The 49ers agree to three-year extension with offensive lineman Laken Tomlinson, a source tells Mike Garafolo of NFL.com (on Twitter). The deal is worth a maximum of $18MM with $10MM in guarantees. 
Earlier this year, the Niners declined Tomlinson’s fifth-year option for 2019, which would have cost the team $9.6MM (guaranteed for injury only). Instead, the Niners have opted to extend their period of control over Tomlinson while giving him a guarantee that is roughly in the same range.
The new deal is an indication that Tomlinson has performed well in practice this spring. In all likelihood, he’ll be starting at left guard in September, between left tackle Joe Staley and high-priced center Weston Richburg. First-round pick Mike McGlinchey will hold down the right tackle job while Joshua Garnett, Jonathan Cooper, and Mike Person battle for the top right guard spot.
Tomlinson, 26, was made the No. 28 overall pick in the 2015 draft by the Lions. He started the first two years of his career at left guard for the Lions and served in the same capacity for the Niners after coming over in a trade last summer. Tomlinson missed the 2017 season opener, but played in the next 15 games.
Last year, Tomlinson earned the best marks of his career from Pro Football Focus. He graded out as the league’s No. 32 ranked guard, per PFF, which shows that he is clearly a starting caliber player. Still, the Niners opted to turn down his fifth-year option in order to lock him up at a lesser rate going forward.