banter

Pick a scene (ordering dinner, a job interview, haggling at a market), a language (Spanish, French, German, Italian or Japanese) and a difficulty, and hold a real spoken conversation with an animated partner (a photoreal video partner on the Studio plan) who stays in character, can be interrupted mid-sentence, and wraps the scene up as the clock runs down. A live coach flags lines that didn't land while they can still be retried, and every session ends in a 0–100 Banter Score with a CEFR band and corrections quoted in the learner's own words. The first 3-minute conversation is free; Practice and Studio plans are sold through Stripe.

Language apps drill vocabulary, but fluency comes from speaking under the mild pressure of a real exchange — and most learners have nobody to practise with, and no honest measure of whether they're improving.

Every vendor sits behind a provider interface with a mock, so the whole product runs with no keys at all. In production the browser streams audio straight to Amazon Transcribe and, on the Studio plan, video from Anam, using short-lived credentials minted per session behind auth and quota checks; Claude on Bedrock drives the persona, a separate live coach, and the scoring. The Banter Score is a weighted formula over named sub-scores, stored with its version, so a learner's number is reproducible and comparable week to week. Minutes are reserved atomically in Aurora before any credential is minted, and both the speech and avatar vendors cut a session off at the plan's cap themselves.

• Browser-to-vendor media path: streaming speech-to-text and a WebRTC video avatar, with no vendor key ever reaching the browser
• Claude Haiku 4.5 plays the persona and the live coach; Claude Opus 4.5 scores the conversation
• An explicit, versioned scoring formula — the model supplies judgement, never the arithmetic
• Vendor-enforced session caps on both speech and avatar, so a runaway client can't run up the bill
• Atomic minute reservations in Postgres, proven by an integration test that races concurrent sessions

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