Klaviyo's native flow library is genuinely good, and this article is not a teardown. Welcome series, abandoned cart, browse abandonment, post purchase: these are table stakes done well, and every Shopify brand should have them running. The limitation is structural, not a quality gap. Native flows are triggered by what customers do. They have no trigger for what the inventory does.
The Blind Spot, Concretely
Klaviyo does not know a SKU has been sitting for 90 days bleeding storage cost. It does not know the bestseller is down to two days of stock at current velocity. It does not know a product is selling at triple its baseline this week. All of that intelligence lives in Shopify's inventory and order data, and none of it arrives in Klaviyo on its own. The one native exception, the back in stock flow, depends on customers clicking a notify button, which captures a fraction of the buyers whose browse and cart behavior already proved intent.
The Extension, Not the Replacement
The inventory triggered engine does not replace Klaviyo, it feeds it. An automation layer watches Shopify's inventory webhooks and order velocity, applies the business rules (overstock thresholds, low stock thresholds, trend ratios, margin limits), and pushes custom events into Klaviyo with the product and offer data attached. Klaviyo still owns segmentation, templates, deliverability, and attribution, the things it is best at. The engine simply gives it a set of triggers it was never built to generate: the warehouse's side of the conversation.
The native versus extended comparison, flow by flow, is part of our inventory driven marketing engine page, including the exact custom events the engine pushes and what each one carries.