GPT-5.3 Codex is OpenAI's most advanced agentic coding model, trained with reinforcement learning on real-world software engineering tasks. It reaches state-of-the-art performance on SWE-Bench Pro and far exceeds prior results on Terminal-Bench 2.0, both rigorous evaluations of production software engineering, while using fewer output tokens than any prior OpenAI model. The model pairs frontier coding performance with general reasoning to support long-horizon technical work across the software lifecycle, including debugging, deployment, monitoring, documentation, tests, and metrics. It reliably completes complex tasks such as large refactors, code migrations, and feature implementations without losing context. With a 272k token context window, GPT-5.3 Codex excels at writing, reading, and modifying code across large projects. It supports structured output and tool use for integration with development workflows and automation systems.
GPT-5.3 Codex runs on 2 different routes through the Opper gateway. Compare residency, ZDR, and training posture at a glance β full data-handling detail per route below.
Training posture across routes: No training on prompts by default.
Each route hosting GPT-5.3 Codex has its own privacy posture, residency, and GDPR terms. Postures are maintained by Opper with a last-verification timestamp.
Zero data retention is available via Opper Enterprise contract. No training on customer data. EU; DPA available.
Zero data retention is available via Opper Enterprise contract. No training on customer data. US; SCCs; DPA available.
Independent benchmark scores β composite indices for reasoning, coding, and math, plus individual eval scores where available.
Call GPT-5.3 Codex through the Opper gateway with one API key. Let your coding agent set it up, or call it directly β Opper is drop-in compatible with the OpenAI, Anthropic, and Google AI SDKs.
Copy this and paste it into your coding agent β Claude Code, Cursor, Codex, and more β and it'll wire up Opper for you.
import OpenAI from "openai";const client = new OpenAI({apiKey: process.env.OPPER_API_KEY,baseURL: "https://api.opper.ai/v3/compat",});const completion = await client.chat.completions.create({model: "openai/gpt-5.3-codex",messages: [{ role: "user", content: "Hello" }],});console.log(completion.choices[0].message.content);
Side-by-side on privacy, EU hosting, pricing, and benchmarks.
