AI Investments Key for SoftBank Shares After $65 Billion Rally

After adding more than $65 billion in market value over the past four months, the fate of SoftBank Group Corp. shares is more firmly attached to the global artificial intelligence boom than ever before.

Investors are returning to Masayoshi Son’s flagship company thanks to its key position in Donald Trump’s AI strategy, stake in OpenAI and growing holdings in major names such as Nvidia Corp. These will hold more sway over SoftBank’s stock than tariffs, geopolitics or even the company’s upcoming earnings report.

Short bets on the company stand at less than half the recent peak level, and forward ...