Are hazelnuts the same as filberts? Yes. How much antioxidants do they contain? A high amount, at least relative to most other nuts (pecans and walnuts rank higher). Versus many other foods like meat and dairy, hazelnuts have an exponentially higher amount - as much as 100 to 300x more.
USDA Database for the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 - Prepared by Nutrient Data Laboratory, Beltsville Human Nutrition Research Center (BHNRC), Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA) - May 2010