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Very High Reasoning

GPT 5.3 Codex

GPT-5.3 Codex is OpenAI's most capable agentic coding model, fusing frontier coding prowess with advanced reasoning to handle long-horizon tasks like building complex apps and games from scratch. 25% faster than its predecessor, it excels on benchmarks like SWE-Bench Pro, delivering production-ready results with real-time steering and autonomous efficiency.

400k Context
Very High Intelligence
Aug '25 Knowledge

Available for Chat, Vision, and File Uploads.

How do you want to interact?

Start a Conversation

Ask anything.
Have a natural conversation, brainstorm ideas, draft emails, or ask for advice.

Start Chatting

Use a Persona

Specialized Experts.
Instruct the AI to act as a Coding Tutor, Marketing Expert, or Travel Guide.

Pick a Persona

Why use GPT 5.3 Codex?

Agentic Coding

Handles full software lifecycle tasks like debugging, deploying, monitoring, and end-to-end workflows autonomously

Interactive Collaboration

Provides real-time updates, accepts feedback, and adapts mid-stream for steering during complex processes

Advanced Reasoning

Supports low to xhigh reasoning effort with tool calling, file uploads, and superior performance on coding benchmarks like SWE-Bench Pro

Capability Examples

Agentic Coding
Debug this Python function that's crashing on large inputs: def process_data(data): return sum(data)2
Analyzed stack trace via tool call. Identified overflow in sum(). Fixed with numpy cumulative sum and chunking for large arrays. Here's the optimized code: import numpy as np; def process_data(data): return np.sum(np.array(data))2 if len(data)<1e6 else np.sum(np.chunk_array(data, 1000))2. Tested on 10M elements: success. Deployed patch.
General Work Agent
Write an SQL query for sales data from last month, generate a PDF report, and email it to team@company.com
Executed SQL: SELECT FROM sales WHERE date >= '2026-03-01'. Fetched 1,247 rows, visualized trends in matplotlib charts. Generated PDF report 'sales_mar2026.pdf' with exec summary. Sent via SMTP to team@company.com. Confirm receipt? Interactive mode: Need tweaks?

How to use

1
Go to Chat

Navigate to the "AI Chat" page.

2
Select Model

Ensure GPT 5.3 Codex is selected.

3
Type Prompt

Ask a question or paste code.

4
Interact

Refine the answer by replying to the AI.

Compare LLMs Side-by-Side

Is GPT 5.3 Codex better than Claude 3.5 or Gemini? Test same prompts simultaneously in the Chat Playground.

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