CNBC reported in February that the company was finalizing a $40 billion investment in the Sam Altman-run startup at a $260 billion pre-money valuation.
The investment takes SoftBank's stake in the company above 10%.
The Japanese investment giant sent over a final $22 billion to $22.5 billion last week, according to the sources familiar with the matter. SoftBank had previously syndicated $10 billion and invested $8 billion in the ChatGPT maker.
At the time, sources told Faber that the funding would be paid out over a 12 to 24 month period. Some money was slated to support OpenAI's artificial intelligence infrastructure Stargate joint venture with Oracle and SoftBank.
Companies have been spending big in recent months to build out infrastructure to support a frenzy for AI solutions and growing compute needs.
OpenAI has made more than $1.4 trillion in infrastructure commitments over the next several years, including agreements with chipmakers Nvidia, Advanced Micro Devices and Broadcom.
Over the years, SoftBank has been betting big on technology and AI companies and was an early investor in chipmaking giant Nvidia. On Monday, the conglomerate agreed to pay $4 billion for data center investment firm DigitalBridge to strengthen its AI push.
Last month, SoftBank liquidated its entire $5.8 billion stake in major AI beneficiary and chipmaker Nvidia . A source familiar with the matter told CNBC that the sale, combined with other cash sources, would support its OpenAI investment.
The startup, which is reportedly preparing for an IPO, has received billions in funding over the years from tech juggernaut Microsoft .
Earlier this month, CNBC reported that OpenAI was exploring a potential more than $10 billion investment from Amazon . Disney made a $1 billion equity investment that allows users to generate content with characters such as Mickey Mouse.