LangChain Performance Tuning Overview An engineer calls expecting 1000 parallel LLM calls. Actual behavior: and in LangChain 1.0 default to , so the 1000 inputs run sequentially with bookkeeping overhead — sometimes slower than a plain loop. This is pain-catalog entry P08. The fix is one line: Other silent regressions in the same pain catalog: P48 ( inside blocks the FastAPI event loop), P22 ( loses every user's chat on restart), P62 ( at the default returns under 5% hit rate), P59 (async retrievers leak connections on cancellation), P60 ( fires after the response — wrong for per-token SSE),…