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Subagent API surface parameterised by the subagent interface type.
Framework adapters supply a class-message variant of
SubagentStreamInterface (where messages is BaseMessage[]
from @langchain/core) so that consumers always work with class
instances. The default parameter keeps the SDK's plain Message
interface for direct SDK usage.
interface SubagentApiCurrently active subagents (where status === "running").
Use this to track and display subagents that are actively executing. Completed or errored subagents are not included.
// Show loading indicators for active subagents
stream.activeSubagents.map(subagent => (
<SubagentCard
key={subagent.id}
type={subagent.toolCall.args.subagent_type}
isLoading={true}
/>
));Get subagent stream by tool call ID.
Use this when you have a specific tool call ID and need to access its corresponding subagent stream.
// In a tool call component
const subagent = stream.getSubagent(toolCall.id);
if (subagent) {
return <SubagentProgress subagent={subagent} />;
}Get all subagents triggered by a specific AI message.
Useful for rendering subagent activities grouped by conversation turn. Each AI message that contains subagent tool calls will have its triggered subagents returned by this method.
// Render subagents inline after the AI message that triggered them
{stream.messages.map((msg) => (
<div key={msg.id}>
<MessageBubble message={msg} />
{msg.type === "ai" && "tool_calls" in msg && (
<SubagentPipeline
subagents={stream.getSubagentsByMessage(msg.id)}
/>
)}
</div>
))}Get all subagents of a specific type.
Returns streams with properly inferred state types based on subagent name. When called with a literal string that matches a subagent name, TypeScript will infer the correct state type for that subagent.
// Get all researcher subagents with typed state
const researchers = stream.getSubagentsByType("researcher");
researchers.forEach(researcher => {
// researcher.values is typed based on ResearchMiddleware
console.log("Research messages:", researcher.values.messages.length);
console.log("Status:", researcher.status);
});
// Get all writer subagents
const writers = stream.getSubagentsByType("writer");
// writers have different state type based on WriterMiddlewareAll currently active and completed subagent streams.
Keyed by tool call ID for easy lookup. Includes subagents in all states: pending, running, complete, and error.
// Iterate over all subagents
stream.subagents.forEach((subagent, toolCallId) => {
console.log(`Subagent ${toolCallId}: ${subagent.status}`);
});
// Get a specific subagent
const specific = stream.subagents.get("call_abc123");