Why is SoftBank stock declining today?

SoftBank's stock experienced a decline of 2.3% on Tuesday, reaching ¥6,349, continuing a period of weakness that began after the company completed its $30 billion investment in OpenAI on October 1. The accumulation of this investment, amounting to $64.6 billion, now makes SoftBank the 13% owner of the AI startup. Following the successful completion of the third and final tranche of its follow-on investment in OpenAI, investors have shifted to a "sell the news" stance, questioning whether the returns from this massive commitment can justify the leverage required to fund it.

This week, SoftBank's most valuable publicly traded asset faced a fresh headwind, as Qualcomm and Arm Holdings commenced a trial on October 5, 2026, with Qualcomm alleging that Arm withheld necessary testing tools and leaked information regarding a critical license agreement cancellation threat. As SoftBank holds approximately 87% of Arm, any legal or reputational damage to Arm’s licensing franchise directly impacts SoftBank's net asset value, further exacerbating existing concerns.

Additionally, SoftBank's credit default swaps surged to their highest levels since 2023, indicating bond market anxiety over the conglomerate's aggressive leverage strategy to finance its AI investments. The broader Japanese market offered little respite, with Tokyo stocks displaying muted performance due to profit-taking following the previous day's surge.

AI- and semiconductor-related shares led the selling activity after their recent substantial gains. As a Nikkei 225 heavy hitter with significant exposure to the AI sector, SoftBank has been disproportionately affected by this market rotation.