m6g.16xlarge is AWS's general-purpose EC2 size at 64 vCPU and 256 GiB. In the name, "m" is the general-purpose line, "6" is the generation, "g" marks AWS Graviton (ARM) processors and "16xlarge" is the size within the m6g family. It runs on AWS Graviton2 Processor at 2.5 GHz, and AWS introduced it in May 2020. AWS has since shipped m7g, m8g and m9g; m7g.16xlarge is the direct replacement at this size, scoring 1,580,052 CoreMark/s against this instance's 1,277,445 — roughly 24% more throughput for the same vCPU count. The closest Spot shape is gp.vs2.2xlarge at 16 vCPU, so this instance maps to 4 of them — 64 vCPU and 256 GiB across the fleet, about 93% below the US East (N. Virginia) on-demand rate. Spot delivers compute as managed Kubernetes, so a node pool of that size is the native shape of the answer rather than a workaround — provided the workload scales horizontally.
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m6g.16xlarge gives you 64 vCPU and 256 GiB in a single machine. The largest comparable Spot node, gp.vs2.2xlarge, is 16 vCPU and 64 GiB, so the equivalent here is 4 nodes rather than one.
Spot runs as managed Kubernetes, so a 4-node pool is the normal way to run things rather than a workaround. If your workload already sits behind a load balancer, a queue or a scheduler, it spreads across them without changes. If it needs all 64 cores and 256 GiB in one process, it does not.
x86_64 onlym6g.16xlarge is Graviton (arm64) and Rackspace Spot has no arm64 nodes, so you'd be moving to x86. You'll need x86 builds of your images, and per-core speed differs between the chips — worth testing before you decide how many nodes to run.