feat(agent): expose system_prompt_content as public property

src/strands/agent/agent.py

@@ -412,6 +412,18 @@ def system_prompt(self, value: str | list[SystemContentBlock] | None) -> None:
         """
         self._system_prompt, self._system_prompt_content = self._initialize_system_prompt(value)
 
+    @property
+    def system_prompt_content(self) -> list[SystemContentBlock] | None:
+        """Get the system prompt as content blocks.
+
+        Returns the full content block representation, preserving cache control
+        and non-text content. Returns None if no system prompt is set.
+
+        Returns:
+            The system prompt as a list of SystemContentBlock objects, or None.
+        """
+        return self._system_prompt_content
+
     @property
     def tool(self) -> _ToolCaller:
         """Call tool as a function.

src/strands/event_loop/event_loop.py

@@ -314,7 +314,7 @@ async def _handle_model_execution(
             model_id=model_id,
             custom_trace_attributes=agent.trace_attributes,
             system_prompt=agent.system_prompt,
-            system_prompt_content=agent._system_prompt_content,
+            system_prompt_content=agent.system_prompt_content,
         )
         with trace_api.use_span(model_invoke_span, end_on_exit=True):
             await agent.hooks.invoke_callbacks_async(
@@ -335,7 +335,7 @@ async def _handle_model_execution(
                     agent.system_prompt,
                     agent.messages,
                     tool_specs,
-                    system_prompt_content=agent._system_prompt_content,
+                    system_prompt_content=agent.system_prompt_content,
                     tool_choice=structured_output_context.tool_choice,
                     invocation_state=invocation_state,
                     model_state=agent._model_state,

tests/strands/agent/test_agent.py

@@ -1140,7 +1140,7 @@ def test_system_prompt_setter_string():
     agent.system_prompt = "updated prompt"
 
     assert agent.system_prompt == "updated prompt"
-    assert agent._system_prompt_content == [{"text": "updated prompt"}]
+    assert agent.system_prompt_content == [{"text": "updated prompt"}]
 
 
 def test_system_prompt_setter_list():
@@ -1151,7 +1151,7 @@ def test_system_prompt_setter_list():
     agent.system_prompt = content_blocks
 
     assert agent.system_prompt == "You are helpful"
-    assert agent._system_prompt_content == content_blocks
+    assert agent.system_prompt_content == content_blocks
 
 
 def test_system_prompt_setter_none():
@@ -1161,7 +1161,7 @@ def test_system_prompt_setter_none():
     agent.system_prompt = None
 
     assert agent.system_prompt is None
-    assert agent._system_prompt_content is None
+    assert agent.system_prompt_content is None
 
 
 @pytest.mark.asyncio
@@ -1964,7 +1964,7 @@ def test_agent_string_system_prompt():
     agent = Agent(system_prompt=system_prompt)
 
     assert agent.system_prompt == system_prompt
-    assert agent._system_prompt_content == [{"text": system_prompt}]
+    assert agent.system_prompt_content == [{"text": system_prompt}]
 
 
 def test_agent_single_text_block_system_prompt():
@@ -1974,7 +1974,7 @@ def test_agent_single_text_block_system_prompt():
     agent = Agent(system_prompt=system_prompt_content)
 
     assert agent.system_prompt == text
-    assert agent._system_prompt_content == system_prompt_content
+    assert agent.system_prompt_content == system_prompt_content
 
 
 def test_agent_multiple_blocks_system_prompt():
@@ -1987,7 +1987,7 @@ def test_agent_multiple_blocks_system_prompt():
     agent = Agent(system_prompt=system_prompt_content)
 
     assert agent.system_prompt == "You are a helpful assistant.\nAdditional instructions."
-    assert agent._system_prompt_content == system_prompt_content
+    assert agent.system_prompt_content == system_prompt_content
 
 
 def test_agent_single_non_text_block_system_prompt():
@@ -1996,23 +1996,23 @@ def test_agent_single_non_text_block_system_prompt():
     agent = Agent(system_prompt=system_prompt_content)
 
     assert agent.system_prompt is None
-    assert agent._system_prompt_content == system_prompt_content
+    assert agent.system_prompt_content == system_prompt_content
 
 
 def test_agent_none_system_prompt():
     """Test initialization with None system prompt."""
     agent = Agent(system_prompt=None)
 
     assert agent.system_prompt is None
-    assert agent._system_prompt_content is None
+    assert agent.system_prompt_content is None
 
 
 def test_agent_empty_list_system_prompt():
     """Test initialization with empty list system prompt."""
     agent = Agent(system_prompt=[])
 
     assert agent.system_prompt is None
-    assert agent._system_prompt_content == []
+    assert agent.system_prompt_content == []
 
 
 def test_agent_backwards_compatibility_string_access():

tests/strands/event_loop/test_event_loop.py

@@ -551,7 +551,7 @@ async def test_event_loop_cycle_creates_spans(
     mock_tracer.start_model_invoke_span.assert_called_once()
     call_kwargs = mock_tracer.start_model_invoke_span.call_args[1]
     assert call_kwargs["system_prompt"] == agent.system_prompt
-    assert call_kwargs["system_prompt_content"] == agent._system_prompt_content
+    assert call_kwargs["system_prompt_content"] == agent.system_prompt_content
     mock_tracer.end_model_invoke_span.assert_called_once()
     mock_tracer.end_event_loop_cycle_span.assert_called_once()
 

tests/strands/vended_plugins/skills/test_agent_skills.py

@@ -38,6 +38,9 @@ def _mock_agent():
         lambda self, value: _set_system_prompt(self, value),
     )
 
+    # Make system_prompt_content property behave like the real Agent
+    type(agent).system_prompt_content = property(lambda self: self._system_prompt_content)
+
     agent.hooks = HookRegistry()
     agent.add_hook = MagicMock(
         side_effect=lambda callback, event_type=None: agent.hooks.add_callback(event_type, callback)
@@ -419,7 +422,7 @@ def test_uses_public_system_prompt_setter(self):
 
         # The public setter should have been used, so _system_prompt_content
         # should be consistent with _system_prompt
-        assert agent._system_prompt_content == [{"text": agent._system_prompt}]
+        assert agent.system_prompt_content == [{"text": agent._system_prompt}]
 
     def test_warns_when_previous_xml_not_found(self, caplog):
         """Test that a warning is logged when the previously injected XML is missing from the prompt."""