Why AI Can’t Be Both Instant and Cheap: Latency vs Throughput

Business Pill 14 · Latency versus throughput

There are two ways for an AI system to be fast, and they pull against each other. That trade-off is called latency versus throughput.

A short explainer video. The numbers in it are round numbers for illustration.

Two Ways to Be Fast

There are two ways for an AI system to be fast. The first is latency: how long one person waits for an answer. The second is throughput: how many answers the system produces in total every second.

Think of a sports car and a bus. The car leaves the moment you sit down, but it carries one person. The bus carries many, but it waits until it is full.

Batching

AI chips work the same way. They can answer one request at a time, immediately. Or they can collect many requests and process them together. That is called batching.

With batching, the chip does far more work in total, but each request waits a little longer.

A Worked Example

The video uses round numbers. One at a time, a chip gives one answer every second. In a batch of eight, it takes two seconds but delivers eight answers. That is four answers per second, four times the output from the same chip.

So each answer costs a quarter as much, but everyone waited twice as long. This is the trade-off: you can make AI faster for each person, or cheaper for everyone. Pushing one costs you the other.

Bar chart: one answer per second one at a time and four answers per second in a batch of eight
Four times the output from the same chip, at the cost of each request waiting twice as long. Round numbers for illustration.

Why the Same Model Has Different Prices

The trade-off explains why the same model is sold at different prices. A live conversation needs its answer now, so it pays the premium. A report that runs overnight can wait in the queue, so it gets the discount.

And as more work is handed to agents running in the background, more of it can wait. More of it takes the bus.

Three Questions to Ask

  1. Who is waiting for this answer?
  2. How long can they wait?
  3. What is that patience worth?

See It in the News

OpenAI Prices Astra Ultrafast at 6x Standard. A news piece reading a published price ladder in which speed is the priced variable.

How This Concept Connects

Layer 3 of 8 · Inference & Context, on the Business Engineer Concept Map

InferencePercentilesRate LimitsWhy AI Canโ€™t Be Both Instant and Cheap
  • Why AI Canโ€™t Be Both Instant and Cheap builds on Inference. Batching lets a chip serve many requests together at the cost of each waiting longer, a choice in how inference is served.
  • Why AI Canโ€™t Be Both Instant and Cheap builds on Percentiles. Latency is how long one person waits, and percentiles show the slow end of those waits that an average hides.
  • Rate Limits (lesson unlocks soon) contrasts with Why AI Canโ€™t Be Both Instant and Cheap. Both are about busy capacity: rate limits cap requests per minute, batching trades each user’s wait for more answers overall.
Business Engineer framework
The State of the Inference Economy
Serving trade-offs set inference prices.
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