GPT-5.1 Codex vs Claude Sonnet 4.6 - which to choose

Two models dominate most "which one should I code with" debates right now: OpenAI's GPT-5.1 Codex and Anthropic's Claude Sonnet 4.6. Both are excellent. The honest answer is that the right pick depends on your workflow, not on a leaderboard. Here's how they actually differ in day-to-day use, and how to settle it for your own codebase without guessing.

The short version

• GPT-5.1 Codex is tuned for agentic coding: long autonomous runs, tool calling, terminal work, and multi-file edits where it keeps going until the task is done.
• Claude Sonnet 4.6 is a strong all-rounder with sharp code reasoning, careful instruction-following, and a reputation for clean, reviewable diffs and clear explanations.

If your work is "drive an agent through a repo and let it run," Codex tends to feel more at home. If your work is "reason carefully about a tricky change, explain it, and keep edits surgical," Sonnet 4.6 often edges ahead.

Head to head

These are tendencies, not laws. Model quality shifts with prompt, tooling, and task. That's exactly why a real test on your code beats any generic benchmark.

When to pick GPT-5.1 Codex

Reach for Codex when the task is open-ended and tool-heavy: scaffolding a feature across many files, running tests and fixing what breaks, refactoