diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2408c7f6..08d65490 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,10 @@
 # Changelog
 ## [Unreleased]
 
+### Fixed
+
+- **AG-UI Activity Events**: Activity events now correctly use structured dict content instead of strings
+
 ## [0.17.2] - 2025-11-19
 
 ### Added
diff --git a/haiku_rag_slim/haiku/rag/graph/agui/emitter.py b/haiku_rag_slim/haiku/rag/graph/agui/emitter.py
index 09201559..b2cf5e3e 100644
--- a/haiku_rag_slim/haiku/rag/graph/agui/emitter.py
+++ b/haiku_rag_slim/haiku/rag/graph/agui/emitter.py
@@ -3,6 +3,7 @@
 import asyncio
 import hashlib
 from collections.abc import AsyncIterator
+from typing import Any
 from uuid import uuid4
 
 from pydantic import BaseModel
@@ -124,13 +125,16 @@ class AGUIEmitter[StateT: BaseModel, ResultT]:
         self._last_state = new_state.model_copy(deep=True)
 
     def update_activity(
-        self, activity_type: str, content: str, message_id: str | None = None
+        self,
+        activity_type: str,
+        content: dict[str, Any],
+        message_id: str | None = None,
     ) -> None:
         """Emit ActivitySnapshot event.
 
         Args:
             activity_type: Type of activity (e.g., "planning", "searching")
-            content: Description of the activity
+            content: Structured payload representing the activity state
             message_id: Optional message ID to associate activity with (auto-generated if None)
         """
         if message_id is None:
diff --git a/haiku_rag_slim/haiku/rag/graph/agui/events.py b/haiku_rag_slim/haiku/rag/graph/agui/events.py
index a7be3d73..eec980f2 100644
--- a/haiku_rag_slim/haiku/rag/graph/agui/events.py
+++ b/haiku_rag_slim/haiku/rag/graph/agui/events.py
@@ -211,14 +211,14 @@ def emit_state_delta(old_state: BaseModel, new_state: BaseModel) -> dict[str, An
 def emit_activity(
     message_id: str,
     activity_type: str,
-    content: str,
+    content: dict[str, Any],
 ) -> dict[str, Any]:
     """Create an ActivitySnapshot event.
 
     Args:
         message_id: Message ID to associate activity with (required)
         activity_type: Type of activity (e.g., "planning", "searching")
-        content: Description of the activity
+        content: Structured payload representing the activity state
 
     Returns:
         ActivitySnapshot event dict
diff --git a/haiku_rag_slim/haiku/rag/graph/common/nodes.py b/haiku_rag_slim/haiku/rag/graph/common/nodes.py
index 31b04b27..bc2da554 100644
--- a/haiku_rag_slim/haiku/rag/graph/common/nodes.py
+++ b/haiku_rag_slim/haiku/rag/graph/common/nodes.py
@@ -75,7 +75,7 @@ def create_plan_node[AgentDepsT: GraphAgentDeps](
 
         if deps.agui_emitter:
             deps.agui_emitter.start_step("plan")
-            deps.agui_emitter.update_activity("planning", activity_message)
+            deps.agui_emitter.update_activity("planning", {"message": activity_message})
 
         try:
             # Build agent configuration
@@ -120,7 +120,7 @@ def create_plan_node[AgentDepsT: GraphAgentDeps](
                 deps.agui_emitter.update_state(state)
                 count = len(state.context.sub_questions)
                 deps.agui_emitter.update_activity(
-                    "planning", f"Created plan with {count} sub-questions"
+                    "planning", {"message": f"Created plan with {count} sub-questions"}
                 )
         finally:
             if deps.agui_emitter:
@@ -198,7 +198,9 @@ async def _do_search[AgentDepsT: GraphAgentDeps](
 ) -> SearchAnswer:
     """Internal search implementation."""
     if deps.agui_emitter:
-        deps.agui_emitter.update_activity("searching", f"Searching: {sub_q}")
+        deps.agui_emitter.update_activity(
+            "searching", {"message": f"Searching: {sub_q}"}
+        )
 
     agent = Agent(
         model=get_model(provider, model),
@@ -248,13 +250,15 @@ async def _do_search[AgentDepsT: GraphAgentDeps](
                     )
                 else:
                     message = success_message_format.format(sub_q=sub_q)
-                deps.agui_emitter.update_activity("searching", message)
+                deps.agui_emitter.update_activity("searching", {"message": message})
         return answer
     except Exception as e:
         if handle_exceptions:
             # Narrate the error
             if deps.agui_emitter:
-                deps.agui_emitter.update_activity("searching", f"Search failed: {e}")
+                deps.agui_emitter.update_activity(
+                    "searching", {"message": f"Search failed: {e}"}
+                )
             failure_answer = SearchAnswer(
                 query=sub_q,
                 answer=f"Search failed after retries: {str(e)}",
diff --git a/haiku_rag_slim/haiku/rag/graph/deep_qa/graph.py b/haiku_rag_slim/haiku/rag/graph/deep_qa/graph.py
index 550dc654..07b6d649 100644
--- a/haiku_rag_slim/haiku/rag/graph/deep_qa/graph.py
+++ b/haiku_rag_slim/haiku/rag/graph/deep_qa/graph.py
@@ -85,7 +85,7 @@ def build_deep_qa_graph(
         if deps.agui_emitter:
             deps.agui_emitter.start_step("decide")
             deps.agui_emitter.update_activity(
-                "evaluating", "Evaluating information sufficiency"
+                "evaluating", {"message": "Evaluating information sufficiency"}
             )
 
         try:
@@ -133,7 +133,9 @@ def build_deep_qa_graph(
                 status = "sufficient" if evaluation.is_sufficient else "insufficient"
                 deps.agui_emitter.update_activity(
                     "evaluating",
-                    f"Information {status} after {state.iterations} iteration(s)",
+                    {
+                        "message": f"Information {status} after {state.iterations} iteration(s)"
+                    },
                 )
 
             should_continue = (
@@ -155,7 +157,7 @@ def build_deep_qa_graph(
         if deps.agui_emitter:
             deps.agui_emitter.start_step("synthesize")
             deps.agui_emitter.update_activity(
-                "synthesizing", "Synthesizing final answer"
+                "synthesizing", {"message": "Synthesizing final answer"}
             )
 
         try:
@@ -195,7 +197,9 @@ def build_deep_qa_graph(
             result = await agent.run(prompt, deps=agent_deps)
 
             if deps.agui_emitter:
-                deps.agui_emitter.update_activity("synthesizing", "Answer complete")
+                deps.agui_emitter.update_activity(
+                    "synthesizing", {"message": "Answer complete"}
+                )
 
             return result.output
         finally:
diff --git a/haiku_rag_slim/haiku/rag/graph/research/graph.py b/haiku_rag_slim/haiku/rag/graph/research/graph.py
index 843bab6b..048c258f 100644
--- a/haiku_rag_slim/haiku/rag/graph/research/graph.py
+++ b/haiku_rag_slim/haiku/rag/graph/research/graph.py
@@ -92,7 +92,7 @@ def build_research_graph(
         if deps.agui_emitter:
             deps.agui_emitter.start_step("analyze_insights")
             deps.agui_emitter.update_activity(
-                "analyzing", "Synthesizing insights and gaps"
+                "analyzing", {"message": "Synthesizing insights and gaps"}
             )
 
         try:
@@ -135,7 +135,9 @@ def build_research_graph(
                 if resolved:
                     parts.append(f"{resolved} resolved")
                 summary = ", ".join(parts) if parts else "No updates"
-                deps.agui_emitter.update_activity("analyzing", f"Analysis: {summary}")
+                deps.agui_emitter.update_activity(
+                    "analyzing", {"message": f"Analysis: {summary}"}
+                )
         finally:
             if deps.agui_emitter:
                 deps.agui_emitter.finish_step()
@@ -148,7 +150,7 @@ def build_research_graph(
         if deps.agui_emitter:
             deps.agui_emitter.start_step("decide")
             deps.agui_emitter.update_activity(
-                "evaluating", "Evaluating research sufficiency"
+                "evaluating", {"message": "Evaluating research sufficiency"}
             )
 
         try:
@@ -199,7 +201,9 @@ def build_research_graph(
                 sufficient = "Yes" if output.is_sufficient else "No"
                 deps.agui_emitter.update_activity(
                     "evaluating",
-                    f"Confidence: {output.confidence_score:.0%}, Sufficient: {sufficient}",
+                    {
+                        "message": f"Confidence: {output.confidence_score:.0%}, Sufficient: {sufficient}"
+                    },
                 )
 
