diff --git a/python/semantic_kernel/contents/history_reducer/chat_history_reducer_utils.py b/python/semantic_kernel/contents/history_reducer/chat_history_reducer_utils.py
index 459eac6a6e52..c0ed3488fcf5 100644
--- a/python/semantic_kernel/contents/history_reducer/chat_history_reducer_utils.py
+++ b/python/semantic_kernel/contents/history_reducer/chat_history_reducer_utils.py
@@ -66,6 +66,7 @@ def locate_safe_reduction_index(
     target_count: int,
     threshold_count: int = 0,
     offset_count: int = 0,
+    has_system_message: bool = False,
 ) -> int | None:
     """Identify the index of the first message at or beyond the specified target_count.
 
@@ -83,11 +84,27 @@ def locate_safe_reduction_index(
         threshold_count: The threshold beyond target_count required to trigger reduction.
                          If total messages <= (target_count + threshold_count), no reduction occurs.
         offset_count: Optional number of messages to skip at the start (e.g. existing summary messages).
+        has_system_message: Whether the history contains a system message that will be preserved
+                           separately. When True, the target_count is adjusted to account for the
+                           system message being re-added after reduction.
 
     Returns:
         The index that identifies the starting point for a reduced history that does not orphan
         sensitive content. Returns None if reduction is not needed.
     """
+    # Adjust target_count to account for the system message that will be preserved separately.
+    # This matches the .NET SDK behavior.
+    if has_system_message:
+        target_count -= 1
+        if target_count <= 0:
+            logger.warning(
+                "target_count after accounting for system message is %d; reduction will keep only the system message.",
+                target_count,
+            )
+            # Reduce to just the system message — return index past all non-system messages.
+            # The caller will prepend the system message to the empty/minimal tail.
+            return len(history)
+
     total_count = len(history)
     threshold_index = total_count - (threshold_count or 0) - target_count
     if threshold_index <= offset_count:
diff --git a/python/semantic_kernel/contents/history_reducer/chat_history_summarization_reducer.py b/python/semantic_kernel/contents/history_reducer/chat_history_summarization_reducer.py
index e01594f1e0e4..3b8d2db82acf 100644
--- a/python/semantic_kernel/contents/history_reducer/chat_history_summarization_reducer.py
+++ b/python/semantic_kernel/contents/history_reducer/chat_history_summarization_reducer.py
@@ -26,6 +26,7 @@
     locate_safe_reduction_index,
     locate_summarization_boundary,
 )
+from semantic_kernel.contents.utils.author_role import AuthorRole
 from semantic_kernel.exceptions.content_exceptions import ChatHistoryReducerException
 from semantic_kernel.utils.feature_stage_decorator import experimental
 
@@ -89,6 +90,21 @@ async def reduce(self) -> Self | None:
 
         logger.info("Performing chat history summarization check...")
 
+        # Preserve system/developer messages so they are not lost during summarization.
+        # This matches the .NET SDK behavior and the truncation reducer.
+        # Only the first system/developer message is preserved; this mirrors .NET semantics.
+        # Exclude summary messages (which may have SYSTEM role) — they are generated content,
+        # not original system prompts.
+        system_message_index = next(
+            (
+                i
+                for i, msg in enumerate(history)
+                if msg.role in (AuthorRole.SYSTEM, AuthorRole.DEVELOPER) and not msg.metadata.get(SUMMARY_METADATA_KEY)
+            ),
+            -1,
+        )
+        system_message = history[system_message_index] if system_message_index >= 0 else None
+
         # 1. Identify where existing summary messages end
         insertion_point = locate_summarization_boundary(history)
         if insertion_point == len(history):
@@ -96,12 +112,19 @@ async def reduce(self) -> Self | None:
             logger.warning("All messages are summaries, forcing boundary to 0.")
             insertion_point = 0
 
