Jeff Bezos politely congratulated Elon Musk on SpaceX's first civilian mission. The two billionaires' companies are currently locked in a bitter feud.

• SpaceX's first-ever all-civilian flight, Inspiration4, took off on Wednesday.
• Jeff Bezos tweeted his congratulations to SpaceX CEO Elon Musk, to which Musk replied: "thank you."
• Bezos and Musk have a history of rivalry, and their companies are embroiled in a bitter feud.

Amazon founder Jeff Bezos tweeted his congratulations to Elon Musk on Thursday for SpaceX's first-ever civilian mission, Inspiration4.

The Crew Dragon spaceship took off on Wednesday, carrying four civilians and no astronauts into orbit.

"Congratulations to @ElonMusk and the @SpaceX team on their successful Inspiration4 launch last night. Another step towards a future where space is accessible to all of us," Bezos said.

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Musk replied: "thank you."

-Jeff Bezos (@JeffBezos) September 16, 2021

Musk and Bezos have a long history of rivalry, and this polite exchange came after Musk took multiple jabs at Bezos in recent weeks.

Musk tweeted on September 1 that Bezos' "full-time job" was suing SpaceX, echoing an earlier tweet from August in which he said Bezos stepped down as CEO of Amazon to "pursue a full-time job filing lawsuits against SpaceX."

Bezos has not sued SpaceX. He is executive chairman of Amazon, which has filed a protest letter to the Federal Communications Commission (FCC) trying to stop SpaceX's internet satellite project, Starlink, from launching more satellites into orbit. Amazon has a rival internet satellite program called Project Kuiper.

In a letter to the FCC earlier this month, Amazon said companies led by Musk think "rules are for other people."

Bezos is also CEO of his own space exploration company, Blue Origin, which is competing with SpaceX for NASA contracts. In July, Bezos offered to cover billions in costs from his personal wealth if NASA was willing to reconsider an exclusive contract it had previously awarded to SpaceX.

Blue Origin sued NASA in August over the agency's decision to award the contract to SpaceX.

In July, Bezos boarded Blue Origin's first civilian flight. Musk mocked the launch, laughing at a meme on Twitter that made fun of the fact that Bezos' flight would only touch the edge of space.

NASA on Tuesday awarded five companies contracts to build moon landers, including SpaceX and Blue Origin. It awarded $25.6 million to Blue Origin and $9.4 million to SpaceX.