The Defense Department said Friday the company will convert the flat-bottom vehicles to the Double V-Hull Engineering Change Proposal 1 configuration.
Work is scheduled to run through April 30, 2021.
GDLS secured a potential $508.7M contract in October 2016 to modernize 215 Stryker vehicles through April 2019.
The Army obligated the full amount of the modification award from its fiscal 2018 and 2019 weapons and tracked vehicle procurement funds at the time of award.
Stryker is designed to operate in rough terrains and travel at a speed of up to 60 miles per hour.