Module 6, Lesson 120 min

Stream modes: values, updates, messages, custom

Autonomy is invisible today: Impulse rolls a dice and you find out from a log later. This module streams a graph run node-by-node into a browser panel, the same SSE pattern cockpit already uses. You will watch a dice roll happen live from your phone.

Streaming turns one blocking call into a sequence of events. Instead of await graph.invoke(…) returning once at the end, graph.stream(…) yields chunks as the graph runs.

Streaming state updates

for await (const chunk of await graph.stream(inputs, { streamMode: "updates" })) {
  // chunk is the state delta from the node that just ran
}

Stream modes decide what each chunk contains: values is the full state after each step; updates is only the delta each node returned (best for “which node just ran and what did it write”); messages is LLM tokens as they generate, for typewriter output; custom is arbitrary events you emit yourself from inside a node.

Combining stream modes

for await (const [mode, chunk] of await graph.stream(inputs, {
  streamMode: ["updates", "custom"],
})) {
  if (mode === "custom") renderDiceEvent(chunk);
  else lightUpNode(chunk);
}

Pass an array to combine modes; chunks then arrive as [mode, chunk] tuples so you can tell them apart.

Practice

Try it yourself

Quiz

values vs updates for lighting up nodes

You want to light up the node that just ran in a live panel. Which stream mode do you want?

Avalues, because it always has the full picture of state
Bmessages, because it streams the fastest
Cupdates, because it's only the delta the node just returned, so you see exactly what it wrote
DIt doesn't really matter, both give you identical information anyway

Show answer

Correct answer: C — updates, because it's only the delta the node just returned, so you see exactly what it wrote

updates gives you just the delta from the node that ran -- exactly what you need to know "this node ran, here's what it wrote" without having to diff two full-state snapshots yourself.