Meta shares fall 4.2% as OpenAI's 'o' agent looms over Muse-driven rally

Investing.com·28 Sep 2026·

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Summary · why it matters

Meta Platforms shares fell 4.2% to $720.36 on Monday as OpenAI's anticipated reveal of a competing always-on AI assistant added fresh competitive pressure to a stock that had surged roughly 30% in September alone. The catalyst was a September 27 report from BleepingComputer describing OpenAI's rumored "o" assistant as a cloud-based agent capable of executing long-horizon tasks, including handling email, even after a user closes the ChatGPT app, with OpenAI expected to formally unveil the product at its DevDay 2026 keynote on Tuesday, September 29. Meta's September rally was built almost entirely on the breakout success of Muse, its own personal AI agent, which since its September 8 launch has accumulated over 3.4 million downloads and taken the number-one spot in the U.S. App Store, surpassing ChatGPT, pushing META to an intraday high near its 52-week peak of $779.82 and prompting Wells Fargo to lift its price target from $640 to $796. Meta also announced the launch of its Meta Enterprise Platform on Monday, bringing its AI models and agents, including Muse and Meta Business Agent, to enterprise customers, and appointed Chirantan "CJ" Desai as Chief Enterprise Platform Officer reporting directly to Mark Zuckerberg; Desai's sudden departure as CEO of MongoDB sent MongoDB shares tumbling 18% to $336.79 intraday, and MongoDB has re-appointed founder Dev Ittycheria as interim CEO. Goldman Sachs raised questions last week about the return on Meta's massive AI investments, expected to reach $130 billion to $145 billion in capital expenditures for the full year, contributing to an early reversal of the September rally even before the OpenAI news broke.

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