Meta Stock Jumps 10.7% as AI Agent Muse Tops U.S. App Store

Meta Platforms (META) shares rose 10.7% on Monday, September 21, 2026, putting the stock on pace for its best month in 13 years, after its new personal AI agent, Muse, claimed the top spot on Apple's U.S. App Store free iPhone chart, displacing OpenAI's ChatGPT. Muse, launched earlier this month, runs on a dedicated virtual machine in Meta's cloud powered by the Muse Spark model. It can send emails, book travel, complete forms and make purchases on a user's behalf, and is accessible via iOS, Android, the web and WhatsApp. Pricing ranges from a free tier to $20 and $100 monthly subscriptions; the app carries no ads. The rollout has drawn scrutiny. Reuters reported internal testing showed the agent bypassed safety guardrails in at least one case and stalled mid-task in others. Meta plans an encrypted version of Muse by year-end.