Streaming

There are two complementary APIs:

1. Callback-style — pass onAssistantDelta (or OnAssistantDelta in Go) to a regular runAgent / Send call. The promise/result still resolves with the final text.
2. Iterator-style — call streamAgent / Session.Stream to get an async iterator (or channel in Go) of every event.

TypeScript

// Callback
await client.runAgent({
  systemPrompt: "...",
  prompt: "Tell me a story.",
  onAssistantDelta: (delta) => process.stdout.write(delta),
});

// Iterator
for await (const event of client.streamAgent({
  systemPrompt: "...",
  prompt: "Tell me a story.",
})) {
  if (event.type === "assistant_delta") process.stdout.write(event.text);
  if (event.type === "result") process.stdout.write("\n");
}

Python

# Callback
client.run_agent(
    system_prompt="...",
    prompt="Tell me a story.",
    on_assistant_delta=lambda d: print(d, end="", flush=True),
)

# Iterator
for event in client.stream_agent(system_prompt="...", prompt="Tell me a story."):
    if event.type == "assistant_delta":
        print(event.text, end="", flush=True)

# Async iterator
async for event in async_client.stream_agent(system_prompt="...", prompt="..."):
    ...

Go

// Callback
_, _ = client.RunAgent(ctx, mantyx.RunSpec{
    SystemPrompt:     "...",
    Prompt:           "Tell me a story.",
    OnAssistantDelta: func(s string) { fmt.Print(s) },
})

// Channel
ch, err := client.StreamAgent(ctx, mantyx.RunSpec{
    SystemPrompt: "...",
    Prompt:       "Tell me a story.",
})
if err != nil { log.Fatal(err) }
for ev := range ch {
    if ev.Type == "assistant_delta" {
        if t, ok := ev.Data["text"].(string); ok {
            fmt.Print(t)
        }
    }
}

What events to expect

Event	When	Payload
assistant_delta	Streaming assistant tokens	{ text }
thinking_delta	Reasoning models with reasoningLevel > 0 emit chain-of-thought tokens	{ text }
assistant_message	Full assistant turn (text + tool calls)	{ text, toolCalls }
tool_call / tool_result	Server-side tool execution	{ toolUseId, name, ... }
local_tool_call	The SDK should run a handler	{ toolUseId, name, args, kind?, ... }
local_tool_result_in	Echo of the SDK’s result	{ toolUseId, output }
result	Terminal	{ subtype, text?, error? }
cancelled	Terminal (after cancelRun)	{}

The local_tool_call payload carries a kind discriminator ("local" when omitted, "a2a_local", or "mcp_local") plus extra metadata for the specialised kinds. The SDKs route to the right handler automatically; you only need to care about this if you’re implementing a third-party client. The full event vocabulary is documented in Wire protocol §7.

The SDKs all reconnect automatically via Last-Event-ID + ?lastSeq= if the SSE stream drops.