Meta's stock surged sharply in September 2026 on the early success of its Muse personal AI agent, launched September 8, which quickly topped app store charts and demonstrated competitive capabilities against OpenAI tools. This momentum followed a major legal settlement easing regulatory overhangs and analyst upgrades highlighting AI-driven ad improvements and new enterprise features. The week of September 28 featured notable volatility, with closes fluctuating amid continued product updates at the Connect event and the debut of the Meta Enterprise Platform on the 28th itself. Traders are watching adoption metrics for Muse and any pre-earnings signals, as the rally has reset valuations while leaving room for further gains if AI monetization accelerates.