Short answer — it depends how you measure “growing.” By absolute net new restaurants in calendar-year 2024, the biggest chains adding the most units were Starbucks, Chipotle, Taco Bell, Chick‑fil‑A and McDonald’s. By percentage (fastest percent growth), small/emerging concepts led the list — for example drive‑thru coffee brand 7 Brew and a few seasonal/novel concepts posted the largest percent increases. (qsrmagazine.com, Datassential.com)

Details (recent, reported growth):

• Fastest by absolute unit growth (net new U.S. units, 2024): Starbucks (+589 net stores), Chipotle (+273), Taco Bell (+199), Chick‑fil‑A (+145) and McDonald’s (+102) were among the largest net openers in the QSR 50 / industry rankings for 2024. These figures come from QSR Magazine’s 2025 QSR 50 summary of 2024 performance. (qsrmagazine.com)

• Fastest by percentage unit growth (smaller/emerging chains): Datassential’s Top 500 previews show the largest percentage increases were posted by emerging concepts — e.g., 7 Brew (drive‑thru coffee) grew ~373.7% year‑over‑year (2023 vs 2022) and other small brands (Peach Cobbler Factory, Hangry Joe’s Hot Chicken, etc.) also posted very large percent gains. These high percentages reflect very small base sizes turning into many net new units. (Datassential.com, restaurantdive.com)

• Category & other notable movers: chicken and coffee concepts have been especially active — chains such as Dutch Bros (rapid openings and an aggressive growth target), Raising Cane’s, Wingstop and several regional chicken chains showed strong expansion or sales growth in recent reports. Industry roundups (QSR, Restaurant Business/Restaurant Dive) highlight these category trends. (qsrmagazine.com, RestaurantBusinessOnline.com)

Quick context and caveat:

• “Fastest‑growing” can mean net new units (absolute), percent unit growth, same‑store sales growth, or systemwide sales growth — different metrics will produce different “winners.” The numbers above use published industry reports covering 2023–2024 performance and 2024 unit changes. (qsrmagazine.com, Datassential.com)

If you want, I can:

• give a ranked list for a specific metric (units vs. percent vs. sales) and time frame (e.g., calendar‑year 2024 or year‑to‑date 2025), or
• pull the latest 2025 year‑to‑date openings for a particular region or chain.