Meta Platforms shares have risen 27% since the company launched its Muse personal AI agent on Sept. 8 and are now up 18% for the year, outperforming Alphabet, Amazon and Microsoft. The gains mark a sharp reversal from investor concern over Meta's heavy AI infrastructure spending, which had contributed to an approximately 18% year-to-date decline through mid-August. Earlier in September, Meta shares climbed roughly 36% through Sept. 24, 2026, their strongest monthly performance since July 2013, reaching $777.59 and valuing the company at about $1.98 trillion. Muse reached the top position on Apple's App Store, while analysts have projected that the AI agent could eventually generate up to $50 billion in annual revenue through a freemium offering and enhanced advertising. Investors are focused on earnings for evidence of Muse monetization, user retention and the return on Meta's AI investment.