LangSmith

Choose the LangSmith target when LangSmith, or another LangGraph deployment platform, must handle transport and execution. This target emits graph entries for the platform to run, without B4.run's HTTP server.

Select the target#Copy link to section: Select the target

B4.run emits LangSmith by default alongside Node. To emit only the platform artifact:

import { config } from "@b4run/cli"
 
export default config({
  build: { targets: ["langsmith"] },
})

Build output#Copy link to section: Build output

Run the usual validation and build flow:

b4 check
b4 build
b4 verify

The target writes .b4/build/langgraph.json and one .b4/build/<route-slug>.ts entry per discovered route. Here is a representative config:

{
  "graphs": {
    "/navlog#agent": "./.b4/build/navlog.ts:graph"
  },
  "dependencies": ["."],
  "env": ".env.example",
  "node_version": "22"
}

Each graph key is <routeId>#<kind>. Use the full key, such as /navlog#agent, as the platform assistant_id.

Route entry behavior#Copy link to section: Route entry behavior

Agent routes receive a generated entry that calls materializeResolvedRouteGraph. That path loads the agent descriptor and applies B4.run's agent materialization, including discovered route tools, tool scope, capabilities and permission gates.

Workflow, graph and chain routes skip agent materialization. Their generated entry imports the route's workflow, graph or chain export and re-exports it as graph.

Test every route kind you deploy on the platform itself. B4.run's HTTP scenario tests never see the platform's assistant_id request envelope.

Environment file path#Copy link to section: Environment file path

The generated env field is .env.example when that file exists at the app root, and .env otherwise. The platform build reads this path. Review the selected file before you deploy, and keep secret values in the platform's secret manager, out of Git.

Merge precedence#Copy link to section: Merge precedence

If the app root contains a hand-authored langgraph.json, B4.run shallow-merges it into the generated output. User-defined extra keys survive. The generated graphs, dependencies, env, and node_version fields overwrite user values with those names.

The merge is shallow, so a user graphs map is replaced as a whole.

Platform authentication and missing B4.run surfaces#Copy link to section: Platform authentication and missing B4.run surfaces

Configure authentication and tenant authorization on LangSmith or your hosting platform. The generated target does not include B4.run HTTP middleware, the AG-UI server, the B4.run sandbox manager or B4.run's Agent Protocol thread-management server.

Agent routes still get policy-aware graph construction. If you need the HTTP or sandbox surfaces, deploy Node and Docker, or Edge and Hono if your app passes its capability gate.

Node version mismatch#Copy link to section: Node version mismatch

The emitter currently writes node_version: "22", but B4.run packages require Node 24 or newer. As of this writing, that mismatch is unresolved. B4.run isn't known to run correctly on Node 22, so confirm the platform's supported Node versions before you deploy.

Deployment checklist#Copy link to section: Deployment checklist

1. Confirm that every route has the expected <routeId>#<kind> entry and use it as assistant_id.
2. Inspect the environment-file path and move actual secrets into platform-managed configuration.
3. Add platform authentication and tenant authorization.
4. Test agent materialization and raw workflow/graph/chain entries through the platform transport.
5. Resolve the Node 22/Node 24 incompatibility with the target platform before production use.
6. Confirm that no requirement depends on B4.run HTTP middleware, AG-UI, or the sandbox manager.

Troubleshooting#Copy link to section: Troubleshooting

• A user config field disappeared: generated graphs, dependencies, env and node_version take precedence by design.
• The platform can't find an assistant: use the full <routeId>#<kind> key from generated graphs.
• HTTP middleware didn't run: these entries don't include it. Enforce authentication on the platform.
• Local Node HTTP tests pass but platform calls fail: exercise the platform transport and its environment/build process directly.