Manufacturers use a concentrate, the same concentrate that is used in liquid Splenda. No filler, like in the pourable or packet RETAIL Splenda is required, therefore no extra carbs from filler.

Now OTHER carbs might be in the product (like from glycerin or maltitol, for example), though. One must read the official Ingredients List, as you would for any product.

Sucralose on the Ingredients List is the concentrate only, no filler.