OpenAI Codex Made Crystal Clear · chapter 2: One Agent, Four Surfaces
The big schema
2026-09-06
One agent core (a model wrapped in a harness) is met on four surfaces: the CLI on your machine, the IDE extension in your editor, Codex cloud in OpenAI's containers, and code review on your GitHub pull requests. The desktop and mobile apps are windows onto the same agent, not a fifth one. The chapter pins mark where this book zooms in.
Below: the paragraph from the book that builds this idea, then the diagram itself (Figure 2.1), and a recap. About a minute of reading.
Here is the second idea, and it answers the most basic question readers bring to this book: not "what is Codex" but "which Codex do I use". There is one agent, and it shows up on four surfaces: a surface is a place where you meet the agent, and each one hosts the same model-plus-harness core somewhere different. Figure 2.1 is the map. It is the most important diagram in this book: every later architecture figure zooms into one region of it, so when a figure in chapter 7 looks familiar, that is deliberate.
Recap
- The idea: One agent core (a model wrapped in a harness) is met on four surfaces: the CLI on your machine, the IDE extension in your editor, Codex cloud in OpenAI's containers, and code review on your GitHub pull requests.
- The picture: Figure 2.1, from chapter 2 ("One Agent, Four Surfaces") of OpenAI Codex Made Crystal Clear.
- Go deeper: the chapter builds this step by step, with recipes and sources at the end.
This diagram is one of many in OpenAI Codex Made Crystal Clear.
Every chapter opens with the gist, draws the hard ideas, and ends with recipes and sources.
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