Tier 2 — Modal

Runs the same hosting/Dockerfile image on Modal via modal.Sandbox. You get a public HTTPS URL, scale-to-zero, and no infrastructure to manage.

Prerequisites

pip install modal
modal setup            # opens a browser to authenticate
modal secret create anthropic ANTHROPIC_API_KEY="$ANTHROPIC_API_KEY"

Deploy

cd claude_agent_sdk/
python hosting/modal/modal_app.py

This builds the Dockerfile remotely on Modal (build context = claude_agent_sdk/, same as local), starts a sandbox running serve, and prints a tunnel URL.

Talk to it

The deploy script prints a url: and a token: line. The tunnel URL is public, so the server requires the bearer token on the messages endpoint (only /health is open):

curl -N -X POST "$MODAL_URL/sessions/demo-1/messages" \
  -H "Authorization: Bearer $MODAL_TOKEN" \
  -H 'Content-Type: application/json' \
  -d '{"prompt":"What are the latest AI agent trends?"}'

Persistence

By default modal_app.py mounts a modal.Volume at /data — the same CLAUDE_CONFIG_DIR trick as tier 1. Session transcripts survive sandbox restarts.

Note: modal.Volume has explicit commit semantics. If your workload has many sandboxes writing many sessions concurrently and you see lost writes, switch to a SessionStore backed by Modal Dict or an external store — that's also what tier 3 uses.

Liveness

Modal keeps the sandbox running until the timeout= passed to Sandbox.create expires; it does not probe GET /health. If the server inside dies, the sandbox stays up and requests fail until the timeout reaps it. For anything longer-lived than a demo, point your own monitoring at /health and recreate the sandbox when it stops answering.

Teardown

python hosting/modal/teardown.py

Stops sandboxes and removes the volume so you're not billed for idle resources.