Season four marked the first crossover event with fellow Syfy series Warehouse 13. Douglas Fargo (Neil Grayston) appeared in the August 3, 2010 episode of Warehouse 13, while Claudia Donovan (Allison Scagliotti) of Warehouse 13 appeared on Eureka on August 6, 2010. James Callis joined the cast as Dr. Trevor Grant, a scientist from 1947.
Season 4 was split into two parts, plus two standalone Christmas specials: the first nine episodes were shown in the summer of 2010, a Christmas episode was shown in December, and another 10 episodes began airing on July 11, 2011. A second Christmas special aired on December 6, 2011.