According to a City of Irvine document, 400 Spectrum Center tower will become the twin to the existing 200 Spectrum Center tower. The upcoming second tower is also from the Irvine Company and will stand at 20 stories tall.
From observation, it appears the 400 Spectrum Center is undergoing site prep as there is a heavy presence of construction equipment and the entire site is fenced off. Additionally, some of the parking pavement has been dug out.