Anthropic, the OpenAI rival founded by ex-OpenAI employees, is in talks to raise a $750 million funding round led by Menlo Ventures, a person with direct knowledge of the matter told CNBC.

The round would value Anthropic at up to $18.4 billion, per the source familiar — nearly 4.5x the startup’s $4.1 billion valuation earlier this year.

News of the fundraise was previously reported by The Information. Anthropic declined to offer a comment for this story.

Founded in 2021 and funded by companies including Google, Salesforce and Zoom, Anthropic had already raised a combined $750 million from two funding rounds in April and May — one of which involved Google taking a 10% stake in the company. Anthropic’s May fundraise marked, at the time, the largest AI company funding round since Microsoft’s investment in OpenAI in January, according to PitchBook data.

In October, Google agreed to invest up to $2 billion in the startup — a commitment involving a $500 million upfront cash infusion and an additional $1.5 billion to be invested over time.

Anthropic is the developer of Claude 2, a rival chatbot to OpenAI’s ChatGPT that is used by companies including Salesforce-owned Slack, Notion and Quora. Claude 2 has the ability to summarize up to about 75,000 words, which could be the length of a book. Users can input large data sets and ask for summaries in the form of a memo, letter or story. ChatGPT, by contrast, can handle about 3,000 words.

Anthropic was founded by Dario Amodei, OpenAI’s former vice president of research, and his sister, Daniela Amodei, who was OpenAI’s vice president of safety and policy. Several other OpenAI research alumni were also on Anthropic’s founding team.

Research by Arthur AI, a machine learning monitoring platform, tested chatbots from Anthropic, Meta, Cohere and OpenAI and found Claude 2 to be most reliable chatbot in terms of “self-awareness,” meaning accurately gauging what it does and doesn’t know, and answering only questions it had training data to support.

Daniela Amodei told CNBC in July that Anthropic invested at least two months in developing its newest chatbot, with a team of 30 to 35 people working directly on the AI model and a total of 150 people supporting it. She said the market is growing so rapidly that there’s plenty of room for multiple players to succeed.

“It’s a really unusual time from a business perspective because there’s just so much demand for large language models and really more demand than the industry can currently provide,” Amodei said at the time. “The landscape is just very wide, and there’s really quite a lot of room for many different users and types of users to make use of these systems.”