American Airlines, like most large companies, has legacy applications to manage tasks and will move some of them to IBM’s (IBM) public cloud and use IBM’s BlueMix tools to modernize them. It did not specify which applications would move.

“The agreement runs the gamut from software and services to infrastructure and also will include data analytics and Watson going forward,” said Patrick Grubbs, IBM’s vice president of travel and transportation. “Watson” is IBM’s brand of artificial intelligence software that is being customized to suit various vertical industries.

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Neither he nor an American Airlines (AAL) spokeswoman would put a dollar figure on the deal, which is not exclusive. In a prepared statement, the airline said that the cloud computing model, which lets companies add and delete resources as needed, will give it more flexibility and scale for some of its business software.

In September, American’s chief information officer Maya Leibman told the CIO Journal that the airline was evaluating a move to the cloud and expected to make decisions about it within months. This looks to be one of those decisions. The American Airlines statement noted that IBM was “a cloud partner,” so there is no exclusivity implied.

Asked about that point, an airlines spokeswoman stressed that it is a big company that works with lots of tech providers. “We use the best and newest tools for the right applications,” she told Fortune. And, since this is new technology, there will be a lot of testing before it goes live.

The airline is not alone in this massive technology shift. Most large companies are weighing the need to keep building and operating their own data centers or moving more of those computing and data storage jobs to a third-party cloud provider like Amazon (AMZN) Web Services, Microsoft (MSFT) Azure, Google (GOOGL) Cloud Platform, or IBM SoftLayer.

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There will be more discussion about companies moving to the cloud at Amazon’s annual AWS Re:invent conference this week in Las Vegas, where Amazon will undoubtedly claim a list of customer wins. But while AWS is by far the largest public cloud purveyor, it doesn’t have this market to itself anymore. Microsoft, Google, VMware (VMW), IBM, and others are all wooing enterprise customers with their respective public clouds.

It probably doesn’t hurt that IBM and American have a relationship going back decades. IBM, for example, worked with American Airlines on SABRE, the pioneering online reservation system.