Non-paywalled source [0] confirming this:

"NBIM plans to increase its holdings of nongovernment U.S. fixed income, such as corporate bonds, to 27.6% from 16.2%.

CEO Nicolai Tangen and Norway’s central bank chief, Ida Wolden Bache, said the fund could earn higher premiums by diversifying into riskier assets, such as mortgage-backed securities, which they judge as well positioned to weather as a long-term investor."

[0] https://www.cnbc.com/2026/09/04/worlds-biggest-sovereign-wea...

Indeed, but as US treasuries yield go, so do mortgage rates. Do mortgage backed securities carry more risk than US treasuries? Maybe not. Those with mortgages are highly incentivized to continue to pay their mortgages every month, while the US government doesn't appear willing to stop growing the debt. The quote in JumpCrisscross' comment explains this:

> These MBS are largely backed by government agencies, meaning Norway’s exposure to the risk of a US government default is only being reduced modestly. They do, however, offer slightly higher yields than Treasuries because of the risk that mortgages are repaid early."

TLDR More yield for similar risk profile while pushing up mortgage rates over time (all US consumer debt is priced off of US treasury yields; less demand for treasuries will push up their yields). Watch the 10Y and 30Y curves for where the market thinks rates are going.

(think in systems)