LangChain SDK Patterns (Python)

Overview

chain.batch(inputs) in LangChain 1.0 does not parallelize by default. The max_concurrency parameter defaults to 1 in several provider packages (notably older langchain-openai), so a call like chain.batch(inputs_1000) runs 1,000 sequential round-trips — same wall-clock time as a for loop, plus the overhead of the batch machinery. Users file "batch is slow" tickets, benchmark it against asyncio, and move to a different framework — when the fix is two lines:

# BAD — silently serializes (P08)
chain.batch(inputs_1000)

# GOOD — 10 in flight at once
chain.batch(inputs_1000, config={"max_concurrency": 10})