What Codex is and how it works

Alexander Embiricos leads product on Codex, OpenAI’s powerful coding agent, which has grown 20x since August and now serves trillions of tokens weekly. Before joining OpenAI, Alexander spent five years building a pair programming product for engineers. He now works at the frontier of AI-led software development, building what he describes as a software engineering teammate—an AI agent designed to participate across the entire development lifecycle.

We discuss:

1. Why Codex has grown 20x since launch and what product decisions unlocked this growth

2. How OpenAI built the Sora Android app in just 18 days using Codex

3. Why the real bottleneck to AGI-level productivity isn’t model capability—it’s human typing speed

4. The vision of AI as a proactive teammate, not just a tool you prompt

5. The bottleneck shifting from building to reviewing AI-generated work

6. Why coding will be a core competency for every AI agent—because writing code is how agents use computers best

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Transcript: https://www.lennysnewsletter.com/p/why-humans-are-ais-biggest-bottleneck

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My biggest takeaways (for paid newsletter subscribers): https://www.lennysnewsletter.com/i/180365355/my-biggest-takeaways-from-this-conversation

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Where to find Alexander Embiricos:

• X: https://x.com/embirico

• LinkedIn: https://www.linkedin.com/in/embirico

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Where to find Lenny:

• Newsletter: https://www.lennysnewsletter.com

• X: https://twitter.com/lennysan

• LinkedIn: https://www.linkedin.com/in/lennyrachitsky/

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In this episode, we cover:

(00:00) Introduction to Alexander Embiricos 

(05:13) The speed and ambition at OpenAI

(11:34) Codex: OpenAI’s coding agent

(15:43) Codex’s explosive growth

(24:59) The future of AI and coding agents

(33:11) The impact of AI on engineering

(44:08) How Codex has impacted the way PMs operate

(45:40) Throwaway code and ubiquitous coding

(47:10) Shipping the Sora Android app

(49:01) Building the Atlas browser

(53:34) Codex’s impact on productivity

(55:35) Measuring progress on Codex

(58:09) Why they are building a web browser

(01:01:58) Non-engineering use cases for Codex

(01:02:53) Codex’s capabilities

(01:04:49) Tips for getting started with Codex

(01:05:37) Skills to lean into in the AI age

(01:10:36) How far are we from a human version of AI?

(01:13:31) Hiring and team growth at Codex

(01:15:47) Lightning round and final thoughts

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Referenced:

• OpenAI: https://openai.com

• Codex: https://openai.com/codex

• Inside ChatGPT: The fastest-growing product in history | Nick Turley (Head of ChatGPT at OpenAI): https://www.lennysnewsletter.com/p/inside-chatgpt-nick-turley

• Dropbox: http://dropbox.com

• Datadog: https://www.datadoghq.com

• Andrej Karpathy on X: https://x.com/karpathy

• The rise of Cursor: The $300M ARR AI tool that engineers can’t stop using | Michael Truell (co-founder and CEO): https://www.lennysnewsletter.com/p/the-rise-of-cursor-michael-truell

• Atlas: https://openai.com/index/introducing-chatgpt-atlas

• How Block is becoming the most AI-native enterprise in the world | Dhanji R. Prasanna: https://www.lennysnewsletter.com/p/how-block-is-becoming-the-most-ai-native

• Goose: https://block.xyz/inside/block-open-source-introduces-codename-goose

• Lessons on building product sense, navigating AI, optimizing the first mile, and making it through the messy middle | Scott Belsky (Adobe, Behance): https://www.lennysnewsletter.com/p/lessons-on-building-product-sense

• Sora Android app: https://play.google.com/store/apps/details?id=com.openai.sora&hl=en_US&pli=1

• The OpenAI Podcast—ChatGPT Atlas and the next era of web browsing: https://www.youtube.com/watch?v=WdbgNC80PMw&list=PLOXw6I10VTv9GAOCZjUAAkSVyW2cDXs4u&index=2

• How to measure AI developer productivity in 2025 | Nicole Forsgren: https://www.lennysnewsletter.com/p/how-to-measure-ai-developer-productivity

• Compiling: https://3d.xkcd.com/303

• Jujutsu Kaisen on Netflix: https://www.netflix.com/title/81278456

• Tesla: https://www.tesla.com

• Radical Candor: From theory to practice with author Kim Scott: https://www.lennysnewsletter.com/p/radical-candor-from-theory-to-practice

• Andreas Embirikos: https://en.wikipedia.org/wiki/Andreas_Embirikos

• George Embiricos: https://en.wikipedia.org/wiki/George_Embiricos: https://en.wikipedia.org/wiki/George_Embiricos

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Recommended books:

• Culture series: https://www.amazon.com/dp/B07WLZZ9WV

• The Lord of the Rings: https://www.amazon.com/Lord-Rings-J-R-R-Tolkien/dp/0544003411

• A Fire Upon the Deep (Zones of Thought series Book 1): https://www.amazon.com/Fire-Upon-Deep-Zones-Thought/dp/1250237750

• Radical Candor: Be a Kick-Ass Boss Without Losing Your Humanity: https://www.amazon.com/Radical-Candor-Kick-Ass-Without-Humanity/dp/1250103509

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Production and marketing by https://penname.co/. For inquiries about sponsoring the podcast, email podcast@lennyrachitsky.com.

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Lenny may be an investor in the companies discussed.