Duolingo has been through a lot of changes over the past few years. What was once solely a language-learning app has grown into a social media marketing machine, a destination for math and music lessons, and now an online chess tutor.

In June, Duolingo launched a Duolingo Chess course to teach beginners the basic rules and moves by allowing them to play against an AI tutor named Oscar. This month, the company is taking the course further, launching a multiplayer version of the game where users can compete against one another. 

Duolingo, which is on track to surpass $1 billion in revenue this year, has 48 million daily active users and 11 million paying subscribers. Though the company doesn’t reveal user numbers for the free chess course, at the Fast Company Innovation Festival in September, cofounder and CEO Luis von Ahn said that it had already notched “millions and millions of users” within three months. 

Even more remarkable: Von Ahn greenlit the development of the chess course only nine months before it launched. 

The story of how Duolingo created its hit chess course is the clearest illustration of how AI is transforming the company. Fast Company spoke with two of the principals behind the chess course. As they make clear, AI is not replacing engineers, but it is giving them a head start. Vibe coding has become a phenomenon, but we don’t have any high-profile examples of a hit product that relied on it. Until now. 

Chess as education

Von Ahn admits to being skeptical about offering chess lessons when the idea was first pitched to him a couple of years ago. He didn’t want Duolingo to turn into an app for games. But a conversation with Guatemala’s minister of education changed his mind. (Von Ahn was born and raised in Guatemala.) The minister was so frustrated with the education system in her country that she said she was thinking about sending every student a chess board so that at least they’d learn how to play. That helped von Ahn see the game through an educational lens. 

He greenlit the idea and handed it to the pair of employees who initially pitched it: “Neither of them knew how to play chess, and neither of them were engineers,” von Ahn says. But they didn’t need those skills to get started. They simply vibe coded a prototype.

AI has been an important part of Duolingo’s workflow strategy. Earlier this spring, von Ahn sent a memo to his staff outlining plans to make Duolingo an AI-first company to remove bottlenecks and inspire employees to focus on creative work and real problems rather than repetitive tasks. The memo sparked a backlash. On social media, people accused von Ahn of using AI to eliminate jobs. 

At Fast Company’s Innovation Festival, von Ahn cleared the air, saying that the goal isn’t to save money. “We have never done a layoff. We have not laid off a single full-time employee,” he said. “The goal is not to replace human employees. The goal is to do a lot more and get closer to our mission.” 

How to vibe code the game of chess

The development of Duolingo’s chess course kicked off in September 2024 with Edwin Bodge, senior staff product manager, and Tyler Murphy, Duolingo’s chief product designer.

Bodge and Murphy, who had worked together to launch the math and music products for Duolingo, had grown interested in chess when they were brainstorming ideas for a strong third subject. They saw the correlation between learning chess and language learning. 

To begin the prototyping, they tried a combination of products, including the popular AI-generated coding platform Cursor. Using Cursor, they created an initial version of the chess experience.

Bodge says the first steps in prototyping were relatively easy. They began by describing a chess board on the Cursor platform, then added other elements, such as a character (which eventually became the AI tutor, Oscar), a progress bar, and the actual lessons and puzzles. 

But as Bodge and Murphy layered on more curriculum, things became much more complicated. They started to have a difficult time visualizing the course, so Bodge created multiple chess boards on Cursor to play through each version of the prototype. Soon, they had something fully formed enough to show to colleagues.

“It was a pretty janky prototype,” Bodge admits. “But we were able to put it into people’s hands and say, ‘Well, here’s the curriculum we’ve been writing. Here’s all this stuff that we’ve been teaching and how we think it’s going to work.’ And from that moment, it just became so much more natural.”

Bodge notes that there are still some aspects of the prototype that are incorporated into the final product, including the curriculum and some of the AI-generated code that he and Murphy developed. “That core of the vibe code and prototype is very much in the production app,” he says.

Building the final product

Within a few months, Bodge and Murphy began handing off the project to Duolingo engineers to create the code that would bring the course to life. Sammi Siegel, staff software engineer, was instrumental in building the final product.

Thanks to the prototypes that Bodge and Murphy had developed, “there was a pretty strong vision for what [the course] should look like,” Siegel says. “The first few months were implementation, heads down, and coding everything all at once.”

Siegel says the chess game was the first time the team had launched a new subject within the existing Duolingo app. (The math and music classes were built to be stand-alone apps, and then eventually merged into Duolingo.) “We were building [a course] within the current system, so we were able to prove how much faster that [process] was,” Siegel explains. 

Siegel’s team was also helped by the amount of open-source work that exists around chess. She and her team were able to take advantage of publicly available chess engines, which analyze chess positions and the best moves.

And then there’s the visual simplicity of chess. “Chess is pretty simple,” Siegel says. “It’s just a board and a guy telling you what he wants you to do on the board, so that made the implementation phase shorter. We were able to get a lot further with a very simple interface.” (To build the chessboard, Siegel says the team used a software called Rive, which is cross-platform compatible and can be built in one go for iOS and Android.)

Duolingo released the course in beta in April and launched it to the public in June. Now it’s ready for the next step: introducing player-versus-player mode, which entails a complex coding process.

Siegel says creating real-life, player-versus-player functionality is tougher than building matches against a predictable bot, like Oscar. “You’re coordinating two humans who think, pause, and play at their own pace,” she explains. “With Oscar, we can guarantee that you’ll get matched with a bot that’s pretty close to your skill level.” 

Siegel adds that keeping both devices in sync is “a challenging engineering problem,” noting, “We’ve had to invest in anti-cheating systems and thoughtful handling of disconnections to ensure every match feels fair and stable.”

A new generation of online chess players

By incorporating chess into Duolingo, the company is introducing the game to people who may have never considered learning it before. “We talk internally about chess as a very male-dominated game, so it’s interesting to see how we can widen the scope of folks who have access to that kind of education,” Siegel says.

Bodge says when they first started developing the product, they had a hypothesis that it would appeal to a lot of people. But they wanted to make sure that it felt accessible and engaging, rather than elite and academic. That’s why, in classic Duolingo style, they use an animated character—Oscar—to play the role of the easygoing tutor. 

“There are a lot of people who we’ve basically activated as chess players,” Bodge says. “We’re ushering in a new generation of players.”

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