U.S. private markets have reached a record $10 trillion in assets under management, a milestone that would have seemed implausible a generation ago. According to Hamilton Lane, the figure reflects years of sustained capital inflows from institutional investors, sovereign wealth funds, and, increasingly, high-net-worth individuals drawn by the promise of outsized returns. Yet beneath the headline number lies an uncomfortable reality: over the past decade, the S&P 500 has outperformed private equity by roughly 200 basis points, returning 15.3% annually compared to 13.2% for private equity.

The gap challenges a foundational premise of the asset class. Private equity has long justified its higher fees, longer lock-up periods, and reduced liquidity by promising a return premium over public markets — the so-called illiquidity premium. If that premium has turned negative over a meaningful time horizon, the value proposition becomes harder to defend.

The illiquidity premium under pressure

For decades, the standard pitch to limited partners was straightforward: accept restricted access to your capital for seven to ten years, pay management fees of around two percent plus carried interest, and in exchange receive returns that meaningfully exceed what a passive index fund could deliver. The model worked well through much of the 2000s and early 2010s, when public markets were still recovering from the financial crisis and private equity managers could acquire companies at relatively modest valuations.

The landscape shifted as public equities entered a prolonged bull run, driven in large part by the dominance of large-capitalization technology companies. The S&P 500's performance over the last decade has been heavily influenced by a handful of firms whose growth rates and margin profiles have been difficult for private portfolios to match. The AI boom has only intensified this dynamic, channeling enormous value creation into publicly traded platforms with the scale and data infrastructure to capitalize on the technology.

Private equity's return figures also carry methodological caveats. Unlike public market returns, which are marked to market daily, private fund valuations rely on periodic appraisals that can smooth volatility and delay the recognition of losses. Some researchers have argued that adjusting for this smoothing effect would widen the performance gap further. Others contend that comparing time-weighted public returns to the internal rates of return typically reported by private funds is inherently imprecise. The debate is long-running and unresolved, but the direction of the data is difficult to dismiss.

Concentration risk in venture capital

The concentration problem extends beyond performance into deal structure itself. Recent PitchBook data indicates that excluding the five largest venture deals would reduce the first quarter's total deal value by more than 73 percent. That level of concentration means the headline figures for venture capital activity are driven by a vanishingly small number of transactions, most of them tied to artificial intelligence companies commanding extraordinary valuations.

This pattern is not entirely new — venture capital has always followed a power-law distribution, where a small fraction of investments generates the bulk of returns. But the current degree of concentration raises questions about whether the broader venture ecosystem is functioning as intended. If capital is flowing overwhelmingly to a handful of late-stage AI rounds, early-stage founders in other sectors may find fundraising increasingly difficult. The risk is a narrowing of the innovation pipeline even as aggregate capital figures suggest abundance.

For institutional allocators, the $10 trillion milestone presents a paradox. The asset class has never been larger, yet the case for allocating marginal dollars to it has arguably never been weaker on a pure performance basis. Defenders of private markets point to diversification benefits, access to companies that stay private longer, and the potential for operational value creation that public market investors cannot replicate. Critics counter that much of the recent growth in AUM reflects momentum and fee-driven incentives rather than demonstrated alpha.

The tension between scale and performance is unlikely to resolve cleanly. Private markets now represent a structural feature of institutional portfolios, embedded in pension fund mandates and endowment models that are slow to change. Whether the return gap narrows — through a correction in public equities, a rebound in private fund performance, or both — or widens further may depend on forces largely outside the industry's control: the trajectory of interest rates, the durability of the AI trade, and the willingness of limited partners to accept liquidity constraints without a compensating premium.

With reporting from Fortune.

Source · Fortune