Karpenter vs Cluster Autoscaler: Which to Use in 2026

Karpenter is an open-source node provisioner that offers a direct API request approach for provisioning cloud instances, optimizing instance selection at scheduling time, and allowing for faster node readiness and greater instance flexibility compared to the Cluster Autoscaler (CAS), which operates within pre-defined node groups and typically takes longer to provision nodes. In 2026, Karpenter is the preferred choice for AWS and Azure due to its efficient node consolidation and native support for Spot instances with automatic fallback, while CAS remains the only viable option for GKE users as no official Karpenter provider exists for GCP. While Karpenter can consolidate workloads onto fewer nodes effectively, neither Karpenter nor CAS address pod-level overprovisioning, which is significant for optimizing overall costs. The addition of Cast AI's optimization stack, which includes pod-level rightsizing, can significantly enhance cost savings when used alongside Karpenter. Running both Karpenter and CAS simultaneously is possible but requires careful partitioning to avoid conflicts during migration.

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