--- title: The KV Cache: Build It, Break It, Measure It | daily.dev description: A deep dive into KV caching for autoregressive LLM inference, built from scratch on GPT-2. Covers the mathematical justification for why past keys and values... canonical: https://daily.dev/posts/the-kv-cache-build-it-break-it-measure-it-tfe16aucn twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: The KV Cache: Build It, Break It, Measure It | daily.dev og:description: A deep dive into KV caching for autoregressive LLM inference, built from scratch on GPT-2. Covers the mathematical justification for why past keys and values... og:url: https://daily.dev/posts/the-kv-cache-build-it-break-it-measure-it-tfe16aucn og:image: https://api.daily.dev/og/posts/tFE16AucN.png og:image:alt: The KV Cache: Build It, Break It, Measure It og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # The KV Cache: Build It, Break It, Measure It **[Medium](https://daily.dev/sources/medium_js)** · 20 min read · 0 upvotes · 0 comments ## Summary A deep dive into KV caching for autoregressive LLM inference, built from scratch on GPT-2. Covers the mathematical justification for why past keys and values never change under causal attention, a ~120-line implementation loading real pretrained weights, a formal correctness proof, and three common bugs (wrong position offsets, incorrect causal masking during decode, batching pitfalls). Benchmarks on a free Colab T4 show 1.4–3.2× wall-clock speedups depending on prompt length. The post also quantifies the memory cost per token for models from GPT-2 to Llama-3.1-70B, and explains why the naive torch.cat cache implementation copies gigabytes unnecessarily — motivating preallocated static caches and CUDA graph compatibility. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [KV Caching in LLMs: A Guide for Developers](https://daily.dev/posts/kv-caching-in-llms-a-guide-for-developers-hfpim4eo0) · Machine Learning Mastery · 1 upvotes · 0 comments - [How KV Caching Slashes LLM Inference Costs at Scale](https://daily.dev/posts/how-kv-caching-slashes-llm-inference-costs-at-scale-7g9k0lnod) · DigitalOcean Community · 0 upvotes · 0 comments - [Rethinking KV Caching For Production Inference](https://daily.dev/posts/rethinking-kv-caching-for-production-inference-1px3uv98r) · Daily Dose of Data Science \| Avi Chawla \| Substack · 0 upvotes · 0 comments --- Tags: [#nlp](https://daily.dev/tags/nlp), [#pytorch](https://daily.dev/tags/pytorch), [#ai-inference](https://daily.dev/tags/ai-inference) [View this post on daily.dev](https://daily.dev/posts/the-kv-cache-build-it-break-it-measure-it-tfe16aucn) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"The KV Cache: Build It, Break It, Measure It","url":"https://daily.dev/posts/the-kv-cache-build-it-break-it-measure-it-tfe16aucn","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/the-kv-cache-build-it-break-it-measure-it-tfe16aucn"},"datePublished":"2026-07-24T05:40:56.739Z","dateModified":"2026-07-24T05:42:31.499Z","description":"A deep dive into KV caching for autoregressive LLM inference, built from scratch on GPT-2. Covers the mathematical justification for why past keys and values...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/17e695180133a9395008a92d2090c9d3?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/17e695180133a9395008a92d2090c9d3?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Medium","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Medium","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/medium","url":"https://daily.dev/sources/medium_js"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/the-kv-cache-build-it-break-it-measure-it-tfe16aucn","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"nlp,pytorch,ai-inference","timeRequired":"PT20M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Medium","item":"https://daily.dev/sources/medium_js"},{"@type":"ListItem","position":3,"name":"The KV Cache: Build It, Break It, Measure It"}]} ```