Originally opened in 1935, the 8,500-seat stadium was expanded in 2006 to its current capacity. In addition, the stadium was renamed Alex G. Spanos Stadium after Alex Spanos, a Cal Poly alum and the owner of the San Diego Chargers, in a ceremony on November 18, 2006. The recognition and subsequent renaming was a result of a $4 million donation to renovate Mustang Stadium by Mr. Spanos. This marked the largest single donation in the school's history.
In 2013 Cal Poly replaced the south end zone stands with permanent aluminum stands. Cal Poly had rented the previous stands since the mid-1990s. As a result, building permanent stands is expected to save money over time. These stands also improved handicapped access. Additionally, Cal Poly renovated the lower portion the older east sideline stands to add handicapped seats and improve accessibility and egress. The new south stands increased capacity by 345 seats however the renovation of the east stands resulted in a no net increase or decrease in seats.
Proposals to further increase the stadium's capacity to 22,000 are still being considered as of 2013.