Abstract:

This video demonstrates the updated Codex CLI, powered by the GPT-5 Codex model. The presenters showcase an agentic workflow by tasking the CLI with converting a single-player game into a real-time multiplayer application. Key features highlighted include switching between model reasoning levels, managing file system access via sandboxed approval modes, and using web search to consult current documentation for deployment. The demonstration concludes with the CLI successfully deploying the modified game to Vercel, followed by a live test of the multiplayer functionality.

Codex CLI: From Single-Player to Deployed Multiplayer Game

• 0:00:02 Goal: Use the Codex CLI to make an existing single-player game multiplayer. The base game was also created by GPT-5 in a single prompt.
• 0:00:21 New Tooling: The demo showcases improvements to the Codex CLI, designed to use the agentic coding capabilities of the new GPT-5 Codex model.
• 0:00:48 Agentic Workflow: The process starts with a high-level prompt ("make a plan for making this game multiplayer"). Codex first generates a step-by-step plan before executing any code.
• 0:01:21 Transcript Mode: A transcript mode (Ctrl+T) provides a detailed view of the model's chain-of-thought and the specific commands it's running, for users who want to see the underlying process.
• 0:01:50 Model Switching: The /model command allows users to change the model's reasoning level, balancing speed for simple tasks against capability for complex ones that might take hours.
• 0:02:08 Sandboxed Approvals: The /approvals command controls file system access. The default auto mode sandboxes Codex to the current project directory. Other modes include read-only and full access for tasks like deployment.
• 0:02:48 Session Resume: The /resume command allows a user to continue any previous session.
• 0:03:45 Deployment with Web Search: To deploy the game, the CLI is instructed to use the /search command to look up the latest Vercel documentation, ensuring it uses current information.
• 0:04:04 Deployment Execution: After granting full access via the approvals command, Codex is told to use the Vercel command-line tool to deploy the application. It succeeds.
• 0:04:18 Live Multiplayer Test: The presenters test the deployed game on two separate laptops, confirming the real-time multiplayer functionality works as intended.