How detailed are you supposed to be w.r.t. your research interests in a SoP? I'm applying to PhD programs in CS this round and was finishing up my application materials when I had a question regarding the SoP.
Many people have advised me to state why I want to pursue study at that particular institution and what I want to study. My main research interests in my own subfield tend to be rather specific (discovering latent bias variables in natural language processing tasks) but I'm also open to exploring other options as well.
I have also heard stories where a competitive applicant is not offered admission because how they explain their plans of research are &quot;too specific&quot; and there aren't any faculty members that would be willing to work on that particular aspect.
This led me to wonder how specific I should actually be writing my SoP, or if I should include something like &quot;My main interests are in X but I am also open to exploring other topics in the larger field.&quot;
Any opinions are welcome, thanks.
I do not think you can be too specific about your research interests.
You said

not offered admission because how they explain their plans of research are &quot;too specific&quot;

What has actually happened here is that the applicant has applied to the wrong university.  You should follow these steps:

Identify faculty working in your area of interest.
Contact them and ask them if they are recruiting PhD students in that area (if it is not already stated publicly).
Apply, stating in your application that you wish to work in an area (or a few areas) where you know they are recruiting.

Then your application will never be &quot;too specific&quot;.
If your research interests are not specific enough, this might imply you do not know what is involved in a PhD and you might not succeed as a PhD student.