Hello, on the converter, it says "for Sigma lenses only", but it's not the same line; the 70-200mm F2.8 APO EX DG OS dates from the Sigma era before Art/Sports/Comtemporary. Here is a compatibility list: https://www.sigma-global.com/en/support/download/tele_converter_tc_1401_tc_2001_en.pdf In that sense, I'd have doubts that the AF would work perfectly; it's already struggling in set with the 150-600 Sports in the corners to bring into focus - in the centre, it works perfectly. With a lens from the previous line, I'm afraid it would cause problems. Optically, it would probably work, but all in automatic ... ??? Otherwise, I've had good experiences with Kenko converters for this kind of case (slightly older lenses).

Hallo, In der liste der 100-400mm F5-6.3 ist compatibel mit der TC-1401 aber nur mit MF. https://www.sigma-global.com/de/lenses/cas/product/popups/tele_converter/

No. The converter is exclusively designed for Sigma telephoto lenses of the HSM series (Contemporary/Sports/Art). Even with other Sigma lenses, the converter is not supposed to work properly. With the right lens, the converter delivers excellent results.