+        # Only adjust target_count if the system message would be truncated away.
+        # If the system message is already in the retained portion, no adjustment needed.
+        system_would_be_truncated = (
+            system_message is not None and system_message_index < len(history) - self.target_count
+        )
+
         # 2. Locate the safe reduction index
         truncation_index = locate_safe_reduction_index(
             history,
             self.target_count,
             self.threshold_count,
             offset_count=insertion_point,
+            has_system_message=system_would_be_truncated,
         )
         if truncation_index is None:
             logger.info("No valid truncation index found.")
@@ -138,7 +161,13 @@ async def reduce(self) -> Self | None:
                 keep_existing_summaries = history[:insertion_point]
 
             remainder = history[truncation_index:]
+
+            # Prepend the system/developer message if it was summarized away.
+            # Use identity comparison to avoid false matches from value-equal messages.
             new_history = [*keep_existing_summaries, summary_msg, *remainder]
+            if system_message is not None and not any(m is system_message for m in new_history):
+                new_history = [system_message, *new_history]
+
             self.messages = new_history
 
             return self
@@ -151,8 +180,6 @@ async def reduce(self) -> Self | None:
 
     async def _summarize(self, messages: list[ChatMessageContent]) -> ChatMessageContent | None:
         """Use the ChatCompletion service to generate a single summary message."""
-        from semantic_kernel.contents.utils.author_role import AuthorRole
-
         chat_history = ChatHistory(messages=messages)
         execution_settings = self.execution_settings or self.service.get_prompt_execution_settings_from_settings(
             PromptExecutionSettings()
diff --git a/python/semantic_kernel/contents/history_reducer/chat_history_truncation_reducer.py b/python/semantic_kernel/contents/history_reducer/chat_history_truncation_reducer.py
index 32c848a098d7..0d0810feb8df 100644
--- a/python/semantic_kernel/contents/history_reducer/chat_history_truncation_reducer.py
+++ b/python/semantic_kernel/contents/history_reducer/chat_history_truncation_reducer.py
@@ -15,9 +15,9 @@
 
 from semantic_kernel.contents.history_reducer.chat_history_reducer import ChatHistoryReducer
 from semantic_kernel.contents.history_reducer.chat_history_reducer_utils import (
-    extract_range,
     locate_safe_reduction_index,
 )
+from semantic_kernel.contents.utils.author_role import AuthorRole
 from semantic_kernel.utils.feature_stage_decorator import experimental
 
 logger = logging.getLogger(__name__)
@@ -45,7 +45,28 @@ async def reduce(self) -> Self | None:
 
         logger.info("Performing chat history truncation check...")
 
-        truncation_index = locate_safe_reduction_index(history, self.target_count, self.threshold_count)
+        # Preserve system/developer messages so they are not lost during truncation.
+        # This matches the .NET SDK behavior where system messages are always retained.
+        # Only the first system/developer message is preserved; this mirrors .NET semantics.
+        system_message_index = next(
+            (i for i, msg in enumerate(history) if msg.role in (AuthorRole.SYSTEM, AuthorRole.DEVELOPER)),
+            -1,
+        )
+        system_message = history[system_message_index] if system_message_index >= 0 else None
+
+        # Only adjust target_count if the system message would be truncated away
+        # (i.e., it falls before the naive tail). If the system message is already in the
+        # retained portion, no adjustment is needed — it naturally occupies a slot.
+        system_would_be_truncated = (
+            system_message is not None and system_message_index < len(history) - self.target_count
+        )
+
+        truncation_index = locate_safe_reduction_index(
+            history,
+            self.target_count,
+            self.threshold_count,
+            has_system_message=system_would_be_truncated,
+        )
         if truncation_index is None:
             logger.info(
                 f"No truncation index found. Target count: {self.target_count}, Threshold: {self.threshold_count}"
@@ -53,7 +74,13 @@ async def reduce(self) -> Self | None:
             return None
 
         logger.info(f"Truncating history to {truncation_index} messages.")
-        truncated_list = extract_range(history, start=truncation_index)
+        truncated_list = history[truncation_index:]
+
+        # Prepend the system/developer message if it was truncated away.
+        # Use identity comparison (is) to avoid false matches from value-equal messages.
+        if system_message is not None and all(msg is not system_message for msg in truncated_list):
+            truncated_list = [system_message, *truncated_list]
+
         self.messages = truncated_list
         return self
 
