SoftBank Group Corp. (SFTBY) CEO Masayoshi Son had a brutal Tuesday, watching $4.9 billion disappear from his personal fortune as investors grew increasingly nervous about his big bet on artificial intelligence. The wealth evaporation sent the Japanese billionaire tumbling to 32nd place on Forbes' Real-Time Billionaires list.

From Third to Eighth in Asia's Wealth Rankings

Son's net worth now sits at $49.3 billion, a dramatic comedown from his position as Asia's third-richest person just a few weeks ago at the start of the month. He's now ranked eighth among Asian billionaires, slipping just below Uniqlo CEO Tadashi Yanai.

The damage stems from SoftBank's stock hitting its lowest point since mid-September. Shares crashed nearly 11% on Tuesday in Tokyo, following an already painful 10.9% drop the previous Friday. Over the past month alone, the stock has plummeted 36.16%. That's the kind of decline that makes even billionaires wince.

Google's Gemini 3 Rattles SoftBank's AI Strategy

The timing tells the story. Investors are getting worried about mounting competition for OpenAI, a cornerstone investment of SoftBank's Vision Fund. And what's fueling those worries? Google (GOOGL) just rolled out its new Gemini 3 AI model, which CEO Sundar Pichai described on November 18 as the company's most advanced and context-aware AI yet. Google is touting major improvements in multimodal and agentic capabilities as it steps up its rivalry with OpenAI, calling Gemini 3 its most intelligent model that can help bring ideas to life.

The stock slump reflects broader anxiety about artificial intelligence and which companies will actually dominate the space. Son has been going all-in on AI, and the market is now questioning whether that strategy will work out. Earlier this month, SoftBank sold off its stakes in T-Mobile US Inc. (TMUS) and Nvidia Corp (NVDA) specifically to fund massive AI investments, including a significant commitment to OpenAI.

Antitrust Concerns Loom Over Stargate Project

Adding to the complexity, a Yale Law School researcher recently raised concerns about potential antitrust issues surrounding the Stargate Project, a joint AI infrastructure initiative involving OpenAI, SoftBank, and Oracle Corp (ORCL). The initiative has backing from the Trump administration, but it's also raising questions about whether too much power is consolidating among a handful of major AI players.

For Son, the question now is whether his massive AI bet will eventually pay off, or if competitors like Google will eat away at OpenAI's lead before that happens. Tuesday's stock performance suggests investors are getting more skeptical about the answer.