feat(multiagent): introduce Swarm multi-agent orchestrator

Author: awsarron

src/strands/agent/agent.py

@@ -317,6 +317,9 @@ def __init__(
                 self.hooks.add_hook(hook)
         self.hooks.invoke_callbacks(AgentInitializedEvent(agent=self))
 
+        # When True, force stops the agent's event loop
+        self.stop_event_loop = False
+
     @property
     def tool(self) -> ToolCaller:
         """Call tool as a function.

src/strands/event_loop/event_loop.py

@@ -462,7 +462,7 @@ def tool_handler(tool_use: ToolUse) -> ToolGenerator:
         tracer = get_tracer()
         tracer.end_event_loop_cycle_span(span=cycle_span, message=message, tool_result_message=tool_result_message)
 
-    if invocation_state["request_state"].get("stop_event_loop", False):
+    if agent.stop_event_loop or invocation_state["request_state"].get("stop_event_loop", False):
         agent.event_loop_metrics.end_cycle(cycle_start_time, cycle_trace)
         yield {"stop": (stop_reason, message, agent.event_loop_metrics, invocation_state["request_state"])}
         return

src/strands/multiagent/__init__.py

@@ -11,11 +11,15 @@
 from . import a2a
 from .base import MultiAgentBase, MultiAgentResult
 from .graph import GraphBuilder, GraphResult
+from .swarm import Swarm, SwarmConfig, SwarmResult
 
 __all__ = [
     "a2a",
     "GraphBuilder",
     "GraphResult",
     "MultiAgentBase",
     "MultiAgentResult",
+    "Swarm",
+    "SwarmConfig",
+    "SwarmResult",
 ]

src/strands/multiagent/base.py

@@ -58,9 +58,15 @@ def get_agent_results(self) -> list[AgentResult]:
 
 @dataclass
 class MultiAgentResult:
-    """Result from multi-agent execution with accumulated metrics."""
+    """Result from multi-agent execution with accumulated metrics.
 
-    results: dict[str, NodeResult]
+    The status field represents the outcome of the MultiAgentBase execution:
+    - COMPLETED: The execution was successfully accomplished
+    - FAILED: The execution failed or produced an error
+    """
+
+    status: Status = Status.PENDING
+    results: dict[str, NodeResult] = field(default_factory=lambda: {})
     accumulated_usage: Usage = field(default_factory=lambda: Usage(inputTokens=0, outputTokens=0, totalTokens=0))
     accumulated_metrics: Metrics = field(default_factory=lambda: Metrics(latencyMs=0))
     execution_count: int = 0

src/strands/multiagent/graph.py

@@ -66,14 +66,8 @@ class GraphState:
 
 @dataclass
 class GraphResult(MultiAgentResult):
-    """Result from graph execution - extends MultiAgentResult with graph-specific details.
+    """Result from graph execution - extends MultiAgentResult with graph-specific details."""
 
-    The status field represents the outcome of the graph execution:
-    - COMPLETED: The graph execution was successfully accomplished
-    - FAILED: The graph execution failed or produced an error
-    """
-
-    status: Status = Status.PENDING
     total_nodes: int = 0
     completed_nodes: int = 0
     failed_nodes: int = 0
@@ -468,12 +462,12 @@ def _build_node_input(self, node: GraphNode) -> str:
     def _build_result(self) -> GraphResult:
         """Build graph result from current state."""
         return GraphResult(
+            status=self.state.status,
             results=self.state.results,
             accumulated_usage=self.state.accumulated_usage,
             accumulated_metrics=self.state.accumulated_metrics,
             execution_count=self.state.execution_count,
             execution_time=self.state.execution_time,
-            status=self.state.status,
             total_nodes=self.state.total_nodes,
             completed_nodes=len(self.state.completed_nodes),
             failed_nodes=len(self.state.failed_nodes),