⚡️GPT5-Codex-Max: Training Agents with Personality, Tools & Trust — Brian Fioca + Bill Chen, OpenAI
From the frontlines of OpenAI's Codex and GPT-5 training teams, *Bryan* and *Bill* are building the future of AI-powered coding—where agents don't just autocomplete, they architect, refactor, and ship entire features while you sleep. We caught up with them at AI Engineer Conference right after the launch of *Codex Max,* OpenAI's newest long-running coding agent designed to work for 24+ hours straight, manage its own context, and spawn sub-agents to parallelize work across your entire codebase.
We sat down with Bryan and Bill to dig into what it actually takes to train a model that developers _trust_—why personality, communication, and planning matter as much as raw capability, how Codex is trained with strong opinions about tools (it loves rg over grep, seriously), why the abstraction layer is moving from models to full-stack agents you can plug into VS Code or Zed, how OpenAI partners co-develop tool integrations and discover unexpected model habits (like renaming tools to match Codex's internal training), the rise of *applied evals* that measure real-world impact instead of academic benchmarks, why multi-turn evals are the next frontier (and Bryan's "job interview eval" idea), how coding agents are breaking out of code into personal automation, terminal workflows, and computer use, and their 2026 vision: coding agents trusted enough to handle the hardest refactors at any company, not just top-tier firms, and general enough to build integrations, organize your desktop, and unlock capabilities you'd never get access to otherwise.
We discuss:
* What *Codex Max* is: a long-running coding agent that can work 24+ hours, manage its own context window, and spawn sub-agents for parallel work
* Why the name "Max": maximalist, maximization, speed _and_ endurance—it's simply better and faster for the same problems
* Training for *personality:* communication, planning, context gathering, and checking your work as behavioral characteristics, not just capabilities
* How Codex d
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