Warren Buffett’s Favorite Moat Faces Costco Loss, GBT Bet Could Rewire Growth

For a value investor, few endorsements carry more weight than Warren Buffett's. His long-standing, unwavering commitment to American Express is a powerful testament to the company's enduring economic moat. Berkshire Hathaway's initial purchase in 1991 turned into 100-bagger, a rare feat that has cemented the stock as the conglomerate's second-largest position today. Even as Buffett raised over $100 billion in cash from recent stock sales, not a single share of American Express was sold. This discipline speaks volumes about the quality of the business.

The moat itself is classic Buffett: wide and reinforcing. It is built on three pillars. First, a strong brand identity and prestige that transcends mere payment processing. Second, high switching costs embedded in its rewards and loyalty programs, which lock in customers. Third, powerful network effects-the more merchants accept AmEx, the more valuable the card becomes for users, and vice versa. This creates a self-reinforcing cycle that is exceptionally difficult for new entrants to disrupt.

The company's recent strategic shift underscores a disciplined effort to leverage this moat. Facing challenges in its core charge card business, AmEx has made a significant diversification play by integrating American Express Global Business Travel (GBT). This isn't a desperate pivot but a calculated expansion into a related, high-margin service where its brand and customer relationships can be applied. The early results show promise, with GBT reporting strong growth and reaffirming ambitious guidance for 2026. This move, viewed through the lens of a value investor, is about extending the durable competitive advantage into new revenue streams, thereby enhancing the long-term compounding potential of the business.

Assessing the Moat's Width and Current Challenges

The competitive moat of American Express is being tested on two fronts: a significant loss of a key merchant partner and a strategic push into new, adjacent businesses. The company's long-standing identity as a status symbol for the affluent is being challenged, even as it actively courts a younger demographic to replenish its customer base.

The most concrete challenge is the end of the Costco relationship. This was more than a simple merchant agreement; it was a cornerstone of AmEx's appeal to a specific, high-spending segment. Losing that partnership represents a tangible erosion of its traditional affluent customer base and a direct hit to the network effect that once made its cards so valuable. The company is responding with a multi-pronged strategy, including pitching prepaid cards to lower-end consumers-a move that could take years to bear fruit-and trying to get more small businesses to accept its cards. This shift signals a need to diversify its merchant footprint and customer appeal, a necessary but potentially dilutive effort for a brand built on prestige.

On the growth side, the acquisition of Global Business Travel (GBT) is the company's most significant strategic catalyst. GBT is no longer a minor player; it now represents a major portion of revenue and earnings. The unit's recent performance is strong, with revenue growing 34% year-over-year in the fourth quarter and management reaffirming ambitious 2026 guidance. This acquisition is a classic moat-extension play, applying AmEx's brand and customer relationships to a high-margin service business. If successful, it could offset some of the pressure from the core charge card business and provide a new, stable earnings stream.

The company's ability to navigate this transition hinges on its customer base. Here, there is a powerful tailwind. American Express is successfully attracting younger generations. As of the fourth quarter, 65% of new cards came from the Millennial and Gen Z demographic, and these cohorts now make up the largest share of U.S. consumer spending. This is a critical long-term advantage. While they may start with lower spending, they are the fastest-growing cohorts, and their lifetime value is expected to rise with their incomes. This demographic shift is not a speculative bet but a current reality that is already driving new card issuance.

The bottom line is that the moat is under pressure from one side and being actively reinforced from another. The loss of Costco is a setback that requires a strategic response, but the company is not standing still. Its focus on GBT and its success in capturing younger spenders suggest a business that is adapting its durable advantages to a changing landscape. For a value investor, the key question is whether these new initiatives can compound at a rate that justifies the current premium valuation, or if the costs of this transition will pressure margins in the near term.

