Gabor Cselle, the former CEO and co-founder of Pebble, a competitor to X, has joined OpenAI to work on a mysterious project.

Cselle was hired by OpenAI in October, according to LinkedIn; however, he announced that news yesterday in a post on X. "Will share more about what I'm working on in due time," he wrote. "Learning a lot already."

Cselle is a repeat founder who sold his first company, a Y Combinator-backed mobile email startup called reMail, to Google. His second company, native advertising startup Namo Media, sold to Twitter before Elon Musk purchased the social network and rebranded it to X.

Almost a decade ago, Cselle was a group product manager at Twitter, building the home timeline, user on-boarding and logged-out experiences. He left Twitter in 2016 for Google where he is director at the tech giant's Area 120 incubator for spin-offs.

Cselle began working on Pebble, initially dubbed T2, with Discord's former head of engineering Michael Greer in 2022. It focuses on safety and moderation and so far attracted a tiny, but extremely lively community; its founders could secure angel investment from, among others, Rich Miner, Android's co-founder.

However, Pebble did not persevere on the path to growth. The company shut down last October, then reopened in November as a Mastodon instance.

This May, Cselle joined the accelerator South Park Commons, where he worked on a range of generative AI prototypes--an homage to the viral HQ Trivia, among others
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Csell's hiring comes on the same weekend that OpenAI rival Anthropic lands its own high-profile recruit: Embark founder Alex Rodrigues.

Rodrigues, who guided autonomous trucking firm Embark through a SPAC merger in 2021 (and subsequent fire sale to Applied Intuition in 2023), announced on Friday that he will be joining Anthropic as an AI safety researcher.