For decades, investors have relied on familiar benchmarks like the S&P 500 to gauge the health and direction of the U.S. stock market. But as the nature of the market itself evolves, with private companies playing an ever-larger role, some experts have begun to question whether these legacy indexes still offer a complete picture. On September 10, 2025, Morningstar and PitchBook took a bold step to address this gap, unveiling the Morningstar PitchBook US Modern Market 100 Index—a new hybrid barometer that tracks both public and private U.S. companies in a single, unified framework.
This move marks the first time a major benchmark has included both publicly traded giants like Microsoft, Nvidia, and Apple alongside late-stage, venture-backed powerhouses such as SpaceX, OpenAI, and Stripe. The index, which comprises 100 of the largest U.S. companies—90 public and 10 private—allocates weights based on market capitalization for public firms and on valuation for private ones. The goal? To create a more accurate reflection of the modern equity landscape, where the boundaries between public and private investment are rapidly fading.
According to Morningstar, the new index isn’t just a technical innovation—it’s a response to sweeping changes in how companies raise capital and how investors seek exposure to the economy’s biggest drivers. As Sanjay Arya, Morningstar’s head of index innovation and the chief architect of the Modern Market 100, explained to PitchBook News, “The convergence of these two worlds is no longer theoretical—it’s happening now.” Arya added, “If people want to think holistically about what the market looks like, the most influential and fastest-growing companies are in this late-stage segment.”
The numbers back up Arya’s point. Over the past 25 years, the U.S. equities market has seen a dramatic shift: Venture capital-backed startups, which once made up less than 1% of the market, now represent almost 9%, according to PitchBook data. Publicly traded companies, once the clear majority, have been outnumbered by a new generation of private-market leaders. This is partly thanks to the ability of companies like OpenAI and Stripe to raise massive sums of capital without going public, allowing them to stay private for longer and continue to innovate outside the glare—and constraints—of the public markets.
“Companies don’t feel the urge to go public because they can raise a lot of capital,” Arya told CNBC. “So, to ignore them, I think you’re missing out on some of the fastest, most dynamic companies out there.” Arya also noted that indexes are supposed to give investors an indication of where the economy is heading and what market sentiment looks like. “And you can’t do that on public markets alone if a big chunk of it is outside public markets.”
Indeed, the numbers are striking. The U.S. public stock market is currently valued at around $60 trillion, while the private equity universe is estimated at $8 trillion. That $8 trillion slice includes some of the most innovative and fastest-growing companies in the world—firms that, until now, have been largely invisible to traditional benchmarks. The Modern Market 100 seeks to remedy this by giving private companies a 10% weighting, mirroring their real-world share of the total equity market.
As global financial markets increasingly embrace blended strategies that straddle public and private investment, investors are on the hunt for research tools and data platforms that can help them navigate this new landscape. Morningstar’s new index is designed to fill that void, offering a unified framework for benchmarking performance across both asset classes. The index applies a rules-based process that includes liquidity screens, quarterly rebalances, and daily calculations, with pricing for private companies sourced from verified secondary market transactions through platforms like Caplight and Zanbato.
But this innovation doesn’t come without its challenges. Pricing private assets is notoriously tricky, given their lack of daily market quotes and the relative opacity of private valuations. Arya acknowledged that his team spent roughly four years developing a transparent, rules-based methodology for the new index. “We have this big component of innovation economy, and not being able to fully capture that, which is mostly right still in the late-stage venture space, I think it just kind of provides a fuller picture,” Arya explained. “That actually helps you understand how these contours are kind of shifting over time. I think, provides great insights for investors.”
The index’s composition leans heavily toward technology and growth companies, a reflection of the sectors that dominate both the public and private late-stage markets. The top public constituents include Microsoft, Nvidia, Apple, Amazon, and Meta Platforms, while the top private names are SpaceX, OpenAI, xAI, and Stripe. This tilt toward innovation and growth means the index carries inherent risks—especially if the tech sector faces a downturn—but it also positions the benchmark to capture outperformance if current trends continue.
And so far, the performance numbers are impressive. According to Morningstar’s white paper, the Modern Market 100 posted a five-year return of 19%, outpacing the 16% return of the Morningstar US Market Index (which tracks only public companies). Over the past year, the Modern Market 100 returned 28.2%, compared to a 20% gain for the S&P 500. Arya pointed out that the index allows investors to track opportunities that simply aren’t captured in major benchmarks. For example, OpenAI—a private company valued at a reported $500 billion—is now bigger than Exxon Mobil, Palantir, or Procter & Gamble, yet most investors have little or no exposure to it through traditional indexes.
Morningstar and PitchBook hope the Modern Market 100 will serve as the basis for new investable products and inspire a broader rethink of what it means to benchmark market performance in the 21st century. Ron Bundy, President of Morningstar Indexes, put it succinctly in a company statement: “As private investments make their way into more investor portfolios, investors need better data and relevant benchmarks to capture the modern opportunity set. Our new index empowers investors with a unified framework that reflects both public and private market leaders, so investors can evaluate public and private investments on the same level playing field.”
Joanna McGinley, Executive Vice President at PitchBook, echoed this sentiment, emphasizing the unique value of combining PitchBook’s proprietary data on venture-backed companies with the transparency of public markets. “Modern Market 100 brings together our proprietary insights into venture-backed companies with the transparency of public markets, offering investors an investable view of how today’s most important companies perform across the private-to-public lifecycle,” she said.
The debut of the Modern Market 100 comes at a pivotal moment. In August, former President Donald Trump signed an executive order paving the way for alternative assets, including private equity, to be added to 401(k) retirement plans—a move that could further accelerate demand for blended benchmarks. Since 2021, crossover investors such as sovereign wealth funds, private equity buyout firms, and hedge funds have participated in roughly 5,000 private market transactions totaling $450 billion, according to Morningstar.
As Sweden’s fintech giant Klarna prepares for its anticipated IPO at a valuation as high as $14 billion, the line between public and private markets grows ever blurrier. The Modern Market 100 aims to help investors—and the broader financial industry—keep pace with this new reality, offering a more holistic, dynamic, and accurate lens on the true shape of the U.S. equities market.
With its launch, the index could mark the beginning of a new era in market benchmarking, one that recognizes the full spectrum of innovation and value creation—whether it happens on the trading floor or behind closed doors.
