In December 2022, CMS released CR13023, annual update for lab fees and policies for 2023. Find it here.
34 codes appear to be marked for "Gapfill" in this spreadsheet (see CR13023 p9 fwd). (For other codes, crosswalks are stated).
In the gapfill process, MACs are expected to gather information germane to pricing in the first quarter, and report to CMS in the second quarter. CMS posts these prices typically around May or June, for 60 days public comment. The public comments, if any, are relayed from CMS to the MACs which reflect final prices back to CMS in early fall. The final gapfill prices are posted by CMS, typically around October.
(Technically, there is an appeal process but it is not well-specified and involves contacting CMS and discussing the grievance with the final MAC price (which is very rarely changed).)
Generally, the MolDx program has taken the stance that if it wants information from outside the walls, it will contact you. The Novitas and FCSO MACs generally post a web portal for the structured submission of answers to questions. The NGS MAC in the past has posted a brief article about information gathering and submission.
Gapfill prices are set by the median of the MAC prices (based on a count of CLFS regions, of which there are 57 for dusty legacy reasons). MolDx MACs have the majority of regions and therefore control the final median.
FCSO, Novitas Mac Websites
The FCSO MAC has posted a website or portal through which it accepts information on gapfills. It has a deadline of February 13.
Similarly for Novitas and also by Feb 13: