So the Fed will fully resume Treasury purchasing, as a part of their balance sheet expansion starting December 1st 2025

Not only all maturing Treasuries will be rolled over at auctions, but also all Mortgage Backed Securities (MBS) principal will be reinvested into Treasury bills (<1 year duration)

This will lower the duration of the assets on the Fed's balance sheet and contribute to debt monetization

But that's not a surprise. 3 months ago I explained why interest rate cuts and the end of QT/start of QE is imminent