Developer and investor David Kalmanson said on Sept. 2, 2026, that he used the Codex AI agent over 26 days to recreate Red Alert 2: Yuri’s Revenge for native operation on iOS and macOS. The experiment tested whether Codex could rebuild an older game whose original source code was never published and is considered lost.

Codex, identified by Kalmanson as GPT-5.6 Sol, worked from the game’s EXE file and publicly available information about its gameplay and rules. Kalmanson described it as the hardest task he had given Codex.

Codex produced about 624,000 lines of C++

Kalmanson said in a post on X that Codex worked continuously for 26 days, made a large number of tool calls and produced about 624,000 lines of C++ code.

Several sub-agents helped analyze the executable, write code, run the game and identify bugs. During visual testing, Codex captured screenshots from Yuri’s Revenge videos on YouTube and compared them with screenshots from its own implementation, Kalmanson said.

According to Kalmanson, the resulting software resembles a conventional C++ project, with functions, classes, clear names and structured logic. The game retains minor visual bugs, but its core functionality works, he said. Online multiplayer was not implemented because Kalmanson chose to omit it.

Most of the project was managed from an iPhone

Kalmanson said he completed about 99% of his work through the ChatGPT app on his iPhone while taking a month-long road trip across the United States. His role mainly involved pointing out visual errors that the model’s computer-vision testing had missed.

He estimated that he could now complete a similar project in about a week. Running more agents in parallel accelerated the work, he said, but also exhausted the available usage limits more quickly.

Kalmanson put the cost at about $400

Kalmanson said the project cost about $400 in total. He used two ChatGPT Pro subscriptions priced at $200 each and also tested the API, although he said API expenses quickly became too high for a project of this scale.

He had previously ported Command & Conquer: Red Alert and Command & Conquer: Tiberian Dawn. Those projects were substantially easier because source code for both games is available online, he said.

The earlier ports prompted Kalmanson to test whether Codex could recreate an older game using only its executable. He said that after Red Alert 2 first ran on a Mac, he concluded that the same approach could potentially be used for many older games.

Kalmanson has not decided which game he may attempt next, but said the experiment demonstrated significant potential for using AI to restore older games.

Source: Incrypted