Who's building this
Northline is made by Synthemo, which is one person: Philip Benn, a creative technologist with fifteen years in computer graphics. The rest of the team is AI. Claude writes and reviews code with him, runs the tests, and helps work through the hard calls, like what a digital twin should never tell a stranger.
Listening
Deepgram Flux
Speech recognition built for conversation. Flux listens for the end of a turn, not just the end of a word, so a persona can tell a pause from being done and answer without the awkward wait.
Thinking
Claude Sonnet 5
The brain of every persona. Each one runs on Claude, shaped by its own character file and one shared set of rules none of them can break. It remembers you across conversations, just you, and it can search the web when a question needs it.
Responding
ElevenLabs v3 Conversational + LemonSlice
Each persona has a voice of its own, streamed sentence by sentence as it thinks, so replies start fast. In avatar mode, LemonSlice renders a live face in real time, delivered over LiveKit.
Under the hood: Next.js on Vercel, a Python API and workers on Render, Postgres on Neon, and LiveKit for real-time media.