Every call is paid: route-level middleware

Deploy a LangGraph agent to LangSmith Deployment and gate its runs/wait endpoint with the Nevermined x402 flow — a single env file plus four lines of glue.

langchain-langsmith-deployment-py/

1 What you'll learn

When there's no free tier: gate the whole route, not a single tool.

Gate POST /threads/{id}/runs/wait with the payments-py ASGI PaymentMiddleware
Keep POST /threads and discovery endpoints free; protect only the run
Return 402 + the x402 envelope, then 200 + the settlement receipt on retry
Deploy the graph to hosted LangSmith Deployment with langgraph up

2 How it works

The middleware follows the canonical x402 lifecycle: verify → agent runs → settle, and only settles if the agent succeeded. Failed runs don't bill the buyer; settlement failures after a successful run are logged but never surface to the client — the buyer already got the value.

Use this pattern when every message is paid. For a free-introspection concierge, use the in-tool gating of the research agent instead.

verifypayment-signature

agent runsthe graph

settleonly if it succeeded

3 Under the hood

LangSmith DeploymentLangGraphpayments-pyDockerPython 3.11–3.13

# the gated endpoint map

POST /threads               → free
POST /threads/{id}/runs/wait → PAID (402 → 200 + receipt)
GET  /assistants/search, /info, /ok → pass through

src/nvm_app.py	four lines of glue that wrap the app with PaymentMiddleware
src/buyer.py	drives the 402 round-trip and prints the settlement receipt

4 See it run

Every call is paid: route-level middleware

Sandbox agent — real payment round-trips (402 → authorize → settle) with a per-session credit balance, no external service and no real money. The runs/wait route is gated by route-level ASGI middleware; the sandbox runs the 402 round-trip locally. See the README to call a hosted LangSmith deployment.