AWS c8i.4xlargevsAWS c8i-flex.4xlarge

c8i.4xlarge pairs 16 vCPUs with 32GB of RAM at $0.7497/hr On-Demand (about $540/mo at 24×7). c8i-flex.4xlarge pairs 16 vCPUs with 32GB at $0.7122/hr (~$513/mo). c8i-flex.4xlarge is 5% cheaper per hour than c8i.4xlarge ($0.0375/hr gap).

c8i.4xlarge (compute-optimized, Intel Xeon (x86_64)) and c8i-flex.4xlarge (compute-optimized, Intel Xeon (x86_64)) target different workload shapes. The vCPU:RAM ratios are different (16:32 vs 16:32), and depending on the architectures involved you may also see meaningful single-thread performance and per-hour-cost differences. This kind of cross-category comparison is most useful when you're early in the design phase and not yet sure whether your workload is CPU-bound, memory-bound, or balanced — once that's clear, the right pick is usually obvious.

On raw price-per-performance, the two are c8i-flex.4xlarge delivers ~5% more single-thread Sysbench score per dollar (4439 vs 4679 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 (28005 vs 28164) are what to weigh. Spot pricing flips many of these comparisons — when c8i.4xlarge drops to $0.2247/hr and c8i-flex.4xlarge drops to $0.3181/hr, the cheap-per-hour winner can swing meaningfully.

In practice, pick c8i.4xlarge when your workload is closer to compute-optimized (CPU-bound work — batch processing, web servers under sustained load, game servers). Pick c8i-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.