Babylon Health, the U.K.-based startup that has developed a number of AI-based health services, including a chatbot used by the U.K’.s National Health Service to help diagnose ailments, has confirmed a massive investment that it plans to use to expand its business to the U.S. and Asia, and expand its R&D to diagnose more serious, chronic conditions. It has closed a $550 million round of funding, valuing Babylon Health at more than $2 billion, it announced today.

This is the largest-ever fundraise in Europe or U.S. for digital health delivery, Babylon said.

“Our mission at Babylon is to put accessible and affordable healthcare into the hands of everyone on earth,” said Dr Ali Parsa, founder and CEO of Babylon, in a statement. “This investment will allow us to maximise the number of lives we touch across the world. We have a long way to go and a lot still to deliver. We are grateful to our investors, our partners and 1,500 brilliant Babylonians for allowing us to forge ahead with our mission. Chronic conditions are an increasing burden to affordability of healthcare across the globe. Our technology provides a solid base for a comprehensive solution and our scientists, engineers, and clinicians are excited to work on it. We have seen significant demand from partners across the US and Asia. While the burden of healthcare is global, the solutions have to be localised to meet the specific needs and culture of each country.”

Before today’s announcement, the investment — a Series C — had been the subject of a lot of leaks, with reports over recent days suggesting the investment was anywhere between $100 million and $500 million.

The round brings together a number of strategic and financial investors, including PIF (Saudi Arabia’s Public Investment Fund); a large U.S.-based health insurance company (which reports suggest to be Centene Corporation, although Babylon is not disclosing the name); Munich Re’s ERGO Fund; and returning investors Kinnevik and Vostok New Ventures. (Previous investors who do not appear to be in this round also include Demis Hassabis, the AI expert who co-founded DeepMind, which is now a part of Google.)

This is a big leap for the company, which had raised more modest rounds in the past, such as $60 million investment three years ago (it had only raised about £72 million in total prior to this round). Babylon said that of this latest Series C, $450 million has been secured already, with another $50 million agreed to be exercised at a later date, and the remainder getting closed “shortly.” (The PIF has been a prolific, if controversial, investor in a number of huge startups, such as Uber, and wider investment vehicles like SoftBank’s Vision Fund.)

We’re at a moment right now when it seems like a daily occurrence that a new company or service launches using AI to advance health. (Among that group, competitors to Babylon Health include MDLive, HealthTap, Push Doctor and many more.)

But even within that bigger trend, Babylon has emerged as one of the key players. In addition to its work in the U.K. — which includes an NHS service that it offers to “take over” a user’s local GP relationship to diagnose minor ailments remotely, as well as a second-track Babylon Private paid tier that it’s built in partnership with private insurer Bupa — it says other partners include Prudential, Samsung and Telus.

The NHS deal is an interesting one: The state’s health service is thought of by many as a national treasure, but it’s been very hard hit by budget problems, the strain of an ageing and growing population and what seems sometimes like a slow-release effort to remove some of its most important and reliable services and bring more privitisation into the mix.

Bringing in AI-based services that remove some of the overhead of people managing problems that machines can do just as well is one way of taking some of that pressure off the system — or so the logic goes, at least. The idea is that by handling some of the smaller issues, it helps prioritise the more urgent and difficult problems for people and face-to-face meetings.

That additionally gives Babylon (and others in digital health) a big opportunity to break down some of the more persistent problems in healthcare, such as providing services in developing economies and remote regions: one of its big efforts alongside rollouts in mature markets like the U.K. and Canada has been a service in Rwanda to bring health services to digital platforms for the first time.

Babylon has been growing and says it delivers 4,000 clinical consultations each day, or one patient interaction every 10 seconds. It says that it now covers 4.3 million people worldwide, with more than 1.2 million digital consultations completed to date, with more than 160,000 five-star ratings for appointments.

That is the kind of size and potential that has interested investors.