General Motors today plans to introduce a coupe version of its Cadillac ATS compact sedan, adding another crucial piece to the automaker's arsenal in an uphill battle against luxury competitors BMW, Audi and Mercedes-Benz. General Motors today plans to introduce a coupe version of its Cadillac ATS compact sedan, adding another crucial piece to the automaker's arsenal in an uphill battle against luxury competitors BMW, Audi and Mercedes-Benz.