Noam Shazeer, Google's Gemini co-lead and a founding architect of modern AI, is leaving to join OpenAI just before the company's planned IPO, marking a high-profile departure less than two years after Google paid $2.7 billion（約4300億円） to bring him back.

What happened: Noam Shazeer, Google's vice president of engineering and co-lead of Gemini, announced on June 18 that he is joining OpenAI. Shazeer co-authored the 2017 paper "Attention Is All You Need," which introduced the Transformer architecture underlying virtually every major language model today. He first joined Google in 2000, left to co-found Character.AI in 2021, and Google brought him back with a reported $2.7 billion（約4300億円） acquisition of that startup.

Why it matters: The departure arrives as OpenAI confidentially filed an S-1 with the SEC and prepares for a public offering that could exceed $1 trillion（約160兆円）, with Goldman Sachs and Morgan Stanley advising. Shazeer's addition strengthens OpenAI's technical credibility at a moment when the company faces pressure from rivals including Anthropic, which is gaining ground in enterprise markets. The move signals a shift in personnel at a sensitive moment for the IPO push.

What to watch: Investors will likely closely monitor whether Shazeer's arrival shifts product momentum ahead of OpenAI's public listing. The company is competing in a crowded 2026 IPO wave that includes SpaceX.