How do you search arXiv by sub-subject? How do you search arXiv by sub-subject?

For example, underneath the subject Computer Science, you have the subject 'Artificial Intelligence', and under the subject Quantitative Finance, you have the subject 'Computational Finance'.

How do I search for papers specifically within these subjects? Clicking on the subjects only brings up recent submissions, but I want all of them.
You can use the Advanced Search for this, specifically the 'All fields' option in the dropdown menu. Set that value to the abbreviation/code for the subcategory, e.g. cs.ai or q-fin.CP for your examples. These seem unique enough to not pick up many false positives, and will (unless you specify otherwise) also pick up crosslisted papers. Refine the query as desired.