Beyond Sovereigns—Norway’s Oil Fund Makes Our MBS Case

Last month, Norges Bank Investment Management (NBIM), manager of Norway’s Government Pension Fund Global, recommended a notable asset allocation shift. In a letter to the country’s finance ministry, NBIM proposed cutting the government bond weighting in its benchmark bond index from 70% to 50%, redeploying roughly $80 billion away from US Treasuries (USTs) and into other developed market fixed-income, chiefly agency mortgage-backed securities (MBS), in an effort to boost returns. For reserve managers evaluating their own fixed-income frameworks, we believe this news bears close watching.

NBIM was explicit that the proposal is not a reduction in US exposure. Dollar exposure would fall by only half a percentage point, and Norway’s finance minister has separately reaffirmed no intention to reduce US allocations. What would change is the composition of high-quality fixed-income used to meet liquidity and capital-preservation objectives. NBIM notes that agency MBS carry credit quality “close to that of US government bonds,” reflecting the guarantee structure behind Fannie Mae, Freddie Mac and Ginnie Mae issuance, while offering a yield advantage tied to prepayment risk rather than credit risk. That distinction is central to the case for agency MBS as a reserve asset: It is a source of incremental income that does not introduce credit-cycle exposure, a case we also made in a blog recently: Agency MBS—Expanding the Reserve Management Toolkit.

The framing NBIM used for its 50/50 split is important. The letter states that a 50% government bond allocation is sufficient to meet liquidity needs, including during periods of market turbulence, with the remaining portion of the portfolio structured to capture a broader set of risk premia. NBIM defined a liquidity buffer, bounded requirement and the remainder of the portfolio as return-seeking by design, a framework increasingly visible across sovereign and official institutions as they contend with higher structural rates and the need for incremental income.

The proposal also lands at a relevant point in the cycle. Following the Federal Reserve’s run-off of MBS holdings, we believe yields across agency MBS remain attractive. Current refinancing activity is structurally low, with most outstanding mortgages locked in well below prevailing mortgage rates—a dynamic that constrains prepayment risk and supports more predictable income generation.

Exhibit 1: Mortgage Refinancing Risk Remains Contained

Source: Bureau of Economic Analysis, Freddie Mac and Mortgage Bankers Association. As of 31 Aug 26. 

For reserve managers, the practical takeaways from NBIM’s letter are fourfold. (1) Diversification benefits are real: Agency MBS returns have historically shown high correlation to USTs but low correlation to equities and gold, offering a genuine complement rather than a substitute. (2) Market depth is not a constraint: Agency MBS represent the second -largest and most actively traded segment of the US fixed-income market. (3) Benchmark construction matters: NBIM’s proposal to weigh government bonds by market value of outstanding debt, rather than by GDP, echoes a broader shift already underway among large official institutions reassessing legacy frameworks. Finally, (4) the current yield and income potential of agency MBS look appealing, offering similar or higher yields compared to corporate bonds of the same credit quality.

Exhibit 2: Agency MBS Offer Compelling Risk-Adjusted Yields Relative to Corporate and US Treasuries

Source: Bloomberg indices. As of 31 Aug 26. Yield represents yield-to-worst (YTW) and duration represents modified adjusted duration. Index $price is rounded up. YTW is the lowest potential yield that can be received on a bond without the issuer actually defaulting. 

NBIM’s letter remains a proposal, subject to review by Norway’s Expert Council. A final parliamentary decision is expected in 2027. But when a $2.3 trillion fund with one of the most scrutinized mandates globally puts forward this argument, we think it reinforces the momentum for broadening the reserve managers’ toolkit beyond sovereign bonds.