CPU-Hour vs Wall-Clock Pricing for Sandboxes: Which One Costs Less?

Sandbox pricing differs between active CPU-hour models, which charge only when code uses CPU, and wall-clock models, which charge for the full time a sandbox remains running regardless of activity; this distinction is particularly significant for AI agents that spend much of their time waiting for models, APIs, or users. Upstash Box pay-as-you-go, Vercel Sandbox, and Cloudflare Sandbox bill active CPU, while E2B, Daytona, Modal, and Upstash Box keep-alive generally use wall-clock billing, with memory frequently charged by elapsed time even under active-CPU plans. For a 2 vCPU, 4 GB sandbox used intermittently for 10 core-minutes in an hour, Upstash Box pay-as-you-go costs about $0.017 compared with roughly $0.166 on E2B, though sustained workloads can favor lower wall-clock rates. In the example, Box pay-as-you-go remains cheaper than E2B or Daytona until average CPU use reaches about 83%, whereas Vercel’s wall-clock memory charges cause it to break even with E2B at about 32% CPU utilization. CPU-based billing is therefore best suited to bursty agents and tasks with long waits, while wall-clock plans may be preferable for continuously busy builds, tests, and data jobs, and always-on applications require separate consideration of idle behavior and availability. Upstash Box offers both active-CPU pay-as-you-go and fixed-price keep-alive options, with the latter costing $8 monthly for a small 2 vCPU box and becoming cheaper than pay-as-you-go when average usage exceeds roughly 5.5% over a full month.

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