Second-generation driver Chad Boat will contest a pair of races for Belardi Auto Racing.
Pirelli confirms the tire picks for each driver in Austria.
Graham Rahal finished eighth after a roller coaster day at Road America.
Ed Jones finished inside the top ten for the fifth time in 2017.
Vilander steps in at AF Corse for the Nürburgring as Bird prioritizes his Formula E commitments.
Minor tweaks to the British GP schedule confirmed.
None of the Andretti Autosport drivers finished in the top ten at Road America.