diff --git a/python/tests/unit/contents/test_chat_history_summarization_reducer.py b/python/tests/unit/contents/test_chat_history_summarization_reducer.py
index c61d044a9811..3914128ef4b5 100644
--- a/python/tests/unit/contents/test_chat_history_summarization_reducer.py
+++ b/python/tests/unit/contents/test_chat_history_summarization_reducer.py
@@ -226,3 +226,89 @@ async def test_summarization_reducer_private_summarize(mock_service):
     actual_summary = await reducer._summarize(chat_messages)
     assert actual_summary is not None, "We should get a summary message back."
     assert actual_summary.content == "Mock Summary", "We expect the mock summary content."
+
+
+async def test_summarization_preserves_system_message(mock_service):
+    """Verify that the summarization reducer preserves system messages."""
+    messages = [
+        ChatMessageContent(role=AuthorRole.SYSTEM, content="Important system prompt"),
+        ChatMessageContent(role=AuthorRole.USER, content="User says hello"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant responds"),
+        ChatMessageContent(role=AuthorRole.USER, content="User says more"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant responds again"),
+        ChatMessageContent(role=AuthorRole.USER, content="User says even more"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant responds yet again"),
+    ]
+
+    reducer = ChatHistorySummarizationReducer(service=mock_service, target_count=3, threshold_count=0)
+    reducer.messages = messages
+
+    summary_content = ChatMessageContent(role=AuthorRole.ASSISTANT, content="Summary of conversation.")
+    mock_service.get_chat_message_content.return_value = summary_content
+    mock_service.get_prompt_execution_settings_from_settings.return_value = PromptExecutionSettings()
+
+    result = await reducer.reduce()
+    assert result is not None
+    # System message must be preserved
+    roles = [msg.role for msg in result.messages]
+    assert AuthorRole.SYSTEM in roles, "System message was lost during summarization"
+    # System message should be first
+    assert result.messages[0].role == AuthorRole.SYSTEM
+    assert result.messages[0].content == "Important system prompt"
+
+
+async def test_summarization_does_not_preserve_summary_system_message(mock_service):
+    """A prior summary with SYSTEM role should NOT be treated as the system prompt to preserve."""
+    summary_sys = ChatMessageContent(
+        role=AuthorRole.SYSTEM, content="Previous summary", metadata={SUMMARY_METADATA_KEY: True}
+    )
+    messages = [
+        summary_sys,
+        ChatMessageContent(role=AuthorRole.USER, content="User says hello"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant responds"),
+        ChatMessageContent(role=AuthorRole.USER, content="User says more"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant responds again"),
+        ChatMessageContent(role=AuthorRole.USER, content="User says even more"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant responds yet again"),
+    ]
+
+    reducer = ChatHistorySummarizationReducer(service=mock_service, target_count=3, threshold_count=0)
+    reducer.messages = messages
+
+    summary_content = ChatMessageContent(role=AuthorRole.ASSISTANT, content="New summary.")
+    mock_service.get_chat_message_content.return_value = summary_content
+    mock_service.get_prompt_execution_settings_from_settings.return_value = PromptExecutionSettings()
+
+    result = await reducer.reduce()
+    assert result is not None
+    # The old summary-system message should NOT be preserved as a "system prompt"
+    # It should be replaced by the new summary
+    for msg in result.messages:
+        if msg.role == AuthorRole.SYSTEM:
+            assert msg.metadata.get(SUMMARY_METADATA_KEY) is not True or msg is not summary_sys
+
+
+async def test_summarization_preserves_developer_message(mock_service):
+    """Verify that developer messages are preserved during summarization."""
+    messages = [
+        ChatMessageContent(role=AuthorRole.DEVELOPER, content="Developer instructions"),
+        ChatMessageContent(role=AuthorRole.USER, content="User says hello"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant responds"),
+        ChatMessageContent(role=AuthorRole.USER, content="User says more"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant responds again"),
+        ChatMessageContent(role=AuthorRole.USER, content="User says even more"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant responds yet again"),
+    ]
+
+    reducer = ChatHistorySummarizationReducer(service=mock_service, target_count=3, threshold_count=0)
+    reducer.messages = messages
+
+    summary_content = ChatMessageContent(role=AuthorRole.ASSISTANT, content="Summary of conversation.")
+    mock_service.get_chat_message_content.return_value = summary_content
+    mock_service.get_prompt_execution_settings_from_settings.return_value = PromptExecutionSettings()
+
+    result = await reducer.reduce()
+    assert result is not None
+    # Developer message must be preserved
+    assert result.messages[0].role == AuthorRole.DEVELOPER
+    assert result.messages[0].content == "Developer instructions"
diff --git a/python/tests/unit/contents/test_chat_history_truncation_reducer.py b/python/tests/unit/contents/test_chat_history_truncation_reducer.py
index 57b4f33ede48..de866708b686 100644
--- a/python/tests/unit/contents/test_chat_history_truncation_reducer.py
+++ b/python/tests/unit/contents/test_chat_history_truncation_reducer.py
@@ -1,10 +1,13 @@
 # Copyright (c) Microsoft. All rights reserved.
 
