Last May, Anthropic, one of the world’s hottest artificial intelligence start-ups, raised $450 million from investors including Google and Salesforce. It was the beginning of an astonishing funding spree.

By August, Anthropic had landed $100 million from two Asian telecoms. Then Amazon committed $4 billion to it, followed by $2 billion more from Google.

This month, the venture capital firm Menlo Ventures closed a deal to invest $750 million in Anthropic.

All told, the A.I. start-up hauled in $7.3 billion in a year. Its five funding deals stood out not just for their speed and size, but for their unusual structures.

In one of those deals, Anthropic agreed to use technology such as chips and cloud computing services from the companies that invested in it. That meant, in effect, that some of the money it raised would be pumped back into its investors. And to consolidate smaller investors who were interested in Anthropic, Menlo created a legal entity known as a “special purpose vehicle.”

“These deals are so complicated,” said Dave Brown, an Amazon Web Services vice president who was involved in Amazon’s deal with Anthropic.