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What AI costs

Why is my AI bill this high and how do I cut it?

Short answer

Most of an AI bill is the context you send, not the answers you get back — the input side is roughly 90% of the cost. The fix is sending less: a narrower working folder, fresher sessions, and caching the parts you reuse.

There are two different bills hiding behind “what does AI cost.” One is the seat someone pays for each month — a purchasing decision made once, then forgotten. The other is usage-based spend, which moves every day depending on how people actually work. It’s the second one that produces the meeting where a number went up and nobody changed anything.

The surprise is always in the same place, and it’s the opposite of where people look. The expensive part isn’t the model thinking, and it isn’t the long answers it writes back. It’s everything you send in — the files, the history, the standing instructions riding along on every single request. Which means the cost question and the context question are the same question wearing different clothes: a tight, deliberate context is both cheaper and better. You rarely have to trade one for the other.

That framing also explains why prompt caching matters more than its name suggests. If you’re going to send the same long instructions or the same big document turn after turn, the expensive work of reading it can happen once and be reused at a fraction of the price. It’s defined below, and it’s most of the reason a long working session doesn’t cost what a naive reading of the pricing page would predict.

Two habits do the bulk of the work, and neither needs a spreadsheet. Open the narrowest folder that actually contains the task, rather than pointing Claude at a shared drive and letting it wade. And start a fresh conversation when the subject changes, instead of letting one session carry an afternoon of unrelated history — see sessions for when to clear and when to keep going. When you want the real number rather than a feeling, /cost tells you what the current session has used.

One question that gets filed under cost but isn’t really: whether you need a more powerful computer. For almost every professional the answer is no — the model runs in a data centre and your laptop’s job is to display the result. The guide below covers the narrow cases where local hardware genuinely changes the answer, and why the current hardware market makes the cloud case stronger rather than weaker.

The words

Prompt caching Context caching
Prompt caching saves the model's processed version of text you send repeatedly — a long set of instructions, a big document — so it doesn't have to re-read it from scratch every turn. The next request reuses the cached part, which is much faster and far cheaper, since cached input is billed at a fraction of normal input. In a long Claude Code session, where the same context is reused turn after turn, it's one of the biggest cost savers there is.

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How to do it

  • /cost Show how many tokens this session has used, and the cost so far.