Anthropic 409 conflict_error: the resource changed under you, resolve then retry

TL;DR: A 409 means your request conflicts with the current state of a resource: concurrent modification or a uniqueness violation. Not for different error messages. 409 conflict_error: re-read state, then decide Two writers touched the same resource, or you tried to create something that must be unique and it already exists. If the conflict is a uniqueness violation (a value that must be unique is already in use), stop: retrying the identical create will 409 forever.

The fix

TL;DR: A 409 means your request conflicts with the current state of a resource: concurrent modification or a uniqueness violation. 409 conflict_error: re-read state, then decide Two writers touched the same resource, or you tried to create something that must be unique and it already exists. If the conflict is a uniqueness violation (a value that must be unique is already in use), stop: retrying the identical create will 409 forever.

The fix

1. Re-fetch the resource. Your copy of its state is stale; the fresh read is the truth.
2. If the conflict is a uniqueness violation (a value that must be unique is already in use), stop: retrying the identical create will 409 forever. Either reuse the existing resource or change the unique value.
3. If the conflict is a concurrent modification, apply your change on top of the fresh state and retry once.
4. Retry policy: exactly one careful retry after re-reading state. A 409 in a tight retry loop is how you turn a transient conflict into sustained load.
5. Make creates idempotent where the API supports it, so a retried create converges instead of conflicting.
6. Log both your attempted state and the fetched state when a 409 fires. That pair is the whole diagnosis.

When to use this

• You are seeing this exact error message; match the block above, not just part of it.
• The failing call matches the scenario in the title: Anthropic 409 conflict_error.
• You want the fastest verified fix before digging through logs.

When not to use this

• Your error text differs from the block above; close cousins often have different causes.
• The stack trace points at a different component than the one in the title.
• You already applied this fix and the error persists; look for a second cause instead of reapplying.

Compatibility

• Not pinned to a specific version; follows current Anthropic behavior.

Anthropic's error reference: conflict_error means the request conflicts with the current state of a resource, e.g. concurrent modification or a non-unique value; resolve the conflict, then retry. Verified live at https://platform.claude.com/docs/en/api/errors.