The 70% Problem: Fast Start, Hard Finish

Addy introduces the 70% problem where LLMs produce most of an app quickly but struggle with the final production-ready 30%.

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Brought to You By:

•⁠ Statsig ⁠ — ⁠ The unified platform for flags, analytics, experiments, and more.

•⁠ Linear – The system for modern product development.

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Addy Osmani is Head of Chrome Developer Experience at Google, where he leads teams focused on improving performance, tooling, and the overall developer experience for building on the web. If you’ve ever opened Chrome’s Developer Tools bar, you’ve definitely used features Addy has built. He’s also the author of several books, including his latest, Beyond Vibe Coding, which explores how AI is changing software development.

In this episode of The Pragmatic Engineer, I sit down with Addy to discuss how AI is reshaping software engineering workflows, the tradeoffs between speed and quality, and why understanding generated code remains critical. We dive into his article The 70% Problem, which explains why AI tools accelerate development but struggle with the final 30% of software quality—and why this last 30% is tackled easily by software engineers who understand how the system actually works.

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Timestamps

(00:00) Intro

(02:17) Vibe coding vs. AI-assisted engineering

(06:07) How Addy uses AI tools

(13:10) Addy’s learnings about applying AI for development

(18:47) Addy’s favorite tools

(22:15) The 70% Problem

(28:15) Tactics for efficient LLM usage

(32:58) How AI tools evolved

(34:29) The case for keeping expectations low and control high

(38:05) Autonomous agents and working with them