Sam Altman secretly owned way more Reddit stock than we thought

• As Reddit prepares to go public, a new filing with the SEC has revealed its biggest backers.
• OpenAI's Sam Altman is the third-largest shareholder, the filing revealed.

We learned a new detail about Sam Altman Thursday: just how much he supports Reddit.

In preparation for its highly-anticipated IPO, the online social forum filed an S-1 form with the Securities and Exchange Commission on Thursday, detailing the company's financial background. The filing revealed that Altman, the CEO of OpenAI, owns an 8.7% stake in the company.

Altman was previously known to be an investor in Reddit, though exactly how much he owned has not been disclosed until now — the company has to share that now since it intends to go public. And turns out he is the third-largest shareholder in the social networking site. Altman controls 8.7% of the company's stock, according to the filing.

He comes behind Advance, owned by the Newhouse family, which owns 30% of the company, while Chinese company Tencent has an 11% stake.

Altman also served seven years on Reddit's board until 2022.

Reddit is the first social media company to submit an initial public offering since Pinterest in 2019, and it's the first major tech company to file for an IPO in 2024.

While the company reported a 20% rise in revenue last year compared to the year before, it still struggled to turn a profit, according to the filings.

However, AI may be a key revenue source for Reddit. On Thursday, Reddit announced that it has entered into a data licensing agreement with Google. The search engine company will pay the company $60 million a year for access to its content.

Reddit doesn't currently have a data licensing deal with OpenAI, though.

"Reddit's vast and unmatched archive of real, timely, and relevant human conversation on literally any topic is an invaluable dataset for a variety of purposes, including search, AI training, and research," Reddit cofounder Steve Huffman wrote in a letter attached to Thursday's SEC filing.

"We expect our data advantage and intellectual property to continue to be a key element in the training of future LLMs," he wrote, referring to large language models, a type of program used by AI systems like Altman's ChatGPT.

The concept of working this closely with AI companies hasn't gone over great with some Reddit users, who have criticized the idea of profiting off users' data without their consent.

Reddit wouldn't be the only social media company to let AI companies tap into users' conversations. Elon Musk's new AI chatbot, Grok, is trained on X user data.