LangGraph v3 Event Streaming: Typed Projections Over a Content-Block Protocol
Streaming an LLM to a user is easy. Consuming the stream on the server — token deltas, reasoning deltas, tool-call chunks, per-node state, subgraph events, usage metadata — is the part that turns into a pile of if chunk["type"] == ... branches. I shipped a streaming endpoint last week on LangGraph version="v2", because that is what's installed (1.1.8 locally, 1.2.4 on the server). The hand-rolled consumer was about twenty lines of fragile branching, a keepalive hack to stop a proxy from dropping the connection during DeepSeek's silent reasoning phase, and a manual accumulator that reset whenever langgraph_node changed.
LangGraph's version="v3" event-streaming API is what I'd reach for next, and the diff is the interesting part: it deletes most of that parsing. Instead of one undifferentiated event firehose you branch on, v3 gives you typed, per-channel projections you iterate independently, built on a content-block protocol that makes text, reasoning, tool-call, and multimodal boundaries explicit. v1 and v2 are unchanged. This is a walk through what v3 actually is, what it removes from your code, and where it still leaves work for you.