# Prompt Caching

> Reusing the model's processed state for a repeated prompt prefix so identical leading context is not recomputed, cutting latency and cost.

_The Agentic Web Lexicon · /glossary/prompt-caching · [JSON](/api/glossary/prompt-caching) · [all The Agentic Web Lexicon](/glossary)_

- **term:** Prompt Caching
- **category:** knowledge-memory
- **short_def:** Reusing the model's processed state for a repeated prompt prefix so identical leading context is not recomputed, cutting latency and cost.
- **long_def:** Introduced by Anthropic on 14 August 2024, prompt caching marks a content block as a cache breakpoint; a later request that begins with the same exact bytes reads the cached state instead of reprocessing it. Cached input typically costs a fraction of normal input tokens (with a one-time write surcharge). It rewards stable, front-loaded context — a direct incentive to put durable, machine-readable material first.
- **see_also:** token-economics, context-engineering, agent-skills
- **etymology_origin:** Introduced by Anthropic for the Claude API on 14 August 2024; caches a prompt prefix marked as a breakpoint, with an ephemeral (short-TTL) cache reused across subsequent requests.
- **related_to:** token-economics, context-engineering, agent-skills, agentic-loop
- **contrast_with:** Unlike RAG, which fetches new context per query, prompt caching reuses unchanged leading context across calls — it optimizes repeated identical input rather than retrieving fresh information.
- **example:** Anthropic launched prompt caching on 14 August 2024; cached tokens cost a fraction of normal input tokens, rewarding stable, repeated prompt prefixes.
- **source:** https://claude.com/blog/prompt-caching
- **status:** active
- **why_it_matters:** Prompt caching makes stable, front-loaded, machine-readable context cheaper to reuse across an agent's loop — another economic reason clean structure beats sprawling markup.
- **sameAs:** —
- **bridge_entity:** agent-readiness
- **last_verified:** 2026-06-15
- **md_twin:** /glossary/prompt-caching.md