Duolingo uses a large language model from OpenAI (GPT-4) to power live conversation practice inside its app. Learners can text-chat with AI characters in simulated real-world scenarios, or video-call an animated AI character named Lily who speaks and responds in real time. These features launched in 2023 and are available to paid subscribers.

Launched March 14, 2023 as part of the Duolingo Max subscription tier ($29.99/month), Roleplay places learners in scenarios like ordering coffee or planning a trip, with the large language model generating dynamic character responses constrained by educational prompts. Video Call — announced September 24, 2024 — adds spoken voice interaction with Lily, an animated AI character who adjusts to the learner's skill level, pauses to simulate thinking, and retains memory of past conversations. The system expanded to Android and nine languages by 2025. Each conversation is unique because the AI generates responses on the fly rather than selecting from pre-written scripts.