Shein‘s quiet rise has reached a crescendo as the fast fashion e-commerce app takes the crown from Amazon as the most downloaded shopping app on iOS and Android in the United States, according to data from app tracking firm App Annie.

Its ascent is quiet because the startup, despite reportedly exceeding a $15 billion valuation, maintains an unusually low profile and doesn’t try to make itself known to the media. The app, dubbed the “TikTok for e-commerce” by China-focused internet analyst Matthew Brennan in this thorough piece on the startup, manufactures in China as many apparel retailers do.

The difference is Shein controls its own production chain, from design and prototype to procurement to manufacturing. Each step is highly digitized and integrated with another, which allows the company to churn out hundreds of new products tailored to different regions and user tastes at a daily rate. The strategy is not unlike TikTok matching content creators with users by using algorithms to understand their habits in real-time.

On May 11, Shein became the most installed shopping app on Android in the U.S., and six days later took the top spot on iOS as well. It briefly topped the Android chart in late April, read more here.