OpenAI’s Michael Bolin on Codex, Harness Engineering, and the Real Future of Coding Agents
Inference by Turing Post
Model vs Harness: Keeping the Harness Small
Michael argues for a minimal harness exposing powerful primitives (terminal) while relying on sandboxing for safety.
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
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*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
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