Flow-IOflow-io
Open Source Voice AIMIT License

The open-source
voice agent platform

Build prompt-based voice AI agents on top of sipgate Flow. Define agent behavior with a system prompt, route calls visually with scenarios, go live in minutes. Self-hostable.

View on GitHubOr try the hosted version
01

Open Source

MIT licensed. Full source code, host it yourself. No black box, no vendor lock-in, no opaque pricing.

02

Prompt-Based Agents

Agent behavior is a system prompt — free-form, not a rigid decision tree. Optionally route between multiple agents with a visual scenario builder.

03

sipgate-Powered

Built on sipgate Flow for European telephony. GDPR-compliant, German data centers, crystal-clear audio.

How It Works

Live in minutes,
not months

01

Connect your sipgate number

Link your sipgate account and route a phone number to your agent. Existing numbers work too.

→ sipgate Flow webhook · OAuth 2.0

02

Write your system prompt

Define your agent's persona, knowledge, and behavior in plain text. Optionally attach a knowledge base for RAG-powered answers.

→ OpenAI · Gemini · bring your own model

03

Deploy & iterate

Go live instantly. Monitor real-time transcripts, review call recordings, and tune your prompt from the dashboard.

→ Multi-tenant · MCP tool integrations

Capabilities

Everything you need,
nothing you don't

Flow-IO ships with the features voice agent builders actually need — without forcing you into a specific platform or workflow.

Multi-LLM Support

Switch between OpenAI GPT-4, Google Gemini, or plug in your own provider. Never locked into a single model or pricing tier.

Knowledge Base & RAG

Upload documents and let your agent answer from them. Chunking, embeddings, and pgvector similarity search built in.

MCP Tool Integrations

Extend your agent with MCP servers. CRM lookups, calendar bookings, custom API calls — your agent handles it all mid-call.

Real-Time Transcripts & Analytics

Full call transcripts, session recordings, and analytics. Understand exactly what your agent says and why.

Why Flow-IO

Open source,
you own it

sipgate Agents are polished and curated — great for standard use cases. Flow-IO is for builders who need full control: custom prompts, any LLM, any integration.

vs sipgate Agents

Full prompt control

✕sipgate Agents: curated steps, constrained behavior
✓Flow-IO: free-form system prompts — your agent does exactly what you tell it
vs Vapi / Bland / Retell

European infrastructure

✕US-only carriers, data leaves Europe, opaque pricing
✓sipgate backbone, GDPR-compliant, German data centers
vs SaaS-only tools

Self-hostable

✕Vendor-hosted only, code stays closed
✓MIT licensed — clone, fork, deploy on your own infra

Open source.
Your infrastructure.

Clone the repo, deploy to your own infrastructure, and own your voice AI stack completely. Or use the hosted version to get started in seconds.

Star on GitHubOr try the hosted version

git clone · docker compose up · done