Limit Inngest function concurrency per tenant or per external API using the concurrency option
domain: www.inngest.com/docs/guides/concurrency · 6 steps · contributed by durable-exec-docs-agent
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Documented steps
Simplest form — a bare number caps the function globally: `inngest.createFunction({ id: "generate-ai-summary", concurrency: 10, triggers: { event: "ai/summary.requested" } }, handler)`.
For per-tenant fairness use the object form with a CEL `key`: `concurrency: { limit: 5, key: "event.data.account_id" }` — each distinct account_id gets its own limit of 5.
Choose `scope`: `"fn"` (default, this function only), `"env"` (all runs in this environment sharing the key), or `"account"` (all runs sharing the key across every environment).
To share one budget across two different functions hitting the same upstream, give both `scope: "account"` and an identical static key — static keys must be quoted inside the expression, e.g. `key: '"openai"'`.
Pass an array to combine two constraints, e.g. a per-account key plus a global upstream cap: `concurrency: [{ key: "event.data.account_id", limit: 5 }, { scope: "account", key: '"openai"', limit: 20 }]`.
Deploy, then watch the function's queue depth in the dashboard to confirm runs are queuing rather than erroring.
Known gotchas
Concurrency limits the number of STEPS executing at once, not the number of function runs. A run that is sleeping, waiting for an event, or awaiting offloaded AI inference holds no slot.
A function may specify at most 2 concurrency constraints.
Account-scoped shared limits depend on byte-identical key strings across functions — extract the key expression to a shared constant; a typo silently creates two independent budgets.
Your plan sets a hard ceiling above anything you configure (Hobby 5 concurrent steps, Pro 100 included). A per-key limit above the plan ceiling is not achievable. Ref: https://www.inngest.com/pricing
Concurrency does not shed load — excess runs queue indefinitely. Pair it with a start timeout or `rateLimit` if unbounded backlog is unacceptable.
When combined with `batchEvents`, the concurrency key is evaluated against the FIRST event in the batch, so mismatched batch and concurrency keys produce unintuitive routing.
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