SoftBank Group on Monday became Japan's most valuable public company, overtaking Toyota Motor by market capitalization after Chief Executive Masayoshi Son stood beside French President Emmanuel Macron in Paris and committed 75 billion euros, or about $87 billion, to build out 5 gigawatts of artificial-intelligence data center capacity in France. The Tokyo-listed shares closed 14 percent higher, capping a year in which the stock has risen more than 70 percent and a two-month stretch in which the Nasdaq Composite jumped 25 percent, its best April-May run in more than two decades.

The announcement, and the rally that absorbed it, hardened a pattern that now defines the 2026 bull market: a handful of artificial-intelligence and semiconductor names doing nearly all the work. The S&P 500 closed at a record on the last trading day of May, but only 20 of its members hit their own all-time highs that session, and just seven of those were not directly tied to AI. Whether that concentration is the start of something or the end of it is the question dividing strategists as the second half of the year opens.

What Son committed

SoftBank's French program will deliver 3.1 gigawatts of data center capacity in the northern Hauts-de-France region by 2031, with sites in Dunkirk, Bosquel and Bouchain, the company said in a statement issued Sunday and confirmed at Monday's press briefing with Macron. The initial five-year spend is 45 billion euros, or about $53 billion. SoftBank will partner with French engineering firm Schneider Electric on an industrial production cluster in Dunkirk. Son told reporters the full system, taken in aggregate, is closer to $750 billion. SoftBank's own Sunday statement flagged Europe's high energy costs as a stumbling block for the region's AI ambitions, noting prices are surging amid the U.S.-Iran war and that data-center projects are likely to migrate to parts of Europe with cheaper power.

"It's a massive size of investment coming," Son said at the briefing. "We are doing that in the U.S. already, we are expanding a lot in the U.S., so we have the momentum, which we can make France the center of Europe, and Europe needs this kind of AI technology."

The SoftBank chief said the company will lean on project financing rather than its own balance sheet, pointing to a 10-gigawatt project in Ohio that he said will soon secure long-term take-off agreements with hyperscaler customers. "Our own money that we need is very, very condensed," he said.

On the Street

The rally underneath the announcement has been narrow and chip-shaped. Memory makers Micron Technology, Advanced Micro Devices, SK Hynix and Samsung — each now valued at or near a trillion dollars — drove most of May's gain. AMD rose 50 percent on the month. Micron jumped 85 percent. Samsung added 43 percent. SK Hynix climbed 81 percent. The Nasdaq's two-month run is the index's strongest since the early 2000s.

Son, speaking to CNBC's Arjun Kharpal in Paris on Monday, framed the buildout as the early phase of something larger than the last technology cycle. "I think this is like more than 10x, probably 50x bigger than dot-com," he said. He added: "This is the biggest revolution of technology and realization that mankind ever experienced, so this is just like the beginning of the internet." Referencing the auto and electronics stocks that crashed in 1929 and then ground higher for decades, Son said, "There's always a correction."

The dot-com parallel

That is precisely the parallel a growing number of Wall Street strategists are now drawing — though not in the direction Son intends. Michael Hartnett, the Bank of America strategist, told clients in a note at the close of last week that exactly 20 stocks hit new highs at the very top of the internet bubble in March 2000, the same count as Friday. Hartnett said the "speculative price action" is likely not over, but called the narrowing a late-stage signal and is advising clients to prepare to flip defensive. His post-bubble roadmap, he wrote, is "long bonds, and long combo of defensives and/or sectors which dramatically underperformed in the last months of the bubble."

Other desks point to the same internal weakness. Only about 55 percent of S&P 500 constituents were trading above their 200-day moving average as of May 20, according to BCA Research. Strategists led by Arthur Budaghyan wrote in a May 20 note that "Poor breadth is often a sign of underlying stock market vulnerability." Oppenheimer's Ari Wald, in a May 23 technical note, wrote that "Internals have lagged since the initial April surge."

The counterpoint

Today's reporting on the cluster sits entirely in center-of-the-dial business outlets, and the substantive bearish view comes from inside that bucket rather than from a partisan one. Hartnett's note, the BCA breadth work and the Oppenheimer read converge on one warning: the market that lifted SoftBank past Toyota is carried by the same number of stocks that carried it to the March 2000 peak. Son's counter — that 1929's auto-and-electronics crash gave way to a century of gains — is a long-run argument that does not preclude a near-term drawdown of the kind Hartnett is preparing clients for.

SoftBank reports fiscal first-quarter results in August, when investors will get their first read on whether the project-finance model Son outlined Monday can fund the French and Ohio buildouts without dragging on the parent balance sheet.