Anthropic has issued a direct warning to investors that several private and secondary investment platforms are not authorized to buy or sell its shares. The company named eight firms — including Open Doors Partners, Unicorns Exchange, Pachamama Capital, and Forge Global — stating that any stock sold through them is void and will not be recognized on its books.

Forge Global told TechCrunch it was included erroneously and is working with Anthropic to have its name removed. The warning arrives as investor appetite for AI company shares has surged dramatically. Anthropic, rumored to be raising fresh funding at a $900 billion valuation, has become one of the hardest private stocks to source on secondary markets, according to brokers.

Unauthorized offerings have taken multiple forms, including special purpose vehicles that hold equity stakes, tokenized securities, and pre-IPO perpetual futures contracts that track private company valuations without granting actual ownership. Anthropic emphasized that both its preferred and common shares carry transfer restrictions, making any unapproved sale or transfer invalid.

For investors chasing exposure to Anthropic's growth, the company has drawn a firm line. Any transaction that bypasses its transfer restrictions — whether through SPVs, retail platforms, or derivative instruments — will not be honored. That leaves buyers holding stakes the company itself may refuse to recognize.