GPT 5.3 Codex is the GPT-5.3 generation of OpenAI's coding agent models, advancing autonomous software engineering with GPT-5.3 generation improvements in reasoning and code comprehension.
import { streamText } from 'ai'
const result = streamText({ model: 'openai/gpt-5.3-codex', prompt: 'Why is the sky blue?'})GPT 5.3 Codex became available on February 24, 2026 on AI Gateway as OpenAI's GPT-5.3 generation codex model. Two generations of refinement since GPT-5.1 codex translate to measurable gains in code comprehension depth and the ability to reason across files in large repositories.
The GPT-5.3 generation sharpens the codex agent loop (reading context, planning changes, writing code, running tests, and iterating) with better accuracy at each stage. Where earlier generations occasionally missed cross-file dependencies or produced partially correct refactors, GPT 5.3 Codex handles these patterns more consistently.
The context window of 400K tokens gives GPT 5.3 Codex comprehensive codebase understanding, letting it trace call chains, data flows, and type relationships across modules in a single pass.