The option was included in the three-year, $27 million extension Britt signed last summer. Declining it would have voided the final year of the deal, per Henderson, making Britt a free agent after 2019.
It also would have increased his 2018 base salary from $2.75 million to $7.75 million. Instead, Britt receives a $5 million bonus, though his 2018 cap number remains $6.17 million.
The Seahawks made Britt a second-round pick in 2014, and he has started 63 of a possible 64 games.