Simplex rethinks software development with Codex

Results

• 70% less time needed to develop each screen with Codex
• 40% less time needed to design each screen with Codex
• 17% less time needed for internal integration testing with Codex

Simplex is a technology partner that works across consulting, systems development, and operations. To improve productivity in systems development, the company has quantitatively measured the impact of generative AI and applied those learnings across multiple projects. Building on that experience, Simplex is now evaluating generative AI use across all projects and advancing AI-native delivery in applicable projects, with the goal of improving productivity across the organization.

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. Building on that work, the company adopted ChatGPT Enterprise across the organization and selected Codex as its primary coding agent, accelerating an effort to rethink how software development gets done.

In traditional software development, tasks such as interpreting design documents, deciding how to implement a feature, and fixing defects often depend on the experience of individual contributors. As generative AI started to spread, it was often used as an assistive tool. More recently, agentic systems have made it possible to delegate multi-step tasks to AI, moving beyond support to take on work that advances projects directly.

Codex's role at Simplex goes beyond code generation. The company uses it across design and testing, including front and back-end code generation from design documents, creation of test code, and fixes for issues found during internal integration testing.

“Codex has made it easier for smaller teams to move design work forward,” says Ujihiro. “Roles are becoming clearer on the ground: people focus on final decisions and accountability for quality, while AI handles implementation, review, and fixes.”

Simplex's experience highlights several lessons: validate impact quantitatively, treat adoption as an operating model rather than just a tool, and define where AI should execute work versus where people retain final accountability.

Simplex is not trying to replace each step of the traditional process one-for-one. Instead, the company is working to redesign the development process itself around AI, exploring approaches that define rules up front and improve quality through repeated integration and automated evaluation.