Released 56 days after GPT-5.2 · All OpenAI releases
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.
Call GPT-5.3 Codex on Opper with the OpenAI SDK. Sign up without a credit card. Get started
GPT-5.3 Codex runs on 2 different routes through the Opper gateway. Compare residency, zero data retention and training posture at a glance, with full data-handling detail per route below.
GPT-5.3 Codex runs on 2 independently monitored routes through the Opper gateway. A direct integration leaves you on one of them, the gateway serves whichever is healthy.
Measured over the last 30 days from each provider's official status feed via StatusGator. Refreshed hourly. See uptime for every provider Opper monitors.
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 with abuse monitoring: nothing is logged or used for training; content flagged by abuse monitoring is held for review. No training on customer data. EU; DPA available.
Zero data retention with abuse monitoring: prompts and outputs are kept for up to 30 days for abuse monitoring only, and are not used for training. No training on customer data. US; SCCs; DPA available.
Independent benchmark scores — 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. Opper is drop-in compatible with the OpenAI, Anthropic and Google AI SDKs.
GPT-5.3 Codex is a premium model on Opper. Sign up needs no credit card: you get an API key straight away and the free models work in the playground and the API. Add a card to use premium models, pay-as-you-go with no minimum.
Copy this and paste it into a coding agent like Claude Code, Cursor or Codex 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: "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.
