The move comes after fellow superstar Tyler “Ninja” Blevins made waves with his own defection from Twitch to Mixer in August. Although Mixer’s estimated 30 million viewership hours logged in September still pales in comparison to Twitch’s 778 million—per StreamElements’ latest report—the move is a sign of the escalating competition between tech giants looking to own the game-streaming market.

Grzesiek, who made his name playing Counter-Strike: Global Offensive in professional competitions, announced the exclusive deal in a video posted to his Twitter on Thursday ahead of his first Mixer stream later this evening.

“Mixer provides the flexibility to center my attention around them,” Grzesiek said in a statement. “I am excited to join the Mixer community, as well as continue to build relationships with both players and fans.”

A Twitch spokesperson declined to comment but linked to a report on data showing a decline in Mixer’s viewership in September. Loaded Management, which reps both Grzesiek and Blevins, declined to reveal the terms of the deal.

“Mixer continues to grow and build upon its already stellar creator community with Shroud,” Loaded CEO and founder Brandon Freytag wrote in a statement. “Shroud is an incredibly skilled player who has dominated some of the world’s most popular games.”

With more than 7 million followers on his Twitch channel and an average viewership of around 26,000 users per stream, Grzesiek is currently the eighth-most-watched streamer on Twitch, according to analytics site TwitchMetrics. He’s inked sponsorship deals with brands like Postmates, Madrinas Coffee and OnePlus in addition to a slew of gaming companies.

“We’re excited to welcome Shroud, his community and next-level gaming skills to Mixer,” a Microsoft spokesperson said. “Mixer is a place that was formed around being positive and welcoming from day one, and we look forward to the energy Shroud and his community will bring.”

StreamElements estimated that Mixer, which currently controls about 3% of the market, saw a bump of about 3 million viewership hours in the month after signing Blevins, who averaged around 40,000 viewers per stream on Twitch at the time of his departure. But the number subsequently dipped in September to well below what it had been in the month before the Ninja deal (38 million in July compared to 30 million in September).

Twitch’s viewership hours also grew in the month after losing Ninja, from 851 million to 932 million, and the platform still dominates the space with a market share of 76%.

Blevins’ wife, Jessica Blevins, told Business Insider earlier this month that Blevins had chosen to leave in part because the contract that Twitch had proposed would have limited his licensing deals.

“With the wording of how that contract was going, he wouldn’t have been able to grow his brand much outside of gaming,” she told the outlet.

Tyler Blevins also tweeted in response to Grzesiek’s defection, calling it “a massive move for the platform and the streaming industry.”