Duolingo is one of the clearest examples of freemium done right. Tens of millions of daily users. A massive free experience. And a subscription business that generates the vast majority of its revenue—without gutting what made the product valuable in the first place.
In this episode of Sub Club, Cem Kansu—former VP of Product at Duolingo—walks through the decisions, trade-offs, and hard calls behind that balance. What stands out isn’t a clever pricing trick or a perfectly tuned paywall. It’s a philosophy: protect the free experience, even when short-term revenue is tempting.
Here are the core lessons every subscription app builder can take from Duolingo’s journey.
Protect the free moat—always
One of the biggest traps in freemium is also the easiest win: take something free, make it paid, and watch revenue spike.
Cem has seen this play out repeatedly—and warns it rarely works long-term.
At Duolingo, the free experience wasn’t just a funnel. It was the product’s moat. Locking too much behind a paywall might boost metrics for six months, maybe a year. But it weakens the growth engine and creates space for competitors to offer what you just took away.
Free value isn’t charity. It’s strategy.
Duolingo’s early success came from doing something incumbents wouldn’t: offering high-quality language learning completely free. Undoing that advantage would have meant undoing the company’s differentiation. So instead of extracting more from free users, the team focused on preserving—and often expanding—the free experience, even when it meant saying no to revenue-positive ideas.
Freemium isn’t a trade-off—it’s the growth engine
At Duolingo, free users were never treated as freeloaders. They were the primary distribution channel.
Word of mouth fueled growth, and word of mouth only worked if the free product delighted people. When free users learned more, progressed faster, and felt respected, they told their friends. That loop compounded.
This is why Duolingo was willing to do something that feels counterintuitive to many subscription teams: move features from paid back to free.
When features like Practice Hub or “Explain my answer” didn’t justify their revenue impact—or became cheaper to run thanks to AI efficiency—the team intentionally took a revenue hit to strengthen the free experience. The short-term numbers dipped. The long-term growth engine got stronger.
That trade-off only makes sense if you believe free users are part of your business, not a cost center.
Monetize with empathy, not extraction
Introducing monetization to a previously free product is as much a cultural shift as a product one.
When Duolingo added ads, the team expected backlash—and they got some. But instead of reacting emotionally to negative reviews, they zoomed out. They measured everything: retention, app closes, review volume per million DAUs, complaint rates across different issues.
What they found was grounding. Ads created noise, but they didn’t meaningfully damage the core experience when done carefully.
The rule was simple: optimize for trust, not ARPU.
Ads only appeared after a lesson—never before, never during. Categories that felt off-brand or unsafe were blocked, even if it cost revenue. Over time, Duolingo went further, partnering directly with advertisers to create custom ad formats that fit the product’s tone and even extended its character-driven world.
The goal wasn’t to squeeze users harder. It was to monetize in ways that felt fair, predictable, and respectful.
A/B test relentlessly—but know when to ignore the data
Duolingo runs hundreds of experiments at any given time. Testing is foundational to how the product evolves.
But Cem is clear: experimentation isn’t the same as outsourcing judgment to dashboards.
Many tests surface uncomfortable trade-offs—revenue up, learning quality down; engagement up, trust eroding slowly. In those moments, the job of product leadership isn’t to follow the green line. It’s to decide whether the result aligns with the company’s long-term goals.
Some of Duolingo’s most important decisions required taking a measurable loss: lower revenue, lower short-term engagement, worse-looking graphs. Those calls often needed senior buy-in because the upside—stronger learning, deeper trust, long-term growth—couldn’t be fully captured by a single metric.
Data informs decisions. It doesn’t make them.
Ads can be strategic—and even creative
Duolingo didn’t just “add ads.” It treated ads as part of the product experience.
Placement mattered. Timing mattered. Quality mattered.
Ads only appeared at natural breaks, never interrupting learning. Programmatic categories were aggressively filtered. And increasingly, Duolingo shifted toward direct brand partnerships, embedding its own characters into ads to make them feel less jarring and more native.
Internally, ads weren’t just monetization. They were another surface to reinforce brand, tone, and user expectations—while still funding free education at scale.
Build for everyone, not a persona
One of Cem’s most contrarian takes: personas are often a liability at scale.
Language learners don’t fit clean buckets. People learn for work, for travel, for family, for identity, for fun. Optimizing for a single “core persona” risks alienating the long tail that actually drives growth.
Instead of narrowing the audience, Duolingo built systems flexible enough to serve wildly different motivations—without forcing users into rigid paths. That inclusivity is part of how the product scaled from millions to tens of millions of users without fragmenting.
The throughline: take the long view
Across monetization, experimentation, ads, subscriptions, and AI, Duolingo followed a consistent principle: build the company you want to exist in 100 years, not the one that looks best this quarter.
That mindset made some decisions harder. It meant leaving money on the table. It meant resisting obvious optimizations. But it also built trust, sustained growth, and a freemium model that didn’t collapse under its own incentives.
For subscription app builders, the lesson is clear:
If you burn your free moat, you burn your future.
🎧 Listen to the full Sub Club episode with Cem Kansu to hear the stories, experiments, and trade-offs behind Duolingo’s monetization journey—straight from the person who led it.