OpenAI Built Sora's Android App with Codex in Just 28 Days

2025-12-15

OpenAI built the Sora Android app in 28 days using Codex, an AI coding agent based on GPT-5.1, which wrote ~85% of the code. A team of four engineers leveraged Codex to scale output, achieving a 99.9% crash-free rate post-launch. Codex excelled at writing tests, translating logic across platforms (e.g., Swift to Kotlin), and navigating large codebases, acting like a senior engineer. The main challenges included Codex's difficulty with unguided architectural decisions and information inference, m

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