OpenAI quickly developed and launched the Sora Android app by leveraging its AI coding agent, Codex. The app was built in a notably short period from 2025-10-08 to 2025-11-05 by a four-engineer team working closely with Codex. Upon release, the app claimed the top spot on the Google Play Store and generated over a million videos within the first 24 hours.
Codex's Role in Development
Codex played a crucial role by significantly boosting productivity. The application development process included Codex handling approximately 85% of the coding tasks using the GPT-5.1-Codex model. This approach allowed the team to maintain a lean setup without expanding resources significantly under tight deadlines. Despite the aggressive schedule, Codex contributed to a 99.9% crash-free experience in the released app.
- Development commenced on 2025-10-08.
- Public launch occurred in November 2025.
- The app reached the top of Google Play on its first day.
- Over a million videos were created by users within 24 hours of launch.
- Codex developed roughly 85% of the codebase.
Challenges and Learnings
The engineering team compared Codex to a senior engineer who handled intricate tasks such as large codebase readings, cross-platform code translation, and unit test generation. Human engineers focused on system design and user experience. However, Codex faced challenges with unstated requirements and architectural judgment, leading the team to emphasize thorough documentation, like AGENTS.md.
As development progressed, the bottleneck shifted towards coordinating parallel production sessions and reviewing Codex outputs. OpenAI's report, 'State of Enterprise AI 2025', noted a doubling of weekly active users for Codex and a 50% rise in Codex message volume. CEO Sam Altman stated that most current code at OpenAI is generated by Codex users, which improves engineers' ability to complete more pull requests weekly.
