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Pick a backend

Three backends, three different sweet spots.

Backend Pick it when…
Google ADK (default) You want production session storage out of the box (Postgres), FastAPI surface, plugin system, ADK's WebSocket streaming. Most batteries included. Default for nuvel new.
Claude Agent SDK You want Anthropic's first-party agent loop, async streaming via receive_response(), fewer infra primitives, lower-level control over the agent's turn cycle.
Anthropic Managed Agents You don't want to operate session state at all — Anthropic owns the runtime. Smallest infra footprint; least flexibility.

Concrete differences

Session / state

  • ADK has BaseSessionService with in-memory and Postgres implementations. Sessions persist across restarts in production. ADK is the only backend that handles long-running user conversations cleanly.
  • Claude Agent SDK has session IDs but state is a thin wrapper — you persist what you need yourself.
  • Anthropic Managed Agents stores session state server-side. You get session IDs and resumption for free, but you can't introspect or rewind.

Tool-calling shape

  • ADK — Python tools registered on LlmAgent(tools=[...]). ADK normalizes calling conventions. Composio MCP toolset is supported.
  • Claude Agent SDK — tool definitions in JSON Schema, callbacks dispatched per turn.
  • Anthropic Managed Agents — tools defined when you register the managed agent; runtime calls are server-side.

Streaming

  • ADK — WebSocket-based, opt-in via STREAMING_ENABLED=true (overrides model to Gemini for live streaming).
  • Claude Agent SDK — first-class. client.receive_response() is an async iterator over the agent's reply stream.
  • Anthropic Managed Agents — server-side; you receive events through the managed-agent API.

nuvel feature support

Feature ADK Claude SDK Anthropic Managed
--persona ✅ ❌ ❌
--with-composio ✅ ❌ ❌
--with-slack / --with-telegram / --with-teams ✅ ❌ ❌
Bundled skills ✅ ✅ ✅
Generated FastAPI server ✅ ✅ ✅
Production Postgres sessions ✅ manual server-side
Railway-ready Dockerfile ✅ ✅ ✅

The advanced bundles (persona, composio, channels) are ADK-only today because that's where the runtime primitives are richest. The other two backends accept the flags but exit with a "not yet supported" error, so a future you can find them via nuvel new --help.

When to switch

You can scaffold a new agent on a different backend without disturbing existing agents — they don't share runtime. There's no built-in "migrate" path; the prompt and skills are portable, but session data is not.

Default

If you have no strong reason to pick another, stay on ADK. It's the most-tested path through nuvel and the one that gets new features first.