The fourth-generation C/K was introduced in April 1987 for the 1988 model year. Known officially by its GMT400 internal codename (GM never assigned this model line a generational moniker), these are informally known as the OBS (Old or Original Body Style). Slightly smaller in cab dimensions, the fourth-generation C/K increased interior space over its predecessor. After trailing Ford and Dodge by over a decade, GM introduced the C/K in an extended-cab configuration. For nearly five years, the fourth-generation C/K was sold alongside its R/V series predecessor, as the crew cab pickup (which served as the basis of the Suburban SUV) was not released until the 1992 model year.