LangChain Deep Agents (Python)

Overview

Two pains bite every team reproducing LangChain's late-2025 Deep Agents blueprint.

Virtual-FS state grows unboundedly (P51). The planner and every subagent write plans, scratch notes, intermediate drafts, and tool outputs into state["files"]. Nothing ever evicts them. After 50 tool calls, the checkpointed state is 8 MB; every MemorySaver.put() takes 400 ms; a run that started at 1.2 s per node visit ends at 2.5 s per node visit. The LangSmith trace viewer times out loading the thread. The user sees latency doubling over the run with no obvious tool-level culprit.