For the first time in its 124-year history, there will not be an in-person Boston Marathon. The Boston Athletic Association, deferring to Boston Mayor Marty Walsh’s decision to cancel mass participation events, announced Thursday that the race will instead be held virtually, as part of a series of virtual events during the second week of September.

The 2020 Boston Marathon originally was scheduled for April 20 but was postponed to Sept. 14 due to the COVID-19 pandemic.

Registrants will be offered a full refund of their race entry fee and have the opportunity to participate in a virtual alternative, completing a marathon — and providing proof of timing — within a six-hour time period any time between Sept. 7–14. Athletes who complete the virtual race will receive an official Boston Marathon program, participant T-shirt, medal and runner’s bib.

“I’m disappointed that it’s canceled, but I am excited that they made the decision because the second round of training was about to start,” said Hopkinton resident Ali Balster, who was fundraising for Hopkinton Boys Youth Lacrosse.

Balster said she initially was hesitant to commit to the virtual race, saying “it’s a lot harder to run” without the excitement of the start in Hopkinton and the crowds along the route providing support, but because the BAA is not offering deferred entry into next year’s event she probably will run on her own in September. She also is registered to run the Chicago Marathon on Oct. 11 but expects that race will be canceled as well.

“I’ve already completed my fundraising,” she noted, “so if I can’t run 2021 I feel like I have to run a marathon for this.”

The BAA indicated it will offer a series of virtual events and activities throughout September’s Marathon Week, including exclusive panel discussions, champions interviews and a downloadable Boston Marathon toolkit that includes signature race elements such as a printable finish line, winner’s breaktape and more.

The BAA 5K scheduled for Sept. 12 was canceled as well.