By Joseph Pisani

$Amazon (AMZN.US)$ said it has invested an additional $2.75 billion in the artificial-intelligence startup Anthropic, a major investment from a tech giant looking to compete with $Microsoft (MSFT.US)$, $Alphabet-A (GOOGL.US)$ and others in the AI arms race.

Amazon has now invested a total of $4 billion in Anthropic after making a $1.25 billion initial investment in the company in September. Amazon said it has a minority ownership position in Anthropic.

The funding marks Amazon's largest investment in another company since the online retailer was founded nearly 30 years ago. Google agreed last October to invest up to $2 billion in Anthropic.

Tech companies and venture capitalists have been throwing money at AI startups following the success of Open AI's ChatGPT, with investors and analysts increasingly believing the latest boom in AI is sustainable. More than $29 billion was invested in generative AI companies last year, according to research firm PitchBook. Microsoft has agreed to invest $13 billion in OpenAI.

Anthropic, which was founded in 2021, offers an AI assistant called Claude that competes with OpenAI's ChatGPT. The company is led by siblings Dario and Daniela Amodei, who both used to work at OpenAI.

Write to Joseph Pisani at joseph.pisani@wsj.com