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Stack of glass blocks, the lower ones cached
Every time you send a message, the AI re-reads everything before it: instructions, tool definitions and the whole conversation — usually 90%+ of the input. Prompt caching lets the provider keep that already-processed beginning in memory, so the next message only pays full price for what is new.

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The economics

Current list prices per million tokens: Cached tokens also skip most of the compute, so the first word of the answer arrives sooner.

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Why most apps get this wrong

A cache only works if the beginning of the prompt is byte-for-byte identical to last time. Many chat apps break it on every message:
  • They slide the history window by one message per turn, so the start changes every time.
  • They insert timestamps, search results or memory near the top.
  • They spread a conversation across servers, each with a cold cache.
  • They mark one cache point, or mark it inside text that later changes.

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How Aura does it

1

Stable layout

Unchanging content (instructions, tools) always goes first. Anything that changes each turn — live search results, files, the time — goes at the end.
2

Two cache points, placed carefully

The system prompt gets a one-hour cache and a second point lands on the last settled message — never inside the newest four messages, which can still change.
3

History moves in blocks of 10

Aura keeps a rolling 40-turn history but drops old messages ten at a time, so the cached beginning stays valid for many turns in a row.
4

Sticky routing

Every conversation carries a stable session key, so it keeps landing on the same warm cache instead of a cold server.
5

Per-model handling

Claude, Gemini and GPT cache differently (explicit breakpoints, last-breakpoint-only, or cache keys). Aura applies the right method to each.
Speedometer and coin jar

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Measured results

  • In a recent 7-day sample of logged requests, 69% of all input tokens were served from cache.
  • A repeated 17,000-token chat turn dropped from 0.0347to0.0347 to 0.0018 — about 95% cheaper.
  • A repeated 26,000-token AI Builder scan dropped from 0.21to0.21 to 0.009.
Those savings are why Aura can offer Unlimited chat and low per-message credits.

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Keep your cache warm

  • Stay in one chat per topic. A new chat starts cold.
  • Follow up quickly — conversation caches last about 5 minutes; instruction caches about an hour.
  • Attach files once, early, instead of re-uploading them.
Only briefly, in the provider’s memory, scoped to your conversation, and it expires automatically. It is never used for training and is compatible with Zero Data Retention.
No. A cache only matches an identical prompt beginning, which includes your private conversation.