This article announces support for prefix delegation mode on Windows nodes in Amazon EKS, enabling higher pod density and reduced costs.

• Prefix delegation assigns /28 IPv4 prefixes (16 addresses) instead of individual secondary IPs
• Increases pod capacity from 14 to 224 pods on t3.2xlarge instances
• Supports up to 110 recommended pods per node, maximum 250 depending on instance type
• Available on Amazon EKS versions 1.25 and later with AWS Nitro instances
• Requires enabling in amazon-vpc-cni ConfigMap with enable-windows-prefix-delegation: "true"
• VPC Resource Controller manages IPv4 address allocation and warmpool management
• Configurable warm-ip-target, warm-prefix-target, and minimum-ip-target for scaling behavior
• Requires sufficient contiguous /28 CIDR blocks in subnets; Subnet CIDR Reservation recommended
• Create new node groups during migration from secondary IP mode to avoid inconsistencies

Prefix delegation significantly improves Windows container economics on Amazon EKS by enabling substantially higher pod density on individual nodes.