a good fit for me after all," Lattner tweeted late Tuesday.

In January, Tesla picked Lattner to work on its self-driving car program, praising his reputation for "engineering excellence" in a blog post. Lattner spent 11 years at Apple, most recently creating Swift, Apple's new app programming language.

Tesla (TSLA) confirmed Lattner's departure. "Chris just wasn't the right fit for Tesla, and we've decided to make a change," the company said. "We wish him the best."

Tesla also announced that it had hired Andrej Karpathy, an expert in allowing computers to see and to learn, as director of Artificial Intelligence and Autopilot Vision, reporting to CEO Elon Musk. Karpathy was most recently a research scientist at OpenAI, a nonprofit AI research company that includes Musk as one of its sponsors.

It said that employee Jim Keller will now have overall responsibility for Autopilot hardware and software development, reporting to Karpathy.

Turns out that Tesla isn't a good fit for me after all. I'm interested to hear about interesting roles for a seasoned engineering leader! — Chris Lattner (@clattner_llvm) June 21, 2017

Tech companies and automakers have been fiercely competing for top technical expertise as part of their efforts to develop self-driving car technology.

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Apple (AAPL) and Tesla, whose headquarters are only 10 miles from one another, have been raiding one another's employees enough that Tesla CEO Elon Musk even had to address the issue with investors during a 2015 conference call with analysts.

"Tesla has recruited five times as many people from Apple as Apple's recruited from Tesla," he said in May of that year. "It's a fairly high number."

Musk is known as a demanding, even difficult boss. A 2015 biography of Musk included a tale of him scolding an unnamed Tesla employee for choosing to attend his child's birth over a company event. Musk denied that charge in a tweet when the book was published, but its author issued a statement standing by his reporting.