OpenAI has claimed that it built and shipped the Sora Android app in just 28 days, relying heavily on its AI coding agent, Codex.
The company said the initial production version of Sora for Android was developed between October 8 and November 5, 2025, by a four-engineer team working alongside Codex and consuming “roughly 5 billion tokens.”
The app launched publicly in November and reached number one on the Google Play Store on its first day, with Android users generating “more than a million videos in the first 24 hours.”
OpenAI engineers Patrick Hum and RJ Marsan wrote that the team deliberately avoided adding headcount under tight deadlines, citing the famous observation by American software engineer Fred Brooks that “adding more people to a late software project makes it later.”
Instead, each engineer worked with Codex to multiply output. “We assembled a strong team of four engineers – all equipped with Codex to drastically increase each engineer’s impact,” they said.
According to OpenAI, Codex handled an estimated 85% of the codebase, using an early version of the GPT-5.1-Codex model, which the company said is now available to developers via its CLI, IDE extension, and web app.
Despite the compressed timeline, OpenAI claims the app has a “99.9 per cent” crash-free rate.
The engineering team described treating Codex like “a newly hired senior engineer,” focusing human effort on architecture, system design, and user experience rather than implementation.
“We leaned on Codex to do a huge amount of heavy lifting inside well-understood patterns and well-bounded scopes, while our team focused on architecture, user experience, systemic changes, and final quality,” the authors wrote.
OpenAI said Codex excelled at reading large codebases, translating logic across platforms, and generating broad test coverage. “Codex is (uniquely) enthusiastic about writing unit tests,” the blog noted, adding that engineers frequently pasted CI logs into prompts to diagnose failures.
However, the company acknowledged limitations. Codex “isn’t yet great at inferring what it hasn’t been told,” and struggled with “deep architectural judgment” when left unguided.
To address this, the team invested heavily in documentation, such as AGENTS.md, to enforce patterns, coding standards, and tooling requirements.
One notable technique was to use Codex as a cross-platform translation layer rather than as a shared framework. “Forget React Native or Flutter; the future of cross-platform is just Codex,” the engineers wrote, explaining that Codex translated Swift logic from the iOS app into Kotlin while preserving behaviour.
As development accelerated, the bottleneck shifted from writing code to reviewing and coordinating parallel Codex sessions. “Our bottleneck in development shifted from writing code to making decisions, giving feedback, and integrating changes,” OpenAI said.
In the company’s State of Enterprise AI 2025 report, released a few days ago, the company stated that over the last six weeks, there was a 2x increase in weekly active Codex users. Further, the company observed a ~50% increase in Codex messages over the same period.
In October, Sam Altman, the CEO of the company, revealed that “Almost all new code written at OpenAI today is from Codex users.” He added that engineers in OpenAI complete 70% more pull requests (PRs) each week using Codex.
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