## Summary `ChatHistoryTruncationReducer.reduce()` silently deletes system/developer messages when truncating chat history. This is because it calls `extract_range()`, which unconditionally filters out system/developer messages — a function designed for the summarization use case, not truncation. Fixes #12612. ## Approach Port the .NET SDK fix (PR #10344) to Python: 1. Detect the first system/developer message before truncation 2. Pass `has_system_message=True` to `locate_safe_reduction_index` so `target_count` accounts for the preserved message (matches .NET's `targetCount -= hasSystemMessage ? 1 : 0`) 3. Use a simple `history[truncation_index:]` slice instead of `extract_range` (which strips system messages) 4. Prepend the system message if it was truncated away Also adds a guard for `target_count <= 0` after the system message adjustment to prevent `IndexError` when `target_count=1`. ## Changes | File | Change | |------|--------| | `chat_history_reducer_utils.py` | Add `has_system_message` parameter, adjust `target_count`, guard against `<= 0` | | `chat_history_truncation_reducer.py` | Detect system message, bypass `extract_range`, prepend if truncated | | `test_chat_history_truncation_reducer.py` | Update 2 existing tests + 4 new tests (system, developer, no-system, target_count=1) | ## Note The summarization reducer (`ChatHistorySummarizationReducer`) has the same bug — it also uses `extract_range` and loses system messages during summarization. The .NET summarization reducer preserves system messages via `AssemblySummarizedHistory`. This should be addressed in a follow-up PR to keep this change focused. ## Test plan - [x] 11/11 truncation reducer tests pass (was 7, now 11) - [x] 9/9 utils tests pass (no regressions from new parameter) - [x] 11/11 summarization reducer tests pass (unaffected) - [x] Reproduces and fixes the exact scenario from #12612 - [x] Edge case: `target_count=1` with system message does not crash --------- Co-authored-by: Claude Opus 4.6 <[email protected]> Co-authored-by: Evan Mattson <[email protected]>
Get Started with Semantic Kernel Python
Highlights
- Flexible Agent Framework: build, orchestrate, and deploy AI agents and multi-agent systems
- Multi-Agent Systems: Model workflows and collaboration between AI specialists
- Plugin Ecosystem: Extend with Python, OpenAPI, Model Context Protocol (MCP), and more
- LLM Support: OpenAI, Azure OpenAI, Hugging Face, Mistral, Google AI, ONNX, Ollama, NVIDIA NIM, and others
- Vector DB Support: Azure AI Search, Elasticsearch, Chroma, and more
- Process Framework: Build structured business processes with workflow modeling
- Multimodal: Text, vision, audio
Quick Install
pip install --upgrade semantic-kernel
# Optional: Add integrations
pip install --upgrade semantic-kernel[hugging_face]
pip install --upgrade semantic-kernel[all]
Supported Platforms:
- Python: 3.10+
- OS: Windows, macOS, Linux
1. Setup API Keys
Set as environment variables, or create a .env file at your project root:
OPENAI_API_KEY=sk-...
OPENAI_CHAT_MODEL_ID=...
...
AZURE_OPENAI_API_KEY=...
AZURE_OPENAI_ENDPOINT=...
AZURE_OPENAI_CHAT_DEPLOYMENT_NAME=...
...
You can also override environment variables by explicitly passing configuration parameters to the AI service constructor:
chat_service = AzureChatCompletion(
api_key=...,
endpoint=...,
deployment_name=...,
api_version=...,
)
See the following setup guide for more information.
2. Use the Kernel for Prompt Engineering
Create prompt functions and invoke them via the Kernel:
import asyncio
from semantic_kernel import Kernel
from semantic_kernel.connectors.ai.open_ai import OpenAIChatCompletion
from semantic_kernel.functions import KernelArguments
kernel = Kernel()
kernel.add_service(OpenAIChatCompletion())
prompt = """
1) A robot may not injure a human being...
2) A robot must obey orders given it by human beings...
3) A robot must protect its own existence...
