# runnable

> **Module** in `langchain_classic`

📖 [View in docs](https://reference.langchain.com/python/langchain-classic/schema/runnable)

LangChain **Runnable** and the **LangChain Expression Language (LCEL)**.

The LangChain Expression Language (LCEL) offers a declarative method to build
production-grade programs that harness the power of LLMs.

Programs created using LCEL and LangChain Runnables inherently support
synchronous, asynchronous, batch, and streaming operations.

Support for **async** allows servers hosting LCEL based programs to scale better
for higher concurrent loads.

**Streaming** of intermediate outputs as they're being generated allows for
creating more responsive UX.

This module contains schema and implementation of LangChain Runnables primitives.

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[View source on GitHub](https://github.com/langchain-ai/langchain/blob/79cab2dc7f58be720cac43db3677b4c1fd971f91/libs/langchain/langchain_classic/schema/runnable/__init__.py)