Building Pi, and what makes self-modifying software so fascinating
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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• Sonar – The makers of SonarQube, the industry standard for automated code review. https://www.sonarsource.com/pragmatic...[…]egory=Paid&s_source=Paid%20Other&s_origin=pragmaticengineer
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The Pragmatic Engineer deepdives relevant for this episode:
• The impact of AI on software engineers in 2026: key trends https://newsletter.pragmaticengineer....
• Cycles of disruption in the tech industry https://newsletter.pragmaticengineer....
• The AI engineering stack https://newsletter.pragmaticengineer....
• The creator of OpenClaw: "I ship code that I don't read" https://newsletter.pragmaticengineer....
• What is inference engineering? Deepdive https://newsletter.pragmaticengineer....
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Where to find Mario Zechner:
• X: https://x.com/badlogicgames
• LinkedIn: / mariozechner
• Website: https://mariozechner.at
Where to find Armin Ronacher:
• X: https://x.com/mitsuhiko
• LinkedIn: / arminronacher
• Website: https://mitsuhiko.at
• Blog: https://lucumr.pocoo.org
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In this episode, we cover:
(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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See the transcript and other references from the episode at https://newsletter.pragmaticengineer....
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