# LLM.txt - Claude Prompt Caching: When Five Minutes Beats One Hour ## Article Metadata - **Title**: Claude Prompt Caching: When Five Minutes Beats One Hour - **URL**: https://www.llmrumors.com/news/claude-prompt-caching-cost-break-even - **Publication Date**: September 20, 2026 - **Reading Time**: 10 min read - **Tags**: Claude, Anthropic, Prompt Caching, AI Pricing, API Economics, AI Agents, Developer Tools, Cost Optimization - **Slug**: claude-prompt-caching-cost-break-even ## Summary Calculate Claude prompt caching's break-even point, choose a TTL from actual reuse, and diagnose misses without confusing API savings with subscription limits. ## Key Topics - Claude - Anthropic - Prompt Caching - AI Pricing - API Economics - AI Agents - Developer Tools - Cost Optimization ## Content Structure This article from LLM Rumors covers: - Technical implementation details - Financial analysis and cost breakdown - Comprehensive source documentation and references ## Full Content Preview TL;DR: Claude cache writes cost 1.25 times base input for five minutes or 2 times for one hour; reads cost 0.1 times on Sonnet 4.6 and 0.025 on Fable 5.1.[1] In the Sonnet example below, five-minute caching becomes cheaper than uncached input on the second use, while one-hour caching needs a third use. These are calculated prefix costs, not measured application savings. The real story isn't the discount on a cache hit. It is whether your application buys enough hits to repay the writes. A long prompt that changes before every request can turn an optimization into a surcharge. Our Claude rivalry analysis explained why caching changes model economics. This guide takes the next step: calculate the purchase decision, choose a lifetime and inspect the bill. It uses Anthropic's documentation checked on September 20, 2026, not a claimed performance test. A cache is an investment in future reuse. Budget its first write, likely expiration and changing context before treating the advertised read price as your average input price. Cover: generated editorial artwork using reusable printing plates as a metaphor. It does not depict Anthropic infrastructure or measured savings. Price: Name the Model and Billing Route Our worked example uses Claude Sonnet 4.6 on the direct Claude API, standard synchronous processing, global routing, and published USD rates. It excludes negotiated discounts, batch pricing, geographic premiums and paid tool charges.[1] Anthropic still lists Sonnet 4.6 as an available legacy model with the API ID claude-sonnet-4-6. This is an accounting example, not a recommendation to choose it over newer models.[9] | Billing category | Published Sonnet 4.6 price per million tokens | | --- | ---: | | Uncached input | $3.00 | | Five-minute cache write | $3.75 | | One-hour cache write | $6.00 | | Cache read | $0.30 | | Output | $15.00 | Source: Anthropic pricing, checked September 20, 2026. These are vendor prices, not a cross-model performance comparison. A write is its own billing category. Do not charge the same written token once at $3 and again at $3.75. Conversely, a cheap prefix read does not make fresh input or generated output cheap. Those remain separate costs. The Fable/Mythos 5.1 exception makes a universal 0.1 multiplier wrong.[1] Break-Even: Count Successful Reuses After the Write Assume an unchanged 6,000-token prefix, one initial write and successful reads thereafter. All requests use the same model and eligible cache, before expiration. The prefix costs $0.018 uncached, $0.0225 to write for five minutes, $0.036 to write for one hour, or $0.0018 to read. For n total requests, let B be the uncached prefix cost, w the write multiplier and r the read multiplier. The calculated cost is: ``text Uncached: n × B Cached: B × [w + (n − 1) × r] Caching is cheaper when n > (w − r) / (1 − r) ` | Total uses of the same prefix | No cache | Five-minute: one write | One-hour: one write | | --- | ---: | ---: | ---: | | 1 | $0.0180 | $0.0225 | $0.0360 | | 2 | $0.0360 | $0.0243 | $0.0378 | | 3 | $0.0540 | $0.0261 | $0.0396 | | 10 | $0.1800 | $0.0387 | $0.0522 | Hypothetical arithmetic using the published Sonnet 4.6 rates above. Each cached column assumes one write and all remaining uses are hits; no runtime measurements were performed. At ten uses, prefix-only savings are 78.5% for five minutes and 71% for one hour. But add 1,000 uncached input tokens and 500 output tokens to each request: those add $0.105 across ten requests. Whole-request totals become $0.285 uncached, $0.1437 with five-minute caching and $0.1572 with one-hour caching. The prefix discount is not the invoice discount. Sensitivity: The Price of Repeated Cold Starts Keep the ten-request, 6,000-token example, but allow full-prefix rewrites. The following are hypothetical billing outcomes with no partial hits. E... [Content continues - full article available at source URL] ## Citation Format **APA Style**: LLM Rumors. (2026). Claude Prompt Caching: When Five Minutes Beats One Hour. Retrieved from https://www.llmrumors.com/news/claude-prompt-caching-cost-break-even **Chicago Style**: LLM Rumors. "Claude Prompt Caching: When Five Minutes Beats One Hour." Accessed September 20, 2026. https://www.llmrumors.com/news/claude-prompt-caching-cost-break-even. ## Machine-Readable Tags #LLMRumors #AI #Technology #Claude #Anthropic #PromptCaching #AIPricing #APIEconomics #AIAgents #DeveloperTools #CostOptimization ## Content Analysis - **Word Count**: ~1,890 - **Article Type**: News Analysis - **Source Reliability**: High (Original Reporting) - **Technical Depth**: Medium - **Target Audience**: AI Professionals, Researchers, Industry Observers ## Related Context This article is part of LLM Rumors' coverage of AI industry developments, focusing on data practices, legal implications, and technological advances in large language models. --- Generated automatically for LLM consumption Last updated: 2026-09-20T14:09:03.413Z Source: LLM Rumors (https://www.llmrumors.com/news/claude-prompt-caching-cost-break-even)