langchain-collapse

Preventive context management for LangChain agents.

When an agent reads ten files in a row, those twenty messages stay in context long after they've been processed. This middleware quietly collapses them into a single line, keeping only the most recent result. The expensive stuff (LLM summarization) triggers less often.

No LLM calls. No hallucination risk. Stateless.

Quick Install

pip install langchain-collapse

🤔 What is this?

Agents burn through context by accumulating tool results they've already processed. A typical file exploration phase (8 reads, 4 greps) can eat thousands of tokens that just sit there. CollapseMiddleware scans for these repetitive groups and replaces the older ones with a short note, keeping the last result visible to the model.

On a realistic coding session, this produces a 92% token reduction. When paired with SummarizationMiddleware, summarization triggers 4.2x later because context fills up more slowly.

from langchain.agents import create_agent
from langchain_collapse import CollapseMiddleware

agent = create_agent(
    model="anthropic:claude-sonnet-4-6",
    tools=[...],
    middleware=[CollapseMiddleware()],
)

With SummarizationMiddleware

Place CollapseMiddleware first. It reduces the message count before summarization decides whether to fire:

from langchain.agents.middleware import SummarizationMiddleware

middleware = [
    CollapseMiddleware(),
    SummarizationMiddleware(
        model="anthropic:claude-haiku-4-5-20251001",
        trigger=("fraction", 0.85),
    ),
]

Configuration

CollapseMiddleware(
    collapse_tools=frozenset({"read_file", "grep", "glob", "web_search"}),  # default
    min_group_size=2,  # minimum consecutive pairs to collapse
)

📖 Documentation

• Source (single file, ~150 lines)
• Benchmark (realistic session with token counts)
• Tests (unit tests + property-based invariant tests)

💁 Contributing

git clone https://github.com/johanity/langchain-collapse.git
cd langchain-collapse
pip install -e ".[test]"
pytest

📕 License

MIT