Specialized tech skills are more important to earning your full potential than ever before, according to new data.

In February, we highlighted how tech skills were quickly becoming the new way for developers and engineers to earn more. Our annual Salary Survey showed some plateauing for average tech income; the average tech salary hasn’t shown significant change since 2015. If you want to make more money, you need to specialize in what the market wants.

Upwork recently released a quarterly index of the hottest skills for the freelance job market, showing which are most in-demand on its platform. The company claims its findings provide “real-time validation of current trends in the labor market and tech industry,” which we’re inclined to trust it. The freelancing market typically has considerable urgency, as companies and clients pushing into new areas of emerging tech need qualified help as quickly as possible.

This may be why some upstart skills show such earning potential. We took Upwork’s findings and compared it to our own salary data to see which of the more popular skills (via Upwork) will actually get tech pros paid. We simply passed the listed skill through our database, which returns an average salary.

Some skills didn’t make the cut. Volusion, Google App Engine API, and GitLab were notable exclusions on the Venn diagram between Upwork and Dice. Others required substitutions; for ‘Go Development,’ we chose any development role with ‘Go’ in the title, and ‘iOS Architect’ was substituted for ‘UIKit.’ For ‘articulate storyline,’ we searched for ‘business development manager’ in the Dice database, as that’s a key role that requires telling narratives to teams. All of the following numbers are, obviously, in U.S. dollars.

TensorFlow is currently the highest-paying tech skill. Tech pros adept at TensorFlow earn roughly $160,478 on average. The ever-volatile blockchain also ranks highly, with an average pull of $152,533.

(If you’re looking at these figures and wondering why the findings don’t match your earnings, keep in mind we’re only parsing skills. This doesn’t account for experience, job title, or geography, among other considerations which may skew actual salaries one way or another.)

There are a few key takeaways, too. TensorFlow shows machine learning is a skill many companies are looking for, and willing to invest in. Blockchain’s inclusion here is a good indication it’s a technology companies are taking a good look at, though it may be riding on the coattails of cryptocurrency.

We also see a strong pull towards Apple’s ecosystem. UIKit and Xcode both pay well, and technologies such as TensorFlow and blockchain both work well with Swift. Apple is also getting serious about server-side Swift with SwiftNIO, and has its own machine-learning stacks with CoreML and Create ML. Even the node.js crowd wants in on Swift! If you’re interested in making a career shift or learning a new language, Swift may be the best choice.

Machine learning is a smart bet on the future of tech. So is Swift. We’re still on the fence about blockchain; we know you love it, but we need to see blockchain applied more broadly before we’re ready to sing its praises. Luckily, most of this list is composed of staid, reliable skills worth learning if you haven’t mastered them yet.