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Simplex rethinks software development with Codex

Codex — After ChatGPT launched in 2022, Simplex established a center of excellence in 2023 to create the foundations for employees to use AI and to validate AI-native development processes. To scale that shift, Simplex adopted ChatGPT Enterprise as the foundation for company-wide deployment and uses Codex as its main coding agent. After ChatGPT launched in 2022, Simplex established a center of excellence in 2023 to create the foundations for employees to use AI and to validate AI-native development processes.

Agent or tool
ChatGPT
Topic
Software Development
Reported on
Case study (OpenAI)
Added
2026-11-11

Why it matters

Coding agents are moving from autocomplete to doing whole tasks: reading a codebase, making a plan and changing many files. This case is a concrete example of where that works in practice. It is one of 221 sightings filed under Software Development on Agent Sightings (number 71 by interest), and one of 145 involving ChatGPT.

How you could try it

Here is a reusable prompt, written by us in our own words, that captures the task. Paste it into ChatGPT or any similar agent and adjust the details to your situation.

I want a coding agent to plan first, work on a branch, and show me the diff before anything is merged. The tool in the source case was ChatGPT.

Saved

Tip: Work on a fresh branch, ask for a plan before edits, and review the diff and test results before merging.

Source

Read the original first-hand account on Case study (OpenAI): https://openai.com/index/simplex. Our summary is a paraphrase; details are in the source.

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