This is an area that is fraught with challenges. Serving a truly global audience means standards are difficult to measure as to what is "adult content" - it varies widely (Wikipedia in some areas is "adult content", as an example.)

In the near term, there is no filter set that we offer that mimics that functionality.

However, we recognize some variation of "best effort" adult content segmentation is a useful filter to have. We're considering it in the near term, as we have some specific educational institutional pressure to try to meet as well, since students are often easy targets for phishing, classroom computers are rife with malware, and there is also the problem of inappropriate DNS-based profiling of students and schools - problems that Quad9 can help solve.