The Seahawks were planning to cut Amadi as part of their first wave of roster reductions, according to a source, but instead found a trade partner and a reinforcement at a position that's been thinned by injuries.
Whiteside, a second-round pick out of Stanford in 2019, has a combined 16 catches for 290 yards and a touchdown in 40 games over three seasons. The Eagles moved the 6-foot-2, 237-pound Arcega-Whiteside to tight end earlier this offseason. The Seahawks plan to use him as a hybrid receiver/tight end, according to a source.
Arcega-Whiteside was viewed as a long shot to make the Eagles' final roster.
Amadi, a fourth-round pick out of Oregon in 2019, has been a rotational player at nickel and was competing with Marquise Blair and Justin Coleman for that job. The Seahawks have also looked at rookie Coby Bryant as a nickel option.
Amadi is set to make a non-guaranteed $2.54 million base salary this season after receiving a proven performance escalator raise. Seattle will take on Arcega-Whiteside's $1.2 million salary.
The Eagles see Amadi as a versatile player who can add competition to the secondary. Safety is arguably the biggest positional question mark heading into the 2022 season for the Eagles, who could use some more depth behind projected starters Anthony Harris and Marcus Epps.
The Seahawks' receiver corps has taken a hit of late with injuries to veteran Marquise Goodwin (hamstring), Freddie Swain (back) and Cody Thompson (shoulder). They've been without last year's second-round pick Dee Eskridge (hamstring) since the first practice of training camp. The Seahawks put Thompson on injured reserve Monday and waived another receiver, Deontez Alexander, as part of their roster reductions.
The Eagles selected Arcega-Whiteside 57th overall in the 2019 draft, seven spots ahead of Seahawks star receiver DK Metcalf.
NFL teams need to trim their rosters to 85 by Tuesday.
ESPN's Tim McManus contributed to this report.