Context Summarization

Automatically compress conversation history to manage token usage in long-running conversations

Overview

In long-running voice AI conversations, context grows with every exchange. This increases token usage, raises costs, and can eventually hit context window limits. Pipecat includes built-in context summarization that automatically compresses older conversation history while preserving recent messages and important context.

How It Works

Context summarization automatically triggers when either condition is met:

• Token limit reached: Context size exceeds max_context_tokens (estimated using ~4 characters per token)
• Message count reached: Number of new messages exceeds max_unsummarized_messages

You can disable either threshold by setting it to None, but at least one must remain active. Summarization always generates a summary and cannot be reduced to pure truncation.

When triggered, the system:

1. Sends a LLMContextSummaryRequestFrame to the LLM service
2. The LLM generates a concise summary of older messages
3. Context is reconstructed as: [system_message (if present)] + [summary] + [recent_messages]
4. Incomplete function call sequences and recent messages are preserved

Context summarization is asynchronous and happens in the background without blocking the pipeline. The system uses request IDs to match summary requests with results and handles interruptions gracefully.

Enabling Context Summarization

Enable summarization by setting enable_auto_context_summarization=True in LLMAssistantAggregatorParams:

from pipecat.processors.aggregators.llm_response_universal import (
    LLMAssistantAggregatorParams,
    LLMContextAggregatorPair,
)

# Create aggregators with summarization enabled
user_aggregator, assistant_aggregator = LLMContextAggregatorPair(
    context,
    assistant_params=LLMAssistantAggregatorParams(
        enable_auto_context_summarization=True,
    ),
)

Automatic summarization is disabled by default (enable_auto_context_summarization=False). When enabled with the default configuration, summarization triggers at 8000 estimated tokens or after 20 new messages, whichever comes first.

Customizing Behavior

Use LLMAutoContextSummarizationConfig and LLMContextSummaryConfig to tune the summarization triggers and output:

from pipecat.utils.context.llm_context_summarization import (
    LLMAutoContextSummarizationConfig,
    LLMContextSummaryConfig,
)

user_aggregator, assistant_aggregator = LLMContextAggregatorPair(
    context,
    assistant_params=LLMAssistantAggregatorParams(
        enable_auto_context_summarization=True,
        auto_context_summarization_config=LLMAutoContextSummarizationConfig(
            max_context_tokens=4000,           # Trigger at 4000 tokens
            max_unsummarized_messages=10,      # Or trigger after 10 new messages
            summary_config=LLMContextSummaryConfig(
                target_context_tokens=3000,    # Target summary size
                min_messages_after_summary=2,  # Keep last 2 messages uncompressed
            ),
        ),
    ),
)

See the reference page for all available configuration parameters.

What Gets Preserved

Context summarization intelligently preserves:

• System messages: If the first message (messages[0]) is a system message, it is preserved as the initial system prompt. Mid-conversation system messages (e.g., idle notifications or context injections) are treated as regular messages and included in the summarization range. When using system_instruction in LLM Settings instead, the system prompt is not part of the context messages and is automatically prepended by the service on each request, so there is nothing to preserve in the context.
• Recent messages: The last N messages stay uncompressed (configured by min_messages_after_summary)
• Function call sequences: Incomplete function call/result pairs are not split during summarization
• Developer messages are NOT preserved: Developer messages ("role": "developer") are included in the summarization range like any other message and may be compressed or dropped. If instructions need to survive summarization, use system_instruction instead.

Custom Summarization Prompts

You can override the default summarization prompt to control how the LLM generates summaries:

custom_prompt = """Summarize this conversation concisely.
Focus on: key decisions, user preferences, and action items.
Keep the summary under {target_tokens} tokens."""

config = LLMAutoContextSummarizationConfig(
    summary_config=LLMContextSummaryConfig(
        summarization_prompt=custom_prompt,
    ),
)

When no custom prompt is provided, Pipecat uses a built-in prompt that instructs the LLM to create a concise summary preserving key information, user preferences, and conversation flow.

Dedicated Summarization LLM

By default, summarization uses the same LLM service that handles conversation. You can route summarization to a separate, cheaper model by setting the llm field:

from pipecat.services.google import GoogleLLMService

# Use a fast/cheap model for summarization
summarization_llm = GoogleLLMService(
    api_key=os.getenv("GOOGLE_API_KEY"),
    model="gemini-2.5-flash",
)

config = LLMAutoContextSummarizationConfig(
    summary_config=LLMContextSummaryConfig(
        llm=summarization_llm,
    ),
)

When a dedicated LLM is configured, summarization requests bypass the pipeline entirely and call the dedicated service directly, so the primary conversation LLM is never interrupted.

On-Demand Summarization

In addition to automatic summarization, you can trigger context summarization on demand by pushing an LLMSummarizeContextFrame into the pipeline. This is useful when you want to give users explicit control over when summarization happens — for example, via a function call tool.

from pipecat.frames.frames import LLMSummarizeContextFrame
from pipecat.services.llm_service import FunctionCallParams

async def summarize_conversation(params: FunctionCallParams):
    """Summarize and compress the conversation history. Call this when the user asks you to summarize the conversation or when you want to free up context space."""
    await params.result_callback({"status": "summarization_requested"})
    await params.llm.queue_frame(LLMSummarizeContextFrame())

Above, summarize_conversation is a direct function. List it in the context’s tools so the LLM can invoke it when the user asks to summarize:

context = LLMContext(messages, tools=[summarize_conversation])

On-demand summarization works even when enable_auto_context_summarization is False — the summarizer is always created internally to handle manually pushed frames. You can also pass a per-request LLMContextSummaryConfig to override the default settings:

from pipecat.utils.context.llm_context_summarization import LLMContextSummaryConfig

await llm.queue_frame(
    LLMSummarizeContextFrame(
        config=LLMContextSummaryConfig(
            target_context_tokens=2000,
            min_messages_after_summary=2,
        )
    )
)

See the complete example for a full working implementation.

Observability

The summarizer emits an on_summary_applied event after each successful summarization, providing message count metrics:

from pipecat.processors.aggregators.llm_context_summarizer import SummaryAppliedEvent

summarizer = assistant_aggregator._summarizer
if summarizer:

    @summarizer.event_handler("on_summary_applied")
    async def on_summary_applied(summarizer, event: SummaryAppliedEvent):
        logger.info(
            f"Context summarized: {event.original_message_count} messages -> "
            f"{event.new_message_count} messages "
            f"({event.summarized_message_count} summarized, "
            f"{event.preserved_message_count} preserved)"
        )

Next Steps

Context Summarization Reference

Full reference for configuration parameters, events, and classes.

Context Management

Learn how Pipecat manages conversation context in pipelines.