While the Sig Classic pistols with milled stainless steel slides have exposed extractors, the Sig Pro pistols—all of which have milled stainless steel slides— have unexposed extractors, like the Sig Classic pistols with stamped/folded steel slides.
Here is a photo of a Sig Pro ejection port, showing the unexposed extractor, followed by a photo of a Sig P226 (with milled stainless steel slide) ejection port, showing the exposed extractor:
