membrain-langchain

LangChain integration for Membrain — give your AI agents persistent, semantic long-term memory.

Membrain is a semantic memory system backed by PostgreSQL and pgvector. It stores memories as atomic notes, links related ones automatically via an LLM-powered Guardian, and supports graph-native retrieval — letting your agents recall facts, relationships, and context across sessions.

This package wires Membrain into LangChain with proper primitives: a BaseChatMessageHistory, a BaseRetriever, agent tools, and a high-level MembrainMemory class.

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Install

pip install membrain-langchain

# with OpenAI support
pip install "membrain-langchain[openai]"

# with uv
uv add membrain-langchain
uv add "membrain-langchain[openai]"

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Quick Start

Get a Membrain API key at mem-brain.io, then:

import asyncio
from membrain_langchain import MembrainClient, MembrainMemory
from langchain_openai import ChatOpenAI
from langchain_core.messages import SystemMessage, HumanMessage

client = MembrainClient(api_key="mb_live_...")
memory = MembrainMemory(client=client, user_id="user-123")
llm = ChatOpenAI(model="gpt-4o")

async def chat(user_message: str) -> str:
    # Fetch relevant memories and inject into the system prompt
    system_prompt = await memory.build_system_prompt(
        query=user_message,
        base_prompt="You are a helpful personal assistant.",
    )
    response = await llm.ainvoke([
        SystemMessage(content=system_prompt),
        HumanMessage(content=user_message),
    ])
    # Store the interaction for future recall
    await memory.store_interaction(user_message, response.content)
    return response.content

asyncio.run(chat("I love mani dum biryani"))
# Next message: the assistant already knows you love biryani

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What is Membrain?

Feature	Membrain	Typical vector store
Memory model	Atomic notes + semantic graph	Document/chunk store
Relationship search	Links are first-class searchable entities	No
Smart merge	Guardian auto-decides update vs create	Manual
Interpreted search	LLM summary of retrieved memories	No
Graph operations	Path-finding, hubs, neighborhood	No

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Classes

MembrainClient

The async HTTP client. All other classes use this internally.

from membrain_langchain import MembrainClient

client = MembrainClient(
    api_key="mb_live_...",
    base_url="https://mem-brain-api-cutover-v4-production.up.railway.app",  # default
    poll_interval=0.5,   # seconds between ingest job polls
    poll_timeout=30.0,   # max seconds to wait when wait=True
)

# Store a memory (waits for Guardian to complete linking)
result = await client.add_memory(
    content="User prefers dark roast coffee",
    scope=["user:user-123"],
    category="preference",
)

# Fire-and-forget (returns immediately after job is submitted)
await client.add_memory(content="...", wait=False)

# Semantic search
results = await client.search(query="coffee preferences", k=5, scope=["user:user-123"])

# Graph operations
await client.graph_neighborhood(memory_id="abc-123", hops=2)
await client.graph_hubs(limit=10)
await client.graph_path(from_id="abc", to_id="xyz")

# Stats
await client.get_stats()

---

MembrainMemory

High-level drop-in. Handles context retrieval and interaction storage automatically.

from membrain_langchain import MembrainMemory

memory = MembrainMemory(
    client=client,
    user_id="user-123",
    context_k=5,   # number of memories to inject per turn
)

# Get relevant memories as a formatted string
context = await memory.get_context("What coffee should I try?")

# Get a full system prompt with memory context appended
system_prompt = await memory.build_system_prompt(
    query="What coffee should I try?",
    base_prompt="You are a helpful assistant.",
)
# Returns: "You are a helpful assistant.\n\n## What you know about this user:\n- ..."