+import logging
+
 import pytest
 
 from semantic_kernel.contents.chat_message_content import ChatMessageContent
 from semantic_kernel.contents.function_call_content import FunctionCallContent
 from semantic_kernel.contents.function_result_content import FunctionResultContent
+from semantic_kernel.contents.history_reducer.chat_history_reducer_utils import locate_safe_reduction_index
 from semantic_kernel.contents.history_reducer.chat_history_truncation_reducer import ChatHistoryTruncationReducer
 from semantic_kernel.contents.utils.author_role import AuthorRole
 
@@ -83,11 +86,13 @@ async def test_truncation_reducer_truncation(chat_messages):
     reducer = ChatHistoryTruncationReducer(target_count=2)
     reducer.messages = chat_messages
     result = await reducer.reduce()
-    # We expect only 2 messages remain after truncation
+    # We expect 2 messages: system message is preserved + 1 conversation message
+    # (target_count=2 includes the system message, matching .NET SDK behavior)
     assert result is not None
     assert len(result) == 2
-    # They should be the last 4 messages while tool result is not orphaned
-    assert result[0] == chat_messages[-2]
+    # System message should be first, followed by the last conversation message
+    assert result[0] == chat_messages[0]  # System message preserved
+    assert result[0].role == AuthorRole.SYSTEM
     assert result[1] == chat_messages[-1]
 
