Assefa smashed the women's world record at the 2022 Berlin Marathon in clocking two hours, 11 minutes and 53 seconds, and returns to the capital, where she claimed her first London title last year in a women's-only world record run of 2:15.50.
Her only recent defeats have come at the hands of the women she will face again in April.
Kenya's Jepchirchir edged Assefa in sprint finishes at both the 2024 London Marathon and the 2025 World Championships in Tokyo, while Dutch runner Hassan outsprinted Assefa at the 2024 Paris Olympics.
"For the first time since Paris, all three of these extraordinary athletes will be on the same start line," said Hugh Brasher, CEO of London Marathon Events. "With the calibre of athletes coming to London, it would be no surprise if the women-only world record is broken again."
Assefa said she is eager to avenge recent losses.
"Winning last year's London Marathon was one of the proudest moments of my career," she said. "To do it again, I know I'll have to beat great champions like Peres and Sifan. We've had some great battles - I hope this year I can come out on top."
Hassan, the 2023 London champion, arrives with one of the most formidable CVs in the sport, having won in Chicago (2023) and Sydney (2025).
Jepchirchir, meanwhile, holds world titles in both the marathon and half-marathon and has previously won in Boston, New York and at the Tokyo Olympics.
The elite field will also feature Kenya's Joyciline Jepkosgei and Hellen Obiri. Jepkosgei ran the fourth-fastest women's marathon in history - 2:14:00 - to win Valencia last year, while Obiri, a two-time New York City champion, is making her London debut.
Obiri won bronze in the Paris Olympic marathon.
They join a strong domestic line-up, featuring Britain's Eilish McColgan, Jess Warner-Judd and Abbie Donnelly.
The elite men's field will be announced on Thursday.