AAMI vs STT: Which Is the Better Buy in 2026?

Same yardstick, side by side (as of September 2026). Valuation lined up like this is most meaningful for two names in the same corner of the market, which these are. Figures are approximate; verify before investing.

The metrics above tell you which is the marginally better business. The bigger risk for most people is not picking the slightly worse stock, it is over-concentrating. AAMI and STT share themes, so owning both, or adding either to what you already hold, can quietly push a large share of your portfolio into one bet.

This is the part a generic comparison page cannot answer, because it depends on what you own. Connect your brokerage and Walnut shows your real, combined AAMI and STT exposure, flags overlap with your existing positions, and tells you if adding one would tip you past a concentration you are comfortable with, read-only by default, with your login staying at your broker. Walnut is not an investment adviser.

Acadian Asset Management (NYSE: AAMI) is the successor to BrightSphere Investment Group, which rebranded and changed its ticker from BSIG to AAMI in early 2025 after divesting six of its seven affiliates to concentrate on a single business: Acadian, a Boston-based systematic investment manager founded in 1980. Acadian runs quantitative strategies across global equities, fixed income, and alternatives, leaning on data science, machine learning, and factor models to exploit market inefficiencies while stripping out human bias. Its client base is overwhelmingly institutional, and roughly 90% of revenue comes from equity strategies, so its fortunes track global equity markets closely.

Full AAMI guide

State Street Corporation is a global financial services firm built on two engines. The first is investment servicing: it acts as custodian and administrator for institutional investors, holding a record roughly $54.5 trillion in assets under custody and/or administration (AUC/A) as of April 2026 and earning fees for safekeeping, fund accounting, and related back-office services. The second is State Street Global Advisors, its asset-management arm, which ran about $5.6 trillion in assets under management and is best known for the SPDR ETF lineup, including SPY, the original US-listed exchange-traded fund. The company also generates net interest income from the deposits institutional clients park with it.

Full STT guide

Both fit overlapping themes, but they are not interchangeable. The useful comparison is which set of drivers and risks you want exposure to.

• AAMI drivers: Record AUM and net flows; Operating leverage on management fees.
• STT drivers: Record custody and AUM scale; Net interest income tailwind.

A faster-growing, richer-valued name usually swings harder, so it suits a longer horizon and a higher tolerance for volatility; a steadier, more cash-generative business suits a more conservative or income-minded investor. The honest test is which set of risks you could hold through a drawdown: Acadian is concentrated: over 90% of revenue comes from equity strategies, a large share of AUM sits in a handful of top strategies, and roughly 70% of AUM is denominated in non-U.S. For STT, state Street's fee revenue is tightly linked to market values, so an equity drawdown or outflows from passive funds would pressure earnings directly.

Growth-minded investors who believe the theme has years to run tend to accept the richer multiple for more upside; value-minded investors lean toward the cheaper forward earnings and steadier profile. Pick AAMI if you believe its drivers more; STT if you believe its. Many investors hold both, but since they share themes, that is a concentrated bet, not diversification. Decide deliberately and check overlap. For the full detail, see the AAMI and STT guides.

AAMI. Q1 2026 revenue rose about 39% year over year to roughly $167 million as AUM grew about 61%, with economic net income up sharply on operating leverage. The stock climbed well over 100% in the prior year, leaving a trailing P/E near 32x against a much lower forward multiple that assumes continued fee growth. The small (~$0.40 annual) dividend means this is a growth-and-flows story, not an income name.

STT. As of April 2026 State Street traded around a high-teens price-to-earnings multiple, typical for a scale custody bank valued on stable fee income plus interest earnings rather than rapid growth. The stock reached an all-time high near $175 after Q1 results beat expectations. Its valuation tends to move with expectations for equity markets, passive flows, and interest rates.

Headline figures (approximate, July 2026): AAMI shows assets under management ~$196B, revenue (q1 2026) ~$167M, management fees (q1 2026) ~$159M, market cap ~$2.7B; STT shows revenue (ttm) ~$14B, q1 2026 revenue ~$3.8B (up ~16% YoY), q1 2026 diluted eps ~$2.49 (adjusted ~$2.84), market cap ~$50B.

AAMI and STT are related but distinct: same themes, different businesses and risks. Neither wins in the abstract; the right pick is whichever thesis you actually believe, sized so you are not over-concentrated in one theme. Walnut can show your combined AAMI and STT exposure against your real portfolio. It is not an investment adviser.