 
@@ -96,12 +101,206 @@ async def test_truncation_reducer_truncation_with_tools(chat_messages_with_tools
     reducer = ChatHistoryTruncationReducer(target_count=3, threshold_count=0)
     reducer.messages = chat_messages_with_tools
     result = await reducer.reduce()
-    # We expect 4 messages remain after truncation
-    # Tool results are not orphaned, so we expect to keep them
+    # We expect 3 messages: system message + last 2 conversation messages
+    # (target_count=3 includes the system message, matching .NET SDK behavior)
+    assert result is not None
+    assert len(result) == 3
+    # System message preserved, followed by last user-assistant pair
+    assert result[0] == chat_messages_with_tools[0]  # System message
+    assert result[0].role == AuthorRole.SYSTEM
+    assert result[1] == chat_messages_with_tools[-2]  # User message 2
+    assert result[2] == chat_messages_with_tools[-1]  # Assistant message 2
+
+
+async def test_truncation_preserves_system_message():
+    """Verify that the system message is preserved after truncation (issue #12612)."""
+    reducer = ChatHistoryTruncationReducer(
+        target_count=2,
+        system_message="a system message",
+    )
+    reducer.add_message(ChatMessageContent(role=AuthorRole.USER, content="user prompt 1"))
+    reducer.add_message(ChatMessageContent(role=AuthorRole.ASSISTANT, content="response 1"))
+    reducer.add_message(ChatMessageContent(role=AuthorRole.USER, content="user prompt 2"))
+    reducer.add_message(ChatMessageContent(role=AuthorRole.ASSISTANT, content="response 2"))
+    reducer.add_message(ChatMessageContent(role=AuthorRole.USER, content="user prompt 3"))
+    reducer.add_message(ChatMessageContent(role=AuthorRole.ASSISTANT, content="response 3"))
+    reducer.add_message(ChatMessageContent(role=AuthorRole.USER, content="user prompt 4"))
+    reducer.add_message(ChatMessageContent(role=AuthorRole.ASSISTANT, content="response 4"))
+
+    result = await reducer.reduce()
+    assert result is not None
+
+    # System message must be present after reduction
+    roles = [msg.role for msg in result.messages]
+    assert AuthorRole.SYSTEM in roles, "System message was deleted by the history reducer"
+    assert result.messages[0].role == AuthorRole.SYSTEM
+    assert result.messages[0].content == "a system message"
+
+
+async def test_truncation_preserves_developer_message():
+    """Verify that developer messages are preserved after truncation."""
+    msgs = [
+        ChatMessageContent(role=AuthorRole.DEVELOPER, content="Developer instructions."),
+        ChatMessageContent(role=AuthorRole.USER, content="User message 1"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant message 1"),
+        ChatMessageContent(role=AuthorRole.USER, content="User message 2"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant message 2"),
+    ]
+    reducer = ChatHistoryTruncationReducer(target_count=2)
+    reducer.messages = msgs
+    result = await reducer.reduce()
+    assert result is not None
+    assert len(result) == 2
+    # Developer message should be first
+    assert result[0].role == AuthorRole.DEVELOPER
+    assert result[0].content == "Developer instructions."
+
+
+async def test_truncation_target_count_1_with_system_message():
+    """With target_count=1 and a system message, reduce to just the system message."""
+    reducer = ChatHistoryTruncationReducer(target_count=1, system_message="System prompt")
+    reducer.add_message(ChatMessageContent(role=AuthorRole.USER, content="Hello"))
+    reducer.add_message(ChatMessageContent(role=AuthorRole.ASSISTANT, content="Hi"))
+    reducer.add_message(ChatMessageContent(role=AuthorRole.USER, content="How are you?"))
+    reducer.add_message(ChatMessageContent(role=AuthorRole.ASSISTANT, content="Good"))
+
+    result = await reducer.reduce()
+    # Must reduce — history has 5 messages but target is 1
+    assert result is not None
+    # Should contain only the system message
+    assert len(result.messages) == 1
+    assert result.messages[0].role == AuthorRole.SYSTEM
+    assert result.messages[0].content == "System prompt"
+
+
+async def test_truncation_without_system_message():
+    """Verify truncation works correctly when there is no system message."""
+    msgs = [
+        ChatMessageContent(role=AuthorRole.USER, content="User message 1"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant message 1"),
+        ChatMessageContent(role=AuthorRole.USER, content="User message 2"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Assistant message 2"),
+    ]
+    reducer = ChatHistoryTruncationReducer(target_count=2)
+    reducer.messages = msgs
+    result = await reducer.reduce()
+    assert result is not None
+    assert len(result) == 2
+    assert result[0] == msgs[-2]
+    assert result[1] == msgs[-1]
+
+
+# --- Direct tests for locate_safe_reduction_index ---
+
+
+def test_locate_safe_reduction_index_with_system_message():
+    """Test locate_safe_reduction_index adjusts target_count for system message."""
+    history = [
+        ChatMessageContent(role=AuthorRole.SYSTEM, content="System"),
