LangChain's LCEL Replaces Legacy Chains With Modular, Pipe-Based Pipelines

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LangChain's LangChain Expression Language (LCEL) is now the recommended standard for building AI workflows, replacing the older class-based Legacy Chains approach. Legacy Chains required developers to memorize specific class names, match variable names precisely, and rewrite entire classes when adding new functionality. LCEL instead uses a pipe operator (|) to define a clear, visual sequence of components, where each step passes its output directly to the next. The new approach offers built-in streaming, a standardized interface with consistent methods like .invoke() and .stream(), and easy composability that lets developers insert or swap components without breaking the pipeline. Developers are advised to use LCEL for all new projects, while keeping chains concise to avoid debugging complexity.

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