I'm not a cohost, but I can point you to the booktubers who are cohosts!
The hosts of #historathon2023 on YouTube are:
Vin @revenantreads
Peg @TheHistoryShelf
John @NicholasOfAutrecourt
Mark @BookTimewithElvis
@billruttenberg
Mariana @marianamasbooks
Fred @ReadbyFred
Gareth @bookssongsandothermagic
Erica @passageoftime8561

The four quarters of Historathon 2023:
Q1: January - March: prehistory to 500 A.D.
Q2: April - June: 500 to 1500
Q3: July - September: 1500 to 1820
Q4: October - December: 1820 to present