In the US, a duty of disclosure to submit information material to patentability extends until the patent is granted. This means that the duty still applies after notice of allowance (NoA) and after issue fee payment, but before issue (usually 6 weeks after issue fee payment). See here.
Therefore, what if the applicant discovers new prior art either after NoA or after issue fee payment, but before issue? Is the applicant required to submit an IDS disclosing this information? What if the new prior art is discovered 1 day before the scheduled issue date?
In general, the applicant must submit known material prior art in order to avoid risk of inequitable conduct (IC) charges. However, when the prior art is discovered close to issue, it appears there may be a "fuzzy" requirement, as it is likely impractical to submit prior art discovered 1 day before issue. Further, third parties may exploit the duty of disclosure by waiting until the end of prosecution, then serving the applicant with material art, which will require additional prosecution fees (e.g. RCE) and time, or else the applicant will be vulnerable to IC charges at a later date.
Note that the USPTO currently offers a "QPIDS" program for IDSes submitted after issue fee payment. However, I have not seen anywhere that the QPIDS route is a "requirement", only an option that "may" be utilized.