Could Boston, Chicago, and New York Become 2-Day Marathons?

July 2, 2026

We’re well into a global running boom, and seemingly nothing is booming more than the World Marathon Majors.

In the past two years, the London Marathon became the largest marathon ever, the World Marathon Majors added two new races—Sydney and Cape Town—to the circuit, and the U.S. majors have increased their field sizes.

The growth reached a new milestone on June 19 when the London Marathon announced it would be expanding to a two-day event in 2027, targeting a field size of 100,000 participants. The elite men and women will race on different days, but specific details on the format have not yet been announced. The race emphasized that the format is a one-time change for 2027 only.

“The 2027 TCS London Marathon Double is our most ambitious evolution to date—a once-in-a-generation one-time-only reimagining of what a marathon and city-wide celebration of activity can be,” Hugh Brasher, the CEO of London Marathon Events, said in a statement. RUNNER’S WORLD