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Usable here means routable for workloads. AWS and Azure each reserve first 4 + last 1; GCP reserves first 2 + last 2; OCI reserves first 2 + last 1. IPv6 subnets are /64 almost everywhere — the host count is meaningless at that size (~18 quintillion), so the panel shows the prefix you get and the reservations that still apply. Built on the cross-cloud Networking Matrix.