Rethinking Market Concentration in a New Era of Scale

Author: Drew O’Connor CFA®, CFP®, CIPM®, Director of Research

In 2014, Apple’s market capitalization hovered around $600 billion, and much of the financial press debated whether any company would ever reach $1 trillion. At the time, that milestone felt distant, if not unlikely.

Today, the outlook is very different.

There are now eleven companies with market capitalizations above $1 trillion, led by Nvidia at approximately $4.6 trillion (April 2026). What was once considered an upper limit has become a more common feature of modern markets, driven by a combination of structural shifts that have reshaped how value is created and concentrated.

A Shift in How Companies Scale 

Apple’s crossing of the $1 trillion threshold in 2018 marked a turning point. It did not just represent a milestone for a single company, but reset expectations for what scale could look like in public markets. Once that ceiling was broken, it became easier for investors to envision similar outcomes for other companies with strong growth trajectories and scalable business models.

At the same time, the market moved away from traditional industrial and energy-driven frameworks toward platform-based models. Companies built on software, data, and network effects operate with fundamentally different economics. They can scale more efficiently with higher margins, extending their reach globally with relatively low incremental cost. This has allowed leading firms to grow larger and remain dominant for longer than in prior market cycles.

More recently, the buildout around artificial intelligence has accelerated this trend. Significant capital expenditures, particularly in semiconductors and infrastructure, have concentrated investment into a relatively small group of companies positioned to benefit most from AI-driven demand.

The Role of Market Structure  

Another important dynamic has been the sustained growth of passive investing. Index-based strategies allocate capital based on market capitalization, meaning that as the largest companies grow, they receive a greater share of inflows. Over time, this creates a feedback loop where size itself becomes a driver of additional demand, reinforcing concentration within major indices.

As a result, the S&P 500 is now more top-heavy than at any point in modern history. A relatively small number of companies account for a significant share of index performance, with meaningful implications for how investors think about diversification.

Rethinking Diversification

Allocations that appear diversified on the surface, particularly those tied to market-cap-weighted indices, may be more concentrated than expected. Portfolio outcomes can become increasingly dependent on the performance of a narrow group of companies.

None of this suggests that large-cap companies should be avoided. Many are high-quality businesses with strong fundamentals and durable competitive advantages. However, it does emphasize the importance of understanding how exposure is constructed and whether a portfolio’s underlying structure aligns with long-term objectives.

In an environment where market leadership is increasingly concentrated, a more intentional approach to diversification, across sectors, styles, and strategies, can help create a more balanced and resilient portfolio.