GPT 5.3 Codex Now Available

Vercel has introduced GPT 5.3 Codex to its AI Gateway platform, a new model designed specifically for developers building AI-powered applications. The model merges the coding expertise of GPT-5.2-Codex with the reasoning depth of GPT-5.2, delivering a more capable tool for complex software development tasks.

Key Improvements

Performance and Efficiency:

• 25% faster execution than its predecessors
• Improved token efficiency for cost-effective operations
• Built for long-running agentic work requiring research, tool use, and multi-step execution

Developer Experience:

• Better understanding of underspecified prompts in web development contexts
• Defaults to production-ready output without requiring excessive refinement
• Mid-task steering capability without losing context, enabling iterative development workflows

How to Use

To integrate GPT 5.3 Codex into your applications, set the model identifier to openai/gpt-5.3-codex in the Vercel AI SDK:

import { streamText } from 'ai';

const result = streamText({
  model: 'openai/gpt-5.3-codex',
  prompt: 'Research our current API architecture, identify performance bottlenecks, refactor the slow endpoints, add monitoring, and deploy the changes to staging.',
});

AI Gateway Features

The model integrates with AI Gateway's existing capabilities, including built-in observability, Bring Your Own Key support, intelligent provider routing, and automatic retries for improved reliability and uptime beyond individual provider guarantees.