AWS c8i.8xlargevsAWS c8i-flex.12xlarge

c8i.8xlarge pairs 32 vCPUs with 64GB of RAM at $1.4994/hr On-Demand (about $1080/mo at 24×7). c8i-flex.12xlarge pairs 48 vCPUs with 96GB at $2.1365/hr (~$1538/mo). c8i.8xlarge is 42% cheaper per hour than c8i-flex.12xlarge ($0.6371/hr gap).

Because both instances are in the **c8i family**, the only thing that changes between them is sizing — same silicon, same architecture (Intel Xeon (x86_64)), same burstable/sustained behavior. The choice is purely about how much capacity you actually need: c8i.8xlarge gives you 32 vCPUs and 64GB of RAM, c8i-flex.12xlarge gives you 48 vCPUs and 96GB. AWS scales pricing close to linearly within a family, so picking the right size is mostly about right-sizing your workload, not getting a better deal per vCPU.

On raw price-per-performance, the two are c8i.8xlarge delivers ~43% more single-thread Sysbench score per dollar (2218 vs 1555 points per $1/hr). That's the cleanest signal we have for "which one runs your workload faster per dollar," but it only matters if your workload is single-thread-bound; for parallel workloads the multi-core scores (56026 vs 84021) are what to weigh. Spot pricing flips many of these comparisons — when c8i.8xlarge drops to $0.5733/hr and c8i-flex.12xlarge drops to $0.6794/hr, the cheap-per-hour winner can swing meaningfully.

In practice, pick c8i.8xlarge when your workload is closer to compute-optimized (CPU-bound work — batch processing, web servers under sustained load, game servers). Pick c8i-flex.12xlarge when it's closer to compute-optimized (CPU-bound work — batch processing, web servers under sustained load, game servers). When neither side is obviously right, the cheaper hourly rate usually wins for fault-tolerant batch workloads, while the higher single-core score usually wins for latency-sensitive web traffic. The regional pricing tables linked from each instance page below show where each is currently cheapest — sometimes a >20% regional gap flips the comparison entirely.