Short answer: when you pass

create_if_missing=True

, the limit is created but not automatically enabled. So you end up with a “created, inactive” Global Concurrency Limit and your acquisition doesn’t actually gate anything. Delightful, I know. Workarounds you can use today: - Pre-create and enable the Global Concurrency Limit in the UI, then your

increment_concurrency_slots

calls will work as expected. - Docs: Global Concurrency Limits (Prefect 3) - Or, programmatically enable it immediately after creation by updating the limit to

active=True

via the Prefect client (same API you’re using to increment slots). If you share your Prefect version (2.x vs 3.x) I’ll give you a correct, version-specific snippet—the method names differ slightly. A couple quick checks: - In the UI, does the limit show up under Global Concurrency Limits with the Active toggle off? If yes, that’s exactly the behavior above. - Which Prefect version are you on, and are you using Cloud or Server? If you’d prefer not to touch the lower-level client at all, you can also gate work with Prefect’s concurrency context manager (async or sync), but even then you’ll want the limit pre-created and enabled for it to actually enforce the cap. Send me: - Your Prefect version - Cloud vs. Server - The code snippet you’re using to call

increment_concurrency_slots

I’ll respond with a drop-in snippet to auto-create-and-enable, and we’ll put this “inactive” phase behind us.