Sigma is General Motors' mid-size rear-wheel drive automobile platform. The architecture debuted in 2002 with the 2003 Cadillac CTS and is adaptable for all-wheel drive and extended wheelbase versions.The long-wheelbase Cadillac STS replaced the front-wheel drive GM G platform Cadillac Seville. The CTS was a replacement for the rear-wheel drive V-body Cadillac Catera.The Sigma platform has a four-wheel independent suspension with control arms in front and multi-link in the rear.