An ABC Studios rep confirmed the move, stating that Chyler Leigh is signed for at least 13 episodes at the present time.
The news confirms our story from last week about Leigh possibly joining the cast.
It also comes in spite of a report that Grey's test audiences chewed up and spit out the Lexie character during a recent focus group.
Her flirtation with Derek Shepherd - one of only two scenes featuring Lexie Grey thus far - didn't help.
In any case, Chyler Leigh appears to be here to stay.
In related news, the spin-off, Private Practice, also added a new star in KaDee Strickland (The Wedding Bells) to play the administrator of Oceanside Wellness Center. She too will be a series regular.