Millions of learners “keep their streak alive” every day on Duolingo. It’s one of our most iconic features and a daily reminder that language learning is a long game, but one you can play for just a few minutes a day (every day). And the streak is an effective learning tool—our data shows that the streak helps motivate learners to keep on keepin’ on with their daily practice.

One of the most rewarding moments in a learner’s streak is a “milestone” day—hitting a notable number of consecutive days learning. These are exciting moments, but did they feel exciting enough to the learner? Reaching a one week, one month, 100 day, or one year streak and beyond on Duolingo is no small feat and should be celebrated! So, we tapped our talented design team and found three key areas where we could improve the Duolingo streak experience, and make sure learners everywhere felt excited about their accomplishments!

Step one: make the streak universal

Though many learners love their streak, our research and focus group studies revealed that some learners new to Duolingo don’t understand the streak when beginning their language journey. Why? One hypothesis: the analogy of “keeping the flame alive” or being “on fire” when you’ve got a rally going is not shared by all cultures across the globe. We want one of our most popular features to be as universally understood as possible, and our old design wasn’t quite there.

Sketches of the Duo owl interacting with flames in different ways. In one images, he's roasting a s'more, in another he's carrying a candle, in another he's working with a science lab beaker over an open flame.

Though these ideas were fun to sketch, we worried they weren’t scaleable and still missed the “universality” that we were looking for

Then, we had a different idea: what if we treated milestones like “power ups” in a video game, and Duo himself physically changed on these exciting days? This instantly resonated with everyone on the team, but the hardest part was getting “Fire Duo” to look right.

After many different iterations, we leaned on the mythical phoenix, a well-known image across cultures. Many flags and cultures have used the image of a bird in profile in their nations flags (think: the Official Seal of the President of the United States or the coat of arms of Germany), so we felt this image was clear and powerful, and allowed us to maintain the fire metaphor in a more accessible way.

Three versions of the Duolingo Owl becoming a rising phoenix with a flame surrounding him.

Variations on a theme: Exploratory Phoenix Duo Designs.

Next: make the streak celebratory

Now that we had a more widely-understood image, our design needed to lean into that excitement, and give learners something to look forward to as they practiced for more days. The previous version had Duo holding number balloons. Cute, but not quite celebratory enough, energy-wise. We saw an opportunity to improve upon this! With the phoenix imagery, we could animate milestones that were much more exciting and powerful.

Duolingo Owl carrying balloons in the shape of the milestone the learner reached: 50 days, 100 days, 365 days.

The original balloon version of our streak milestone art.

Timing is everything in animation. Multiple passes of rough animation are done to experiment with different variations on an idea before refining the overall rhythm and energy. These variables are as important to the success of Duo’s transformation as the design itself.

Eventually, the final animation begins to take form (er, flight?) and it all starts to come together. This is perhaps the most rewarding part of the journey to the final product. In the end, we think we nailed it: we now have a wonderfully satisfying, animated, and enthusiastic Duo to cheer you on as you pass significant streak milestones!

An animated gif of Duo becoming the phoenix on fire

The first pass versus the (close to) final product.

And, finally: make the streak shareable

Last but not least, we wanted learners to be able to share their excitement with everyone! Our talented product designers and engineers came up with a wonderfully simple and attractive share card that allows you to easily save, post, or #humblebrag your achievements with friends, family, and social media without having to leave the Duolingo app.

Square images that show the Duolingo owl with fire imagery and say "I just reached a streak!"

Look at me, Mom! Aren’t you proud?!

Onward: keep “powering up” the streak

Here at Duolingo we test everything, but we also recognize that there are certain wins that are hard to quantitatively measure. This streak milestone update has proven to be a success on both fronts. Early metrics have indicated that on both iOS and Android devices, more people are keeping their streaks alive, celebrating their milestones, and continue to march towards their language learning goals! We have also witnessed an overwhelmingly positive reception on Reddit, Twitter, and other social media outlets.

What’s next for Fire Duo? We plan to keep exploring and testing fun ways to celebrate learners on Duolingo. So keep up your practice—you never know what you’ll see on your 100th, or even 1,000th, day of learning!