Building Pi, and what makes self-modifying software so fascinating

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Mario Zechner is the creator of Pi, a minimalist, self-modifying AI coding agent, that is the foundation upon which OpenClaw (created by Peter Steinberger) is built. Meanwhile, Armin Ronacher is the creator of Flask, and a longtime user of Pi. The pair are also friends.

I sat down with Mario and Armin for the latest episode of the Pragmatic Engineer Podcast for an interesting conversation about AI and their reservations about it – even though both are heavily invested in building AI-powered tools.

Mario explains why he built Pi, and gives his take on why it has become so popular. Armin walks us through how he uses AI tools, including building a game with Pi, and why he always puts human judgment firmly at the heart of his approach.

We cover the risks of over-automation, the limits of agentic workflows, and why strong engineers with informed judgment still matter. We also get into the challenges of working with code written by non-engineers, and whether open source can withstand a tidal wave of agent-generated code.

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Timestamps

(00:00) Intro

(07:30) How Mario, Armin, and Peter Steinberger met(15:15) How 30 dev teams use AI agents: learnings

(21:50) The importance of judgment

(24:26) Challenges when non-engineers write code

(28:30) Downsides of over-automation

(32:18) Pi

(48:09) OpenClaw + Pi

(50:54) “Clankers”

(57:32) Open source and AI

(1:00:22) Complexity as the enemy

(1:02:50) Building an AI-native startup

(1:11:52) “Slow the F down”

(1:16:40) MCPs vs. CLI

(1:25:03) Predictions and staying up to date

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The Pragmatic Engineer deepdives relevant for this episode:

• The impact of AI on software engineers in 2026: key trends

• Cycles of disruption in the tech industry

• The AI engineering stack

• The creator of OpenClaw: "I ship code that I don't read"

• What is inference engineering? Deepdive

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