Migrate from Anthropic Managed Agents

If you already have working code against Anthropic Managed Agents and you want to switch your session storage to Durable Sessions, the migration is almost free. The event format, the endpoint paths, and the request/response shapes are intentionally compatible. You change two headers and one base URL.

What changes

	Anthropic Managed Agents	Durable Sessions
Base URL	https://api.anthropic.com	https://sessions.tonbo.dev
Auth header	x-api-key: $ANTHROPIC_API_KEY	Authorization: Bearer $TONBO_API_KEY (or x-api-key — both accepted)
Beta header	anthropic-beta: managed-agents-2026-04-01	(not needed, drop it)
Version header	anthropic-version: 2023-06-01	(not needed, drop it)
Send events body	{ "events": [{...}] }	Same — also accepts [{...}] and {...}
Read events response	{ "data": [...] }	Same
SSE stream path	GET /v1/sessions/{id}/stream	Same — and you can also use GET /v1/sessions/{id}/events?live=sse&offset=now for explicit offset control

What stays the same

Your event handling code is unchanged. Every event type Anthropic uses is also a valid Durable Sessions event type:

• user.message, user.interrupt, user.tool_confirmation, user.custom_tool_result
• agent.message, agent.thinking, agent.tool_use, agent.tool_result
• session.status_running, session.status_idle, session.status_terminated
• span.model_request_start, span.model_request_end

Content blocks ({type: "text", text}, {type: "image", source}, etc.) work identically.

What you give up

Durable Sessions is just the session layer. We don't manage agents, environments, or sandboxes. So these endpoints from Anthropic don't have a Durable Sessions equivalent:

• POST /v1/agents — agent definitions live in your own code
• POST /v1/environments — your sandbox is whatever you choose (Docker, Firecracker, E2B, your own)
• The harness loop — bring your own (or use Claude Code, Codex, OpenCode, etc.)

If you were using Anthropic for the whole stack including harness execution and sandbox compute, migrating to Durable Sessions means you also need to bring your own harness and sandbox. If you already have those (most platform teams do), you're free of the bundled charges.

What you gain

These are Durable Sessions features Anthropic Managed Agents doesn't have:

• Full-text search — GET /v1/sessions/{id}/events?q=stripe+webhook returns BM25-ranked relevant events. Stop stuffing the prompt with the last N events.
• Explicit offset-based streaming — ?offset=now or ?offset=00000145 eliminates the SSE race condition where you must open the stream before sending events.
• Type filtering — ?type=agent.tool_use returns only matching events.
• Your own S3 bucket — every event lives in storage you own. Export, audit, walk away anytime.
• Open protocol — built on Durable Streams, self-hostable and forkable.
• Lower price for the session layer alone — about 1/130th of Anthropic's bundled session-hour fee at the same workload (see Overview → Why not Anthropic).

Migration in code

Anthropic Python SDK → Durable Sessions

Set the base URL and API key when constructing the client. Nothing else changes.

from anthropic import Anthropic

# Before
client = Anthropic()
# After
client = Anthropic(
    base_url="https://sessions.tonbo.dev",
    api_key="your-tonbo-api-key",
)

# Existing send/read/stream code works as-is
client.beta.sessions.events.send(
    session_id,
    events=[
        {
            "type": "user.message",
            "content": [{"type": "text", "text": "..."}],
        },
    ],
)

Raw curl

# Before — Anthropic
curl https://api.anthropic.com/v1/sessions/$SESSION_ID/events \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "anthropic-beta: managed-agents-2026-04-01" \
  -H "content-type: application/json" \
  -d '{"events":[{"type":"user.message","content":[{"type":"text","text":"..."}]}]}'

# After — Durable Sessions
curl https://sessions.tonbo.dev/v1/sessions/$SESSION_ID/events \
  -H "Authorization: Bearer $TONBO_API_KEY" \
  -H "content-type: application/json" \
  -d '{"events":[{"type":"user.message","content":[{"type":"text","text":"..."}]}]}'

The body is identical. The two anthropic-* headers are gone. The auth header changed from x-api-key to Authorization: Bearer.

Migrating session metadata

Anthropic's POST /v1/sessions request body looks like this:

{
  "agent": "agt_abc123",
  "environment_id": "env_xyz",
  "title": "My session"
}

Durable Sessions accepts the same body unchanged. The agent and environment_id fields are stored as opaque session metadata — they don't trigger any harness or sandbox provisioning, but they're preserved for your own reference and queryable via GET /v1/sessions/{id}.

You can also send a generalized form with custom metadata:

{
  "title": "My session",
  "metadata": {
    "agent": "agt_abc123",
    "environment_id": "env_xyz",
    "user_email": "[email protected]",
    "experiment": "v2"
  }
}

After the migration

• Your Anthropic API key is no longer used for session storage. Keep it if you're still calling the Messages API directly.
• Run your existing harness against Durable Sessions and watch the events flow into your S3 bucket.
• Compare cost: a workload that ran $2,400/month on Anthropic Managed Agents typically runs ~$18.50/month on Durable Sessions (you keep your own harness and sandbox compute, of course).

Need help migrating a real workload? Book a call and we'll walk through it together.