Klaviyo webhook outage: a six-hour pause your apps must survive
Klaviyo paused outbound event webhooks for six hours on October 22. Here is what happened and how to build webhook integrations that reconcile instead of break.
On Wednesday evening, Klaviyo paused outbound event webhooks for just over six hours. Nothing was lost. Klaviyo held the data and delivered the backlog overnight. But if your CRM sync, loyalty app, or Slack alert runs on Klaviyo webhooks, it went quiet without telling you. This Klaviyo webhook outage was short and handled well. It is still a good test: would your stack have noticed?
What actually happened
Per Klaviyo's status page, the incident ran like this (all times US Eastern):
- Oct 22, 5:11 PM: Klaviyo temporarily paused processing of new event webhooks. Customers and connected third-party apps saw delays.
- Oct 22, 11:28 PM: Processing resumed and new webhooks began to flow again while the backlog cleared.
- Oct 23, 2:40 AM: Klaviyo reported delivery fully restored. The incident was marked resolved that morning.
Two details matter. Klaviyo said webhook data was retained during the pause, so events arrived late, not never. And webhook actions inside flows were not affected. Only the event webhooks that push data out to other systems were delayed. Klaviyo did not publish a root cause on the status page.
Why webhook reliability matters for your business
Late is a different bug than missing. When a backlog drains, your endpoint gets hours of events in a burst, often out of order. If your handler assumes "newest arrives last," a 2:40 AM replay can overwrite fresher data with stale data. Compare event timestamps before you write.
Idempotency is not optional. Backlogs and retries can send the same event more than once. Key every write on the event ID. Double-counted loyalty points and duplicate CRM tasks are the usual symptoms.
Silence should page someone. Most teams alert on errors. A webhook pause produces no errors. It produces nothing. Track "last event received" per source and alert when it goes stale during business hours.
Reconcile on a schedule. Webhooks are the fast path, not the record. A nightly job that pulls recent profiles or events through Klaviyo's API and compares them to your copy catches anything a pause, a deploy, or a bad 500 dropped. We build every vendor integration this way, Klaviyo or not.
Key takeaways
- Klaviyo paused outbound event webhooks from 5:11 PM to 11:28 PM ET on October 22
- Data was retained and delivery was fully restored by 2:40 AM ET on October 23
- Flow webhook actions were not affected, only event webhooks to other systems
- Make handlers idempotent and order-aware, because backlogs replay in bursts
- Alert on silence and run a scheduled reconciliation against the vendor API
Not sure what happens when a vendor webhook goes quiet? We build integrations with idempotent handlers, staleness alerts and nightly reconciliation, so one vendor's bad night does not become your data problem. Ask us to review your integrations, or see how we build them.
Sources: Klaviyo Status: Outbound Webhook Delays, October 22-23, 2026.
- #klaviyo
- #webhooks
- #ecommerce
- #integrations
- #reliability
Tommy Rush — Founder, Rush Commerce
Operator turned builder. 15+ years running operations — now shipping the systems businesses run on. More
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