Shiraz is most commonly blended with Cabernet Sauvignon in the New World, especially in Australia. Shiraz Cabernet denotes that Shiraz forms the bulk of the blend, but Cabernet Shiraz is just as common.The winemaker must decide at which point to blend the grapes. This will either be pre-fermentation or post-fermentation; there are many different variables that will dictate this decision.
Typically Cabernet Sauvignon wines will be high in tannin, especially when the grapes have received long periods of maceration and the decision to blend with Shiraz potentially depends on many factors. These include flavour components, and possibly using Shiraz to make the wine more suitable for early drinking.