OpenAI Codex Review: Legacy AI code model

Overview

OpenAI Codex was the AI model that powered the first version of GitHub Copilot. Launched in 2021, it was a descendant of GPT-3 fine-tuned specifically for code generation. Codex could translate natural language to code across dozens of programming languages, with particular strength in Python.

Codex was deprecated by OpenAI in 2023 and is no longer available as a standalone API. Its capabilities have been absorbed into and surpassed by GPT-4o, which is better at code generation, reasoning, and understanding complex codebases. The "Codex" name now lives on in Codex CLI — OpenAI's open-source terminal coding agent — but that's a completely different product.

If you're looking for OpenAI's current code generation capabilities, use GPT-4o via the API, ChatGPT, or GitHub Copilot (which now uses GPT-4o under the hood). If you're looking for an OpenAI terminal coding agent, use Codex CLI.

Key features

• Natural language to code — translate English descriptions into working code across multiple languages
• Python specialization — particularly strong at Python code generation and data science tasks
• Multi-language support — worked with JavaScript, Go, Ruby, TypeScript, Shell, and more
• API access (deprecated) — was available as a standalone API for code generation tasks
• Copilot integration (historical) — powered the original GitHub Copilot completions

How it fits your workflow

Codex is no longer available. Here's what to use instead:

1. For code generation via API — use GPT-4o. It's better than Codex in every way: more accurate, better reasoning, broader language support.
2. For inline completions — use GitHub Copilot (powered by GPT-4o) or Cursor (supports multiple models including GPT-4o).
3. For terminal agent workflows — use Codex CLI, OpenAI's open-source terminal coding agent. Despite the name, it's a completely new product, not a continuation of the Codex model.
4. For chat-based coding — use ChatGPT with GPT-4o. It can generate, explain, and debug code across any language.

Everything Codex did, GPT-4o does better. There's no reason to seek out the deprecated Codex model.

Pricing

Codex API is no longer available. Current OpenAI pricing for code generation:

• GPT-4o — $2.50/$10 per 1M input/output tokens
• GPT-4.1-mini — $0.15/$0.60 per 1M input/output tokens (cheaper, good for simpler tasks)
• ChatGPT Plus — $20/month for chat-based access to GPT-4o
• GitHub Copilot — $10/month (Individual) for editor-integrated GPT-4o access

Strengths

• Historical significance — Codex proved that AI could generate useful code from natural language
• Powered the first version of GitHub Copilot — launched the entire AI coding assistant category
• Strong Python performance — was the best Python code generator of its era
• OpenAI's commitment to code AI — Codex demonstrated OpenAI's long-term investment in code generation

Limitations

• Deprecated — no longer available, replaced by better models
• Weaker than modern alternatives — GPT-4o, Claude, and Gemini all outperform Codex
• Limited context window — 4K tokens vs GPT-4o's 128K
• No codebase awareness — could only see what you sent it, not your project structure
• No agent capabilities — could generate code but couldn't edit files, run tests, or iterate

Who it's for

OpenAI Codex is for historians and completionists. If you're building an AI coding tool today, use GPT-4o, Claude, or Gemini — they're better in every dimension. If you're curious about the history of AI coding tools, Codex is an important milestone — it proved the concept and launched the category. But for actual development work, it's been obsolete since 2023.

Verdict

OpenAI Codex was important. It launched the AI coding revolution and proved that language models could generate useful code. But it's been replaced by models that are faster, smarter, and more capable. If you're evaluating AI coding tools today, look at GPT-4o (via API, ChatGPT, or Copilot), Claude (via Claude Code or API), or Gemini (via Cody or API). Codex belongs in the history books, not your development workflow.