Philadelphia traded for Hayes' negotiating rights on June 3, surrendering a fifth-round pick to the Winnipeg Jets in the process.
The 27-year-old, 6-foot-6 center tallied a career-high 55 points in 71 games during the 2018-19 season, which he split between the Jets and New York Rangers.
Meanwhile, Flyers general manager Chuck Fletcher said on June 1 that he'd be "very aggressive" during his first offseason in the role, and he's certainly followed through.
Fletcher traded Radko Gudas for Matt Niskanen on Friday, and then landed Justin Braun from the San Jose Sharks on Tuesday in exchange for two draft picks. Fletcher has also said he's open to trading the 11th overall selection in the upcoming draft.