AWS c8i-flex.4xlargevsAWS c8ib.4xlarge

c8i-flex.4xlarge pairs 16 vCPUs with 32GB of RAM at $0.7122/hr On-Demand (about $513/mo at 24×7). c8ib.4xlarge pairs 16 vCPUs with 32GB at $1.0886/hr (~$784/mo). c8i-flex.4xlarge is 53% cheaper per hour than c8ib.4xlarge ($0.3765/hr gap).

Both are generation-8 compute-optimized instances, but they run on different silicon: **c8i-flex.4xlarge** is Intel Xeon (x86_64), **c8ib.4xlarge** is Intel Xeon (x86_64). AMD variants (suffix `a`) are typically 10% cheaper than Intel siblings at comparable single-thread performance. Graviton variants (suffix `g`) are usually 20–40% cheaper but require ARM64-compatible binaries — most modern Linux stacks are fine, but verify any compiled extensions, native modules, or third-party binaries before migrating. Same vCPU/RAM ratio, same network performance class, different processor.

On raw price-per-performance, the two are c8i-flex.4xlarge delivers ~52% more single-thread Sysbench score per dollar (4679 vs 3086 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 (28164 vs 28255) are what to weigh. Spot pricing flips many of these comparisons — when c8i-flex.4xlarge drops to $0.3181/hr and c8ib.4xlarge drops to $0.5309/hr, the cheap-per-hour winner can swing meaningfully.

In practice, pick c8i-flex.4xlarge when your workload is closer to compute-optimized (CPU-bound work — batch processing, web servers under sustained load, game servers). Pick c8ib.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.