Culliver's contract is worth up to $32 million over four years, a source confirmed to ESPN.com's John Keim. Knighton agreed to a one-year, $4 million deal, he told ESPN's Josina Anderson on Thursday.
In his first full season as a starter, Culliver, the San Francisco 49ers' third-round pick of the 2011 draft, finished with a flourish after missing the 2013 season with a torn ACL.
Per Pro Football Focus, Culliver's plus-10.8 coverage grade over the final 13 games ranked fifth-best among cornerbacks, and his allowing one catch per 13.3 coverage snaps ranked sixth among cornerbacks with 300-plus coverage snaps. Also, he had a 50.7 percent catch rate on the season.
The 26-year-old Culliver, whose career-high four interceptions came in the 49ers' last seven games, has had off-the-field issues with the Niners, from his anti-gay statements at Super Bowl XLVII to his posting offensive terms about women on his Instagram account, to his arrest in March 2014 on hit-and-run and brass knuckles charges.
ESPN.com 49ers reporter Paul Gutierrez contributed to this report.