Streaming vs batch mode cost comparison
A common misconception is that streaming a response costs more in tokens. It does not — the token price is identical. What differs is infrastructure: streaming holds a connection open for the entire response, so at scale you must provision enough capacity to hold every in-flight stream at once. This tool models that difference so you can decide where streaming is worth the server bill.
How it works: Little’s Law
The core insight is Little’s Law: the number of concurrent items in a system equals the arrival rate multiplied by the average time each item spends in the system. Applied to streaming:
concurrent connections = requests per second × average response time (seconds)
For example, 10 requests per second at an average response time of 8 seconds requires 80 concurrent connections held open at any moment. If one server can hold 20 simultaneous streams, you need at least 4 servers running full-time just to carry that load.
Batch processing decouples arrival from processing: requests go into a queue and a smaller worker fleet drains it at its own pace. You size for throughput (how many requests per hour the workers must complete) rather than peak concurrency, which typically requires far fewer always-on servers.
The tool computes:
servers (streaming) = concurrent_connections / streams_per_server
monthly cost = servers × hourly_cost × 730
servers (batch) = model of throughput-sized workers, a fraction of streaming fleet
Worked example
Traffic: 5 requests per second. Average response: 10 seconds. Server: holds 25 streams, costs £0.15/hour.
Streaming:
- Concurrent connections = 5 × 10 = 50
- Servers needed = 50 / 25 = 2 servers
- Monthly = 2 × £0.15 × 730 = £219/month
Batch (illustrative):
- Queue workers sized for throughput, not concurrency
- Rough estimate: 1–2 workers handling the same volume asynchronously
- Monthly = roughly £55–110/month
These are illustrative figures. Enter your own RPS, response time, and server capacity for a real comparison.
When streaming is worth the premium
Streaming is worth the higher infrastructure cost when users are waiting for the response in real time. The first-token latency of a streamed response — the time until the user sees the first word — is dramatically lower than waiting for a complete batch response. For chat interfaces, writing assistants, and interactive tools, that perceived speed is the product quality.
For backend pipelines — data extraction, summarisation, classification, report generation that runs overnight — batch is almost always cheaper and operationally simpler. Requests arrive, queue, process, and the result is written to storage. No persistent connections, no connection-count ceiling, and you can process across off-peak hours to use cheaper spot or preemptible compute.
Planning estimate caveats
The model uses a simplified concurrency calculation. Production systems add autoscaling (which changes cost dynamics), load balancers (small fixed overhead), and retry budgets (which increase effective RPS). Treat the monthly figures as a directional comparison, not a procurement quote.