             should_continue = (
@@ -222,7 +226,7 @@ def build_research_graph(
         if deps.agui_emitter:
             deps.agui_emitter.start_step("synthesize")
             deps.agui_emitter.update_activity(
-                "synthesizing", "Generating final research report"
+                "synthesizing", {"message": "Generating final research report"}
             )
 
         try:
diff --git a/tests/graph/agui/test_cli_renderer.py b/tests/graph/agui/test_cli_renderer.py
index b6552bda..8c31f3d3 100644
--- a/tests/graph/agui/test_cli_renderer.py
+++ b/tests/graph/agui/test_cli_renderer.py
@@ -41,7 +41,7 @@ async def test_renderer_basic_flow():
         emit_state_snapshot(SimpleState(value=1)),
         emit_step_started("plan"),
         emit_step_finished("plan"),
-        emit_activity("m1", "planning", "Planning research"),
+        emit_activity("m1", "planning", {"message": "Planning research"}),
         emit_run_finished("t1", "r1", {"status": "complete"}),
     ]
 
@@ -76,7 +76,7 @@ async def test_renderer_handles_all_event_types():
         emit_step_started("step1"),
         emit_step_finished("step1"),
         emit_text_message("message"),
-        emit_activity("m1", "work", "Working"),
+        emit_activity("m1", "work", {"message": "Working"}),
         emit_run_error("error occurred"),
         emit_run_finished("t1", "r1", {"result": "done"}),
     ]
diff --git a/tests/graph/agui/test_emitter.py b/tests/graph/agui/test_emitter.py
index 51c89488..e39f50f1 100644
--- a/tests/graph/agui/test_emitter.py
+++ b/tests/graph/agui/test_emitter.py
@@ -124,8 +124,8 @@ async def test_emitter_activity_events():
     """Test activity events."""
     emitter: AGUIEmitter[TestState, TestResult] = AGUIEmitter()
 
-    emitter.update_activity("processing", "Processing data")
-    emitter.update_activity("done", "Completed", message_id="msg-1")
+    emitter.update_activity("processing", {"message": "Processing data"})
+    emitter.update_activity("done", {"message": "Completed"}, message_id="msg-1")
     await emitter.close()
 
     events = []
@@ -135,7 +135,7 @@ async def test_emitter_activity_events():
     activity_events = [e for e in events if e["type"] == "ACTIVITY_SNAPSHOT"]
     assert len(activity_events) == 2
     assert activity_events[0]["activityType"] == "processing"
-    assert activity_events[0]["content"] == "Processing data"
+    assert activity_events[0]["content"] == {"message": "Processing data"}
     assert activity_events[1]["messageId"] == "msg-1"
     assert activity_events[1]["activityType"] == "done"
 
diff --git a/tests/graph/agui/test_events.py b/tests/graph/agui/test_events.py
index e400f99d..6b807e32 100644
--- a/tests/graph/agui/test_events.py
+++ b/tests/graph/agui/test_events.py
@@ -127,12 +127,12 @@ def test_emit_state_snapshot():
 
 def test_emit_activity():
     """Test ACTIVITY_SNAPSHOT event creation."""
-    event = emit_activity("msg-1", "processing", "Working on task")
+    event = emit_activity("msg-1", "processing", {"message": "Working on task"})
 
     assert event["type"] == "ACTIVITY_SNAPSHOT"
     assert event["messageId"] == "msg-1"
     assert event["activityType"] == "processing"
-    assert event["content"] == "Working on task"
+    assert event["content"] == {"message": "Working on task"}
 
 
 def test_event_structure_consistency():
@@ -145,7 +145,7 @@ def test_event_structure_consistency():
         emit_step_finished("step1"),
         emit_text_message("text"),
         emit_state_snapshot(TestState(value=1)),
-        emit_activity("m1", "type", "content"),
+        emit_activity("m1", "type", {"content": "value"}),
     ]
 
     for event in events:
diff --git a/tests/graph/agui/test_server.py b/tests/graph/agui/test_server.py
index a145f7f6..8a6c78be 100644
--- a/tests/graph/agui/test_server.py
+++ b/tests/graph/agui/test_server.py
@@ -93,7 +93,7 @@ def test_create_agui_app_basic():
     app = create_agui_app(
         graph_factory=graph_factory,  # type: ignore[arg-type]
         state_factory=state_factory,
-        deps_factory=deps_factory,
+        deps_factory=deps_factory,  # type: ignore[arg-type]
         config=config,
     )
 
