AWS c7i.8xlargevsAWS c7i-flex.4xlarge

c7i.8xlarge pairs 32 vCPUs with 64GB of RAM at $1.4280/hr On-Demand (about $1028/mo at 24×7). c7i-flex.4xlarge pairs 16 vCPUs with 32GB at $0.6783/hr (~$488/mo). c7i-flex.4xlarge is 52% cheaper per hour than c7i.8xlarge ($0.7497/hr gap).

Because both instances are in the **c7i 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: c7i.8xlarge gives you 32 vCPUs and 64GB of RAM, c7i-flex.4xlarge gives you 16 vCPUs and 32GB. 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 c7i-flex.4xlarge delivers ~107% more single-thread Sysbench score per dollar (2300 vs 4763 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 (53822 vs 27124) are what to weigh. Spot pricing flips many of these comparisons — when c7i.8xlarge drops to $0.6481/hr and c7i-flex.4xlarge drops to $0.2510/hr, the cheap-per-hour winner can swing meaningfully.

In practice, pick c7i.8xlarge when your workload is closer to compute-optimized (CPU-bound work — batch processing, web servers under sustained load, game servers). Pick c7i-flex.4xlarge 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.