According to Charles Hoskinson's response in a recent AMA, Cardano spent approximately 1,090 BTC raised during its 2016 crowdsale on audit fees related to the project's token sale. The bitcoins were originally valued at $454,000 at the time of payment.
The disclosure follows investor Thomas Braziel's public questioning about the whereabouts of the BTC, which is now worth around $70 million. Braziel has requested Hoskinson provide documentation including invoices, agreements, approvals, and payment records to verify the stated use of funds.