ISSEN Built an AI Tutor You're Supposed to Talk Back To

Open almost any language app and you will be handed a game. Tap the matching tile. Keep the streak alive. Collect the little jewels. It works, up to a point - and then you land in Madrid, someone asks a real question at real speed, and every jewel you collected goes quiet. ISSEN, a company out of Y Combinator's Fall 2024 batch, was built for exactly that gap. Instead of a game, it hands you a voice on the other end of the line and says: talk.

ISSEN is an AI voice tutor. You speak, it listens, it answers, and it keeps a conversation going the way a patient human teacher would - switching between a structured grammar lesson and casual chat, remembering what you covered last time, and nudging you when you stall. It runs on the web, on iOS, and on Android, and it currently handles more than 50 languages, from Spanish and Japanese to Mandarin, Danish, and Cantonese.

01 / THE PROBLEMFluency lives in conversation, not flashcards

The founders' argument is simple, and most language learners feel it in their bones. Conversation is the part that actually makes you fluent, and it is the part almost no app offers. You can drill vocabulary forever and still freeze the moment a live person expects a reply. The traditional fix - a human tutor - works well but costs roughly twenty dollars an hour and has to be scheduled around two people's calendars.

ISSEN's answer is a tutor that is always awake, never annoyed, and costs a fraction of the human rate. You can practice Japanese slang at 6am or run through the past subjunctive at midnight, and there is no one on the other end sighing at your fourth attempt. For a lot of learners, the judgment-free part matters as much as the availability.

02 / THE HARD PARTBefore it could teach, it had to listen

Here is the detail that says the most about how ISSEN was built. The team's hardest engineering problem was not generating clever lessons. It was hearing you. A beginner mangling a tonal vowel on a noisy subway is a nightmare for speech recognition, and if the app cannot understand the learner, nothing else matters. So ISSEN runs your voice through several speech-to-text models at once and reconciles the results, rather than trusting any single one.

How ISSEN hears a learner

You speakAccented, noisy audio

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Stacked STTGemini Flash · Whisper · Scribe · GPT-4o

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Tutor repliesTTS via OpenAI · ElevenLabs · Minimax

03 / THE PRODUCTA tutor with a patience slider

Once ISSEN can understand you, the personality controls are where it gets interesting. You can set the tutor's speaking speed, its patience, how it takes turns, whether it speaks formally or in slang, its accent, and how complex its language gets. You can pick from different AI tutor voices. The flashcards are the part that feels genuinely new: instead of a pre-made word list, ISSEN builds spaced-repetition cards out of the sentences you actually said, so you review your own mistakes rather than a stranger's curriculum.

That single patience slider is worth sitting with. It quietly admits something most apps won't: that learning out loud is uncomfortable, that different people need the machine to wait different amounts, and that the fix is to let the learner set the pace instead of the product setting it for them.

04 / THE DIFFERENCETalking, where the giants make you tap

Duolingo, Babbel, and Memrise dominate the category, and they largely run on gamified exercises - matching, typing, tapping. ISSEN points at the thing those apps deprioritize: sustained, unscripted speech. Its closest peer is Speak, a much better-funded voice-AI company, and general assistants like ChatGPT and Gemini voice modes hover nearby. What ISSEN adds on top is memory, deep customization, and tutors that aren't anchored to English as the native language - useful if you want to learn Portuguese while thinking in Italian.

Where the practice time goes (illustrative)

ISSEN

talk

Human tutor

talk

Gamified app

talk

The founders are also unusually honest about the edges. ISSEN works best for intermediate-to-advanced learners; they have said the beginner experience is still improving. In a category prone to promising fluency to everyone, that restraint reads as a feature.

05 / THE PEOPLETwo Stanford engineers, an odd resume

ISSEN was co-founded by Mariano Sorgente, the CEO, and Anton Apostolatos, who met at Stanford. Sorgente's path here is not the obvious one: he worked on the early Chia blockchain, including foundational pieces like Proof of Space and BLS signatures, and spent time at a16z before turning to language learning - he taught himself Japanese along the way. Apostolatos spent seven years at Palantir, where he worked on infrastructure and helped start the company's Latin America operation, and he grew up trilingual.

06 / THE BUSINESSFree to start, then a subscription

ISSEN is a straightforward consumer subscription. The app is free to download with a short free trial - a few minutes of conversation - after which a paid plan kicks in. Reported pricing runs from roughly twenty to forty dollars a month, with cheaper six- and twelve-month options that vary by platform and region. Its traction signals are real if modest for its age: an App Store rating around 4.7 stars from some 2,800 reviews, and more than half a million downloads on Google Play. The company went through YC's Fall 2024 batch and remains a small, technical team of around three.

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