Financial Performance and Valuation: The Margin of Safety

The numbers tell a story of resilience, but also of a premium price for that durability. American Express's trailing price-to-earnings ratio stands at 21.93, a multiple that reflects the market's high regard for its brand and network. Yet this figure sits well above the company's own historical average and commands a clear premium over many of its peers. For a value investor, this is the central question: does the current price offer a sufficient margin of safety given the business's challenges and growth trajectory?

Recent quarterly results introduce a note of caution. In the fourth quarter of 2025, the company reported earnings of $3.53 per share, a slight miss against the consensus estimate of $3.57. While the gap was narrow, it is a reminder that even a high-quality business can face execution headwinds. The broader financial picture, however, remains robust. The company continues to generate substantial cash flow, which supports its commitment to shareholders. The dividend is a key part of that commitment, with an annualized forward dividend yield of 1.24% backed by a quarterly payment of $0.95 per share. This yield, while modest, is supported by a forward payout ratio of 18.88%, indicating the dividend is comfortably covered by earnings.

The valuation premium must be weighed against the company's strategic investments and the pressure on its core moat. The integration of Global Business Travel and the effort to attract younger demographics are capital-intensive plays that may weigh on near-term earnings growth. At the same time, the loss of the Costco relationship represents a tangible erosion of its traditional affluent customer base. The market is pricing in the expectation that these new initiatives will successfully compound and offset these pressures. If they do, the current P/E may be justified. If they falter, the margin of safety could quickly vanish.

From a value perspective, the setup is one of high quality priced for perfection. The business model is durable, and the long-term compounding potential is clear. Yet the current price of roughly $305 per share leaves little room for error. For a disciplined investor, this is not a call to buy, but a call to watch. The margin of safety would improve only if the stock price were to retreat toward its historical average P/E, or if the company's earnings growth accelerated to materially exceed the market's current optimistic assumptions. Until then, the premium is a bet on flawless execution of a complex transition.

Catalysts, Risks, and the Long-Term Compounding Horizon

The investment case for American Express over the next decade hinges on two key questions: can management deploy capital with the same discipline that has built its legacy, and can the growth engine sustain itself as the competitive landscape shifts?

The most immediate catalyst is management's renewed commitment to returning capital to shareholders. The company has doubled its share repurchase authorization to $600 million. This move is a powerful signal. It demonstrates confidence that the stock is undervalued relative to its intrinsic worth and that the company's own cash flows can be deployed more effectively than any external investment. For a value investor, this is a hallmark of disciplined capital allocation-a practice that has consistently compounded Berkshire Hathaway's wealth.

The growth engine's sustainability, however, is the longer-term test. The company's guidance for 2026 sets a clear benchmark: revenue growth of 19% to 21%. This target, largely driven by the Global Business Travel unit, will be a key validation of its moat-extension strategy. Success here would prove that AmEx can leverage its brand and customer relationships to build a new, high-margin earnings stream. Failure would undermine the premium valuation and raise questions about the company's ability to innovate beyond its core charge card business.

The primary risk to the long-term thesis is the erosion of the premium brand moat. As noted, the end of the Costco relationship was a setback, and the company now faces competitors like J.P. Morgan that are actively targeting wealthy Americans. This is a classic threat to a status-driven business. The risk is not just about losing affluent customers, but about the brand's perceived exclusivity weakening over time. Sustained innovation in rewards, services, and digital experiences will be required to defend this advantage. The company's push into AI for customer experience and cost savings is a direct response to this pressure.

Viewed through a value lens, the setup is one of a durable business navigating a complex transition. The doubled buyback is a vote of confidence in the company's ability to generate cash and find value. The 2026 growth guidance is the first major test of its new growth model. The risk of moat erosion is real, but the company's strategic moves-diversifying into GBT, attracting younger demographics, and investing in technology-are attempts to widen the moat in new directions. The margin of safety for a 10-year investor depends on whether these initiatives compound at a rate that justifies the current premium, or if the costs of defending the legacy brand and funding growth will pressure returns.