In the week since the United States presidential election, Elon Musk has used X, the social media platform he owns, to reiterate his support for President-elect Donald J. Trump.

Some of the platform’s users have decided that they would rather post elsewhere.

Among the largest beneficiaries of that desire is Bluesky, a rival service that has gained more than a million new users in the week since the election, a company spokeswoman, Emily Liu, said on Tuesday. The majority of the new users live in the United States, Canada and Britain, she added.

“We’re seeing increased activity levels across all different forms of engagement,” she said in an email.

Bluesky, which began in 2019 as a project by the Twitter founder Jack Dorsey, is among several challengers that have each experienced bursts of momentum since Mr. Musk’s acquisition of Twitter in 2022 and subsequent rebranding of it.

The accounts created on Bluesky this week, many of which are left-leaning, shared cat videos alongside their hopes that the platform might offer a reprieve from the misinformation and hateful speech that have swirled on X since Mr. Musk’s takeover.

New or freshly active users on the platform include celebrities (the rapper Flavor Flav, the author John Green), Democratic political figures (Representative Alexandria Ocasio-Cortez of New York, Chasten Buttigieg, husband of Pete Buttigieg, the transportation secretary) and media personalities (Mehdi Hasan, Molly Jong-Fast).

“Hello Less Hateful World,” Mark Cuban, the billionaire and Kamala Harris surrogate, posted on Tuesday.

Bluesky gained its first wave of high-profile users last spring, and switched from being invitation-only to open to the public in February. It now has 14.7 million users, the company said.

That is still far fewer than Threads, Meta’s competitor to X, which this month reported that it had reached 275 million monthly active users. (A Meta spokesperson declined to share whether than number had changed post-election.)

There has been a “feeling of momentum” on Bluesky since the election, said Shannon C. McGregor, an associate professor at the Hussman School of Journalism and Media at the University of North Carolina, Chapel Hill. Many of the people leaving X are disappointed by the outcome of the election, she said, and now associate the platform with Mr. Musk’s support of Mr. Trump.

Others are frustrated by the type of content that seems to be rising to the top of their feeds. “You were getting this awful timeline of far-right, white supremacist, conspiracy theory posts — which the great majority of people don’t want to interact with on a daily basis,” said Dr. McGregor, whose research focuses on the intersection of social media and politics.

Bluesky appears to be courting users who worry about the ramifications of Mr. Musk’s proximity to the incoming president. After The New York Times reported that Mr. Musk would spend election night with Mr. Trump, Bluesky’s account posted a message on X: “i can guarantee that no bluesky team members will be sitting with a presidential candidate tonight and giving them direct access to control what you see online.”

Bluesky users are doing their best to welcome the flurry of new arrivals. Many are posting welcome messages, introductions or “starter packs” — lists of accounts that might appeal to someone based on their locations or interests.

“I see a lot of people trying to help other people find their bearings in a new place,” said John, 45, who lives in Minnesota and runs a Bluesky account that shares scenes from “Star Trek.”

John, who declined to share his last name publicly, began posting about “Star Trek” on Twitter in 2017. But the experience worsened significantly after Mr. Musk’s takeover, he said. His posts seemed to get responses from fewer and fewer genuine “Star Trek” fans, and more bots and users who had purchased verification.

He joined Bluesky last year, and estimated that he had gained more than 2,000 followers since the election. “In the last week, it has felt more like what I used to like about Twitter,” he said.

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