Tech Ocean

Apr 25, 2026 · Artificial Intelligence

LangGraph Day 2: Watching State Changes Like a TV Series with State + Reducer

This article explains LangGraph’s two state‑update modes—overwrite and merge—shows how to use Annotated with custom reducers such as operator.add or add_messages, demonstrates when reducers run, and provides full Python examples, including persistence with checkpointers and custom merge functions.