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OpenLast checked LangGraph#state

Command update on a new thread applies the update twice

Invoking a graph with Command(update=...) when the thread has no prior checkpoint applies the update twice. With an operator.add channel the report printed ['cmd', 'cmd', 'node'] instead of ['cmd', 'node'].

From GitHub

langchain-ai/langgraph

Issue

Difficulty
Easy
Time
~5 min
Steps
2
Fixed in
—
Last checked

Not fixed upstream yet: the issue is open. Source: issue open. Last checked 2026-10-23.

Symptom

Invoking a graph with Command(update=...) when the thread has no prior checkpoint applies the update twice. With an operator.add channel the report printed ['cmd', 'cmd', 'node'] instead of ['cmd', 'node'].

Evidence what you'll see

  • On langgraph 1.2.16 the snippet printed no checkpointer: ['cmd', 'cmd', 'node'] and the same doubled list for InMemorySaver durability sync, async, and exit.
  • plain dict input: printed ['cmd', 'node'].
  • The same doubled result appeared on main at 9e6fc45c. A comment reproduced it on main 98043c37.

Why it happens

On a fresh run, _first() applies the Command as null-task writes, then passes the same Command to the START input task, which applies the update again. Pull request 9322 repaired the resumed-thread case. This is the first-run version.

Affected versions

langgraph 1.2.16, langgraph-checkpoint 4.3.0, Python 3.12.9. Also seen on main 9e6fc45c and 98043c37. Follow-up to issue #9322.

Fix steps

0 of 2 done

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How to check it worked

  • The report's snippet prints ['cmd', 'node'] for Command(update={"plain": ["cmd"]}) with no checkpointer and with InMemorySaver, matching the plain dict input.

If it still fails

  • A comment notes that a restricted input_schema can still need the early-write path so fields outside that schema stay writable, and that a direct Pregel workflow may have no START extractor.
  • The linked issue does not name a release that applies a fresh Command(update=...) once.

Sources and credit

Summarized in our own words from these public reports. Credit goes to their authors.

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