About Patter

Open-source voice AI infrastructure

What Patter is

Patter is an open-source SDK that connects any AI agent to a real phone number. It handles the parts of voice AI that are tedious and easy to get wrong — carrier signalling, bidirectional audio streaming, turn detection, barge-in, call recording, transfers and DTMF — so that giving an agent a phone number takes four lines of code instead of a bespoke telephony integration.

The SDK ships for Python and TypeScript under the same API surface, and is published as getpatter on both PyPI and npm. It is licensed MIT, and it is self-hosted: Patter runs inside your own infrastructure, talking directly to the providers you already pay for. There is no Patter account, no API key, and no per-minute fee on top of your carrier and model bills.

How it works

Patter supports two architectures. In engine mode a single speech-to-speech model such as OpenAI Realtime or ElevenLabs ConvAI handles the whole conversation. In pipeline mode you compose speech-to-text, an LLM and text-to-speech independently, mixing providers freely — Deepgram, Whisper, Cartesia, Soniox, Speechmatics or AssemblyAI for transcription; OpenAI, Anthropic, Groq, Cerebras or Google for reasoning; ElevenLabs, OpenAI, Cartesia, Rime or LMNT for speech. Telephony runs over Twilio or Telnyx.

Every provider is a typed instance with environment-variable fallback, so swapping one out is a one-line change rather than a rewrite. Tool calling, output guardrails, dynamic variables, event hooks, OpenTelemetry tracing and a built-in metrics dashboard are part of the SDK rather than add-ons.

Why we built it

Voice agents were being locked behind closed hosted platforms that charged per minute, restricted which models you could run, and kept your call data on their infrastructure. We think the interesting work happens in the agent, not in the plumbing underneath it — and that the plumbing should be inspectable, forkable and free. Patter is the alternative to Vapi, Bland AI and Retell for teams that want to own their stack.

The company

Patter is built by Patter, Inc. The source code lives on GitHub at github.com/PatterAI/Patter, where issues and pull requests are the fastest way to reach the maintainers. Patter Cloud — a managed platform built on the same SDK, for teams that would rather not run the infrastructure themselves — is in development, and you can join the waiting list.

Get in touch

General enquiries go to hello@getpatter.com. Security reports go to security@getpatter.com. See the contact page for every channel, or book a call to talk to us directly.