LangGraph Agent Server compatibility

Use this reference before pointing an existing LangChain client at skein-js. Start with your current langgraph.json and SDK, run a known input, and verify the behavior your application uses with project smoke tests.

Verified client combinations

Client or surface	Verified combination and behavior
JavaScript SDK	Legacy SDK 1.9.25/1.9.31 and thread-protocol SDK 1.12.6; examples also use 1.12.7
React	Dedicated @langchain/react 1.2.6 and 1.2.7; legacy SDK React hook remains supported
Angular, Vue, Svelte	Dedicated packages 1.2.6, exercised in Chromium
Thread subscriptions	Multiple turns, restoration, interrupt/resume, cancellation, and reconnect; reconnect does not start another run
Cross-instance reconnect	Express with Redis queues and thread event buses
Memory and retention options	Memory, SQLite, and Postgres store indexing, write TTL, and per-read refresh controls
MCP	Official MCP SDK 1.32.1, stateless Streamable HTTP
A2A	Official A2A SDK 1.3.0, retained task output and interrupt handling
Compiled UI and custom applications	UI compiler 1.4.2; Node 24 production artifact with SQLite
Diagnostics	Checkpoint payload accounting with memory, SQLite, and Postgres; Prometheus and OTLP JSON output

These combinations establish the listed behavior, rather than universal compatibility with every version or backend. The workspace uses LangGraph.js 1.4.7 and a packed consumer uses 1.4.12. Thread-event execution requires LangGraph's public streamEvents({ version: "v3" }) capability; legacy execution remains available for older graphs and custom agents.

For frontend setup, use the SDK guide. For configuration and exact wire contracts, use CLI compatibility and the protocol reference.

Client limitations

• Svelte 1.2.6: root useImages returns an empty projection. Use a scoped media selector for the subgraph namespace containing the media.
• Vue 1.2.6: unwrap a media asset with toRaw(asset) before reading blob; see the frontend workaround.
• Development UI watchers: follow the upstream watcher's process lifetime. Your host owns shutdown.

Intentional differences

• HTTP/SSE is supported; WebSockets and gRPC are outside the compatibility target.
• Stateless runs keep their threads by default. Set on_completion: "delete" to remove them.
• Store ordering filters compare numbers only.
• Local SQLite persists resources and checkpoints; event replay is process-local and is lost on restart.
• Skein adds idempotent run creation and durable, signed, retried webhook delivery. LangGraph also supports ordinary run-completion webhooks.
• Managed hosting, billing, evaluations, and application identity policy remain application or service choices.

Contributor investigation and dated test evidence are recorded in the testing guide.