New Associate Judges (Federal Court) Regulations were registered and will published shortly in the Canada Gazette. With the renaming of Prothonotaries to Associate Judges and formalizing the role, these regulations set out the number of Associate Judges in the Federal Court and the role of supernumerary AJs.
The regulations are linked here. This will be updated once they are available from the Canada Gazette.
The regulations say that there can be up to nine Associate Judges. While there are currently nine Associate Judges, Associate Judge Milczynski elected supernumerary status in April, and it has been announced that Associate Judge Tabib will be going supernumerary later this year. Associate Judge Aalto retired earlier this year.
Update: the regulations have now been published in the Canada Gazette along with the Regulatory Impact Analysis Statement.