# Store a conversation turn (fire-and-forget)
await memory.store_interaction(user_msg="I love biryani", ai_msg="Noted!")

# Store an arbitrary fact (waits for confirmation)
await memory.add(content="User is vegetarian", category="dietary")

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MembrainRetriever

A proper BaseRetriever subclass. Plugs into any RAG chain.

from membrain_langchain import MembrainRetriever
from langchain_core.runnables import RunnablePassthrough
from langchain_core.output_parsers import StrOutputParser

retriever = MembrainRetriever(
    client=client,
    user_id="user-123",
    k=5,
    scope=None,           # defaults to ["user:{user_id}"]
    category=None,        # optional category filter
    include_related=True, # include linked neighbor memories
)

# Use in a RAG chain
chain = (
    {"context": retriever | format_docs, "question": RunnablePassthrough()}
    | prompt
    | llm
    | StrOutputParser()
)
answer = await chain.ainvoke("What does the user like to eat?")

Each result comes back as a Document with metadata:

Document(
    page_content="User loves mani dum biryani",
    metadata={
        "memory_id": "abc-123",
        "scope": ["user:user-123"],
        "semantic_score": 0.94,
        "related_memories": ["User is vegetarian"],
        "source": "membrain",
    }
)

Note: MembrainRetriever is async-only. Use chain.ainvoke() or await retriever.aget_relevant_documents(query).

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MembrainChatMessageHistory

A proper BaseChatMessageHistory subclass for use with RunnableWithMessageHistory. Persists conversation turns in Membrain scoped by user and session.

from membrain_langchain import MembrainChatMessageHistory
from langchain_core.runnables.history import RunnableWithMessageHistory

def get_history(session_id: str) -> MembrainChatMessageHistory:
    return MembrainChatMessageHistory(
        client=client,
        user_id="user-123",
        session_id=session_id,
        max_history=20,
    )

chain_with_history = RunnableWithMessageHistory(
    chain,
    get_history,
    input_messages_key="input",
    history_messages_key="history",
)

await chain_with_history.ainvoke(
    {"input": "What did I say earlier?"},
    config={"configurable": {"session_id": "session-abc"}},
)

Scope format: ["user:{user_id}", "session:{session_id}"]

• Search with scope=["user:user-123"] — all sessions for a user (long-term memory)
• Search with both scopes — isolated to one conversation

Note: Async-only. RunnableWithMessageHistory handles this automatically via ainvoke.

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get_membrain_tools()

Returns LangChain StructuredTool objects for use in ReAct / tool-calling agents.

from membrain_langchain import get_membrain_tools
from langgraph.prebuilt import create_react_agent
from langchain_openai import ChatOpenAI

tools = get_membrain_tools(
    client=client,
    user_id="user-123",
    include_graph_tools=False,  # set True to add neighborhood + hubs tools
)

agent = create_react_agent(ChatOpenAI(model="gpt-4o"), tools)
result = await agent.ainvoke({
    "messages": [{"role": "user", "content": "What do you remember about me?"}]
})

Available tools:

Tool	Description
membrain_search	Semantic memory search
membrain_add	Store a new memory
membrain_stats	Memory system statistics
membrain_neighborhood	Expand graph around a memory node (opt-in)
membrain_hubs	Most-connected memory nodes (opt-in)

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Patterns

Pattern A — MembrainMemory (automatic, always-on)

Retrieval and storage happen on every turn. The LLM receives memory as pre-injected context and never calls a tool.

User message → search Membrain → inject context → LLM → store interaction

Best for: simple chat apps, customer support bots, personal assistants.

Pattern B — Agent tools (LLM-driven)

The agent decides when to search, what to search for, and when to store new facts.

User message → Agent reasons → calls membrain_search → reasons → responds → optionally calls membrain_add

Best for: ReAct agents, research assistants, autonomous agents.

Pattern C — RAG pipeline

MembrainRetriever slots into a standard retrieval-augmented generation chain.

Question → retrieve relevant memories as Documents → LLM answers with context

Best for: knowledge-base Q&A, document assistants, domain-specific bots.

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Async-only

All Membrain API calls are async. This maps cleanly to modern LangChain (which uses ainvoke, astream, etc.) and FastAPI.

Sync stubs (messages property, add_message, clear, get_relevant_documents) raise NotImplementedError with a clear message pointing to the async equivalent.

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License

MIT

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Links

• Membrain
• Membrain Docs
• Get an API key
• LangChain Docs