@@ -124,7 +124,7 @@ def test_server_health_endpoint():
     app = create_agui_app(
         graph_factory=graph_factory,  # type: ignore[arg-type]
         state_factory=state_factory,
-        deps_factory=deps_factory,
+        deps_factory=deps_factory,  # type: ignore[arg-type]
         config=config,
     )
 
@@ -159,7 +159,7 @@ async def test_server_stream_endpoint():
     app = create_agui_app(
         graph_factory=graph_factory,  # type: ignore[arg-type]
         state_factory=state_factory,
-        deps_factory=deps_factory,
+        deps_factory=deps_factory,  # type: ignore[arg-type]
         config=config,
     )
 
@@ -222,7 +222,7 @@ def test_server_cors_headers():
     app = create_agui_app(
         graph_factory=graph_factory,  # type: ignore[arg-type]
         state_factory=state_factory,
-        deps_factory=deps_factory,
+        deps_factory=deps_factory,  # type: ignore[arg-type]
         config=config,
     )
 
diff --git a/tests/graph/agui/test_stream.py b/tests/graph/agui/test_stream.py
index daa428b0..04d9a0b3 100644
--- a/tests/graph/agui/test_stream.py
+++ b/tests/graph/agui/test_stream.py
@@ -36,7 +36,7 @@ class MockGraph:
         # Emit some events through the emitter
         if deps.agui_emitter:
             deps.agui_emitter.start_step("mock_step")
-            deps.agui_emitter.update_activity("working", "Doing work")
+            deps.agui_emitter.update_activity("working", {"message": "Doing work"})
             deps.agui_emitter.finish_step()
 
         return self.result
@@ -50,7 +50,7 @@ async def test_stream_graph_basic():
     deps = TestDeps()
 
     events = []
-    async for event in stream_graph(graph, state, deps):
+    async for event in stream_graph(graph, state, deps):  # type: ignore[arg-type]
         events.append(event)
 
     # Should have collected events
@@ -73,7 +73,7 @@ async def test_stream_graph_emits_initial_state():
     deps = TestDeps()
 
     events = []
-    async for event in stream_graph(graph, state, deps):
+    async for event in stream_graph(graph, state, deps):  # type: ignore[arg-type]
         events.append(event)
 
     # Should have initial state snapshot
@@ -91,7 +91,7 @@ async def test_stream_graph_emits_step_events():
     deps = TestDeps()
 
     events = []
-    async for event in stream_graph(graph, state, deps):
+    async for event in stream_graph(graph, state, deps):  # type: ignore[arg-type]
         events.append(event)
 
     # Should have step events from MockGraph
@@ -108,13 +108,13 @@ async def test_stream_graph_emits_activity():
     deps = TestDeps()
 
     events = []
-    async for event in stream_graph(graph, state, deps):
+    async for event in stream_graph(graph, state, deps):  # type: ignore[arg-type]
         events.append(event)
 
     # Should have activity events from MockGraph
     activities = [e for e in events if e["type"] == "ACTIVITY_SNAPSHOT"]
     assert len(activities) > 0
-    assert activities[0]["content"] == "Doing work"
+    assert activities[0]["content"] == {"message": "Doing work"}
 
 
 @pytest.mark.asyncio
@@ -130,7 +130,7 @@ async def test_stream_graph_handles_error():
     deps = TestDeps()
 
     events = []
-    async for event in stream_graph(graph, state, deps):
+    async for event in stream_graph(graph, state, deps):  # type: ignore[arg-type]
         events.append(event)
 
     # Should have error event
@@ -154,7 +154,7 @@ async def test_stream_graph_closes_emitter():
 
     events = []
     try:
-        async for event in stream_graph(graph, state, deps):
+        async for event in stream_graph(graph, state, deps):  # type: ignore[arg-type]
             events.append(event)
     except RuntimeError:
         # Expected - graph didn't return a result
@@ -190,7 +190,7 @@ async def test_stream_graph_result_in_finish_event():
     deps = TestDeps()
 
     events = []
-    async for event in stream_graph(graph, state, deps):
+    async for event in stream_graph(graph, state, deps):  # type: ignore[arg-type]
         events.append(event)
 
     # Find RUN_FINISHED event