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An agent is repetitive by design. Every step of a run sends the same system instructions, the same tool schemas and the same growing conversation, then adds a little new material at the end. By the time a run finishes, most of the tokens the model has read were tokens it had already read on a previous step.

We treat that repetition as what it is: work the server has already done. Any part of your prompt that matches the start of a request we have recently served is billed as cached input, at one tenth of the normal input price. You do not have to switch anything on. It happens on every key, on every model.

What it means for your bill

Take a typical agent run: a long tool preamble, a dozen steps, a few thousand tokens of tool output per step. Most of what you send is repeated prefix. Billed at a tenth, that repeated part stops being the cost driver. Long, careful system prompts, big tool schemas and full conversation history become affordable, which is exactly what makes agents reliable.

Three habits that make it work

Put what is stable at the front. System instructions, tool definitions, the document you are working on. The cache matches from the first token forward, so everything before the first change is free-ish and everything after it is full price.

Put what changes at the end. The current question, the latest tool result, the timestamp. A single changing value at the top of your prompt, like a date in the first line of your system message, throws away the whole benefit.

Keep the order stable across steps. If your framework reorders messages or rewrites the system prompt between calls, the prefix no longer matches. Most agent frameworks get this right by default; it is worth checking once.

See it on the dashboard

Every key reports its cache hit rate next to tokens and spend. Change the order of your prompt and you will see the number move within a few requests. If it stays low and you think it should not, write to us with the key name and we will look at the traffic pattern with you.

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