Give me the TLDR in exactly {{$num_words}} words."""
async def main():
result = await kernel.invoke_prompt(prompt, arguments=KernelArguments(num_words=5))
print(result)
asyncio.run(main())
# Output: Protect humans, obey, self-preserve, prioritized.
3. Directly Use AI Services (No Kernel Required)
You can use the AI service classes directly for advanced workflows:
import asyncio
import asyncio
from semantic_kernel.connectors.ai.open_ai import OpenAIChatCompletion, OpenAIChatPromptExecutionSettings
from semantic_kernel.contents import ChatHistory
async def main():
service = OpenAIChatCompletion()
settings = OpenAIChatPromptExecutionSettings()
chat_history = ChatHistory(system_message="You are a helpful assistant.")
chat_history.add_user_message("Write a haiku about Semantic Kernel.")
response = await service.get_chat_message_content(chat_history=chat_history, settings=settings)
print(response.content)
"""
Output:
Thoughts weave through context,
Semantic threads interlace—
Kernel sparks meaning.
"""
asyncio.run(main())
4. Build an Agent with Plugins and Tools
Add Python functions as plugins or Pydantic models as structured outputs;
Enhance your agent with custom tools (plugins) and structured output:
import asyncio
from typing import Annotated
from pydantic import BaseModel
from semantic_kernel.agents import ChatCompletionAgent
from semantic_kernel.connectors.ai.open_ai import AzureChatCompletion, OpenAIChatPromptExecutionSettings
from semantic_kernel.functions import kernel_function, KernelArguments
class MenuPlugin:
@kernel_function(description="Provides a list of specials from the menu.")
def get_specials(self) -> Annotated[str, "Returns the specials from the menu."]:
return """
Special Soup: Clam Chowder
Special Salad: Cobb Salad
Special Drink: Chai Tea
"""
@kernel_function(description="Provides the price of the requested menu item.")
def get_item_price(
self, menu_item: Annotated[str, "The name of the menu item."]
) -> Annotated[str, "Returns the price of the menu item."]:
return "$9.99"
class MenuItem(BaseModel):
# Used for structured outputs
price: float
name: str
async def main():
# Configure structured outputs format
settings = OpenAIChatPromptExecutionSettings()
settings.response_format = MenuItem
# Create agent with plugin and settings
agent = ChatCompletionAgent(
service=AzureChatCompletion(),
name="SK-Assistant",
instructions="You are a helpful assistant.",
plugins=[MenuPlugin()],
arguments=KernelArguments(settings)
)
response = await agent.get_response("What is the price of the soup special?")
print(response.content)
# Output:
# The price of the Clam Chowder, which is the soup special, is $9.99.
asyncio.run(main())
You can explore additional getting started agent samples here.
5. Multi-Agent Orchestration
Coordinate a group of agents to iteratively solve a problem or refine content together:
import asyncio
from semantic_kernel.agents import ChatCompletionAgent, GroupChatOrchestration, RoundRobinGroupChatManager
from semantic_kernel.agents.runtime import InProcessRuntime
from semantic_kernel.connectors.ai.open_ai import AzureChatCompletion
def get_agents():
return [
ChatCompletionAgent(
name="Writer",
instructions="You are a creative content writer. Generate and refine slogans based on feedback.",
service=AzureChatCompletion(),
),
ChatCompletionAgent(
name="Reviewer",
instructions="You are a critical reviewer. Provide detailed feedback on proposed slogans.",
service=AzureChatCompletion(),
),
]
async def main():
agents = get_agents()
group_chat = GroupChatOrchestration(
members=agents,
manager=RoundRobinGroupChatManager(max_rounds=5),
)
runtime = InProcessRuntime()
runtime.start()
result = await group_chat.invoke(
task="Create a slogan for a new electric SUV that is affordable and fun to drive.",
runtime=runtime,
)
value = await result.get()
print(f"Final Slogan: {value}")
# Example Output:
# Final Slogan: "Feel the Charge: Adventure Meets Affordability in Your New Electric SUV!"
await runtime.stop_when_idle()
if __name__ == "__main__":
asyncio.run(main())
For orchestration-focused examples, see these orchestration samples.
More Examples & Notebooks
- Getting Started with Agents: Practical agent orchestration and tool use
- Getting Started with Processes: Modeling structured workflows with the Process framework
- Concept Samples: Advanced scenarios, integrations, and SK patterns
- Getting Started Notebooks: Interactive Python notebooks for rapid experimentation