Agent Erik Burkhardt told ESPN's Adam Schefter that Hyder's deal is for three years and $16.5 million with upside to $17.5 million with incentives.
Mayowa, who played for Seattle last season, is returning to the Seahawks on a two-year deal that will likely include at least one additional voiding year for salary-cap purposes, a source told ESPN's Brady Henderson.
Both Hyder and Mayowa will turn 30 before the start of this coming season.
Hyder set a career high with 8.5 sacks in 16 games with the San Francisco 49ers last season while playing under coordinator Robert Saleh, a Pete Carroll disciple who runs a defense similar to Seattle's. The 49ers signed the 6-2, 270-pound Hyder in free agency last offseason to be a rotational player who lined up as a tackle and end, but he became a starter because of injuries to Nick Bosa and Dee Ford and was the 49ers' most productive defensive lineman while mostly playing on the edge.
Hyder hade 8.0 sacks in 2016 with the Detroit Lions and has 18.5 since entering the league as an undrafted free agent out of Texas Tech in 2014. He has also played for the New York Jets and Dallas Cowboys.
Mayowa had six sacks, seven tackles for loss, two forced fumbles and nine quarterback hits in 13 games with the Seahawks last season, missing three games with an ankle injury. He made nine starts but saw a slight dip in playing time when the Seahawks traded for defensive end Carlos Dunlap, who became their starter.
Mayowa's Pass Rush Win Rate as an edge defender of 16.2% was 24th among qualifying players leaguewide and tops among Seahawks players. Hyder was 39th at 11.3%.
Mayowa had a career-best seven sacks with the Raiders in 2019 before he reunited with the Seahawks last March on a one-year deal worth $3.05 million. After a slow start for their pass rush in 2020, the Seahawks recorded a league-high 37 sacks over the final 10 weeks -- with Mayowa getting four during that span.
He began his career as an undrafted free agent out of Idaho in 2013, spending his rookie season in Seattle. He has 26 sacks in 100 career games over eight NFL seasons and has also played for the Cowboys and Arizona Cardinals.
Dunlap remains unsigned after his release from the Seahawks earlier this month, which saved the team $14.1 million in cap space.
Pass-rushers were the Seahawks' biggest remaining need entering the second week of free agency. Hyder and Mayowa join a group that has L.J. Collier, Rasheem Green, Alton Robinson and Darrell Taylor at end with Jarran Reed and Poona Ford at tackle. Taylor, a second-round pick last year, began practicing late in the season but didn't play as a rookie because of a leg injury from college.
The Seahawks added a voiding year into the contracts they gave running back Chris Carson and center Ethan Pocic last week, something the team has not previously done under general manager John Schneider and VP of player administration Matt Thomas. That mechanism reduces a player's immediate salary-cap charge by spreading out signing-bonus proration but creates dead money down the road, so it amounts to borrowing cap room from future years.
Information from ESPN's Nick Wagoner was used in this report.