+        ChatMessageContent(role=AuthorRole.USER, content="User 1"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Asst 1"),
+        ChatMessageContent(role=AuthorRole.USER, content="User 2"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Asst 2"),
+    ]
+    # target_count=3 with system message → adjusted to 2, so truncation_index = 5 - 2 = 3
+    index = locate_safe_reduction_index(history, target_count=3, has_system_message=True)
+    assert index is not None
+    assert index == 3  # Keep last 2 messages, system message re-added by caller
+
+
+def test_locate_safe_reduction_index_without_system_message():
+    """Test locate_safe_reduction_index without system message flag."""
+    history = [
+        ChatMessageContent(role=AuthorRole.USER, content="User 1"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Asst 1"),
+        ChatMessageContent(role=AuthorRole.USER, content="User 2"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Asst 2"),
+    ]
+    # target_count=2, no system message → truncation_index = 4 - 2 = 2
+    index = locate_safe_reduction_index(history, target_count=2)
+    assert index is not None
+    assert index == 2
+
+
+def test_locate_safe_reduction_index_target_zero_returns_len(caplog):
+    """When target_count=1 + has_system_message → adjusted to 0 → returns len(history)."""
+    history = [
+        ChatMessageContent(role=AuthorRole.SYSTEM, content="System"),
+        ChatMessageContent(role=AuthorRole.USER, content="User 1"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Asst 1"),
+    ]
+    with caplog.at_level(logging.WARNING):
+        index = locate_safe_reduction_index(history, target_count=1, has_system_message=True)
+    assert index == len(history)
+    assert "target_count after accounting for system message is 0" in caplog.text
+
+
+def test_locate_safe_reduction_index_no_reduction_needed():
+    """When total <= target + threshold, returns None (no reduction needed)."""
+    history = [
+        ChatMessageContent(role=AuthorRole.USER, content="User 1"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Asst 1"),
+    ]
+    index = locate_safe_reduction_index(history, target_count=2, threshold_count=0)
+    assert index is None
+
+
+# --- Multiple system/developer messages ---
+
+
+async def test_truncation_multiple_system_messages():
+    """Only the first system/developer message is preserved; others may be lost."""
+    msgs = [
+        ChatMessageContent(role=AuthorRole.SYSTEM, content="System prompt 1"),
+        ChatMessageContent(role=AuthorRole.DEVELOPER, content="Developer instructions"),
+        ChatMessageContent(role=AuthorRole.USER, content="User 1"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Asst 1"),
+        ChatMessageContent(role=AuthorRole.USER, content="User 2"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Asst 2"),
+    ]
+    reducer = ChatHistoryTruncationReducer(target_count=2)
+    reducer.messages = msgs
+    result = await reducer.reduce()
+    assert result is not None
+    # First system message is preserved
+    assert result[0].role == AuthorRole.SYSTEM
+    assert result[0].content == "System prompt 1"
+
+
+# --- System message in retained tail (not truncated away) ---
+
+
+async def test_truncation_system_message_in_retained_tail():
+    """When system message falls within the retained portion, it is not duplicated."""
+    msgs = [
+        ChatMessageContent(role=AuthorRole.USER, content="User 1"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Asst 1"),
+        ChatMessageContent(role=AuthorRole.USER, content="User 2"),
+        ChatMessageContent(role=AuthorRole.SYSTEM, content="Late system msg"),
+        ChatMessageContent(role=AuthorRole.ASSISTANT, content="Asst 2"),
+    ]
+    # target_count=3, system at index 3 is within the naive tail (indices 2..4).
+    # No target_count adjustment needed — system message stays in its natural position.
+    reducer = ChatHistoryTruncationReducer(target_count=3)
+    reducer.messages = msgs
+    result = await reducer.reduce()
+    assert result is not None
+    # Should have exactly target_count messages, with system message not duplicated
+    assert len(result.messages) == 3
+    system_msgs = [m for m in result.messages if m.role == AuthorRole.SYSTEM]
+    assert len(system_msgs) == 1
+
+
+# --- Warning log test ---
+
+
+async def test_truncation_target_1_logs_warning(caplog):
+    """Verify a warning is logged when target_count=1 with a system message."""
+    reducer = ChatHistoryTruncationReducer(target_count=1, system_message="System")
+    reducer.add_message(ChatMessageContent(role=AuthorRole.USER, content="Hello"))
+    reducer.add_message(ChatMessageContent(role=AuthorRole.ASSISTANT, content="Hi"))
+
+    with caplog.at_level(logging.WARNING):
+        result = await reducer.reduce()
     assert result is not None
-    assert len(result) == 4
-    # They should be the last 4 messages
-    assert result[0] == chat_messages_with_tools[-4]
-    assert result[1] == chat_messages_with_tools[-3]
-    assert result[2] == chat_messages_with_tools[-2]
-    assert result[3] == chat_messages_with_tools[-1]
+    assert "target_count after accounting for system message is 0" in caplog.text