OpenAI’s Michael Bolin on Codex, Harness Engineering, and the Real Future of Coding Agents

Regarding the question of what matters most – the model or the harness – Michael Bolin is somewhere in the middle. Stronger models clearly pushed Codex to new heights. But without the right harness around them, those models would not be able to operate reliably, and – most importantly – safely on a real developer’s machine. At least, not yet. In this episode of Inference, I talk with Michael Bolin – lead for open source Codex at OpenAI – about the engineering layer that makes coding agents actually function: the agent loop, sandboxing, tool orchestration, and the design decisions that determine how much freedom an agent should have. In this conversation, we get into: What a harness actually is and why every coding agent needs one Can a model be enough for a reliable coding workflow Why do they build harness as small and tight as possible How Codex handles sandboxing and security across OS Why safety and security are not the same thing in agentic systems How coding agents are changing the daily workflow of developers Why documentation, tests, repo structure, and agents.md suddenly matter more Whether too much context can make an agent worse Why Michael believes the future may involve fewer tools, but more powerful ones If you’re trying to understand where coding agents are actually going, this episode is for you. Subscribe to the channel to be notified about Part 2, where we discuss what becomes of the software engineer in the age of agents. Chapters: 0:00 The New Inner Loop of AI Coding Agents 0:17 Introduction: Michael Bolin and Open Source Codex 1:17 What the “Harness” Is in AI Coding Agents 2:13 Security and Sandboxing for AI Agents 4:33 Codex Launch and Rapid Growth 5:25 The Codex App: A New Interface for Developers 6:36 How Coding Agents Change Developer Workflows 10:04 Writing Codebases and Documentation for AI Agents 12:44 Context Engineering and Prompting for Codex 16:02 Model vs Harness: What Really Matters for Agents 19:23 Multi-Agent Systems, Tools, and the Future of AI Development *Follow on*: https://www.turingpost.com/ *Did you like the episode? You know the drill:* 📌 Subscribe here and here (https://www.turingpost.com/subscribe) for more conversations with the builders shaping real-world AI. 💬 Leave a comment 👍 Like it 🫶 Thank you for watching and sharing! *Guest:*  Michael Bolin, tech lead on Codex, OpenAI https://www.linkedin.com/in/michael-bolin-7632712/ https://x.com/bolinfest https://github.com/openai/codex 📰 Transcript: https://www.turingpost.com/bolin1 *Turing Post* – AI stories from labs the Valley doesn't cover. https://x.com/TheTuringPost https://www.linkedin.com/in/ksenia-se Tags: #AI #OpenAI #Codex #CodingAgents #DeveloperTools #AgenticAI #SoftwareEngineering #HarnessEngineering #Harness