Email marketing is the highest-ROI channel for most e-commerce stores. So when both Klaviyo and Sendlane started shipping AI features, we ignored the press releases and ran a real test instead.
Over 90 days, we used a 22,000-contact Shopify store generating roughly $180k/year to run identical campaigns through both platforms. Same audience. Same products. Same sending windows. Different AI capabilities.
The headline result: Klaviyo wins on raw performance. Sendlane wins on cost-per-revenue-dollar. The right answer depends on your store size.
The setup
We split the email list 50/50 by random assignment. For 90 days, identical campaigns were sent through both platforms using native AI features. Total revenue attributed: $53,200 through Klaviyo, $48,900 through Sendlane.
Subject line AI
Sendlane’s AI subject line testing automatically rotates winners across campaigns — produced 12.3% open rate improvement. Klaviyo’s lift was smaller at 8.1%, but more predictive.
Product recommendation blocks
Klaviyo’s recommendation engine produced 3.4x higher click-through on recommended products. For abandoned cart flows, Klaviyo recovered an additional 4.1% of revenue.
The cost equation
Klaviyo: $590/month → $53,200 revenue = $44.27 per dollar spent. Sendlane: $349/month → $48,900 revenue = $46.71 per dollar spent. Sendlane is better value for stores under $250k/year.
What we recommend
Under $250k/year: Sendlane. Above $250k/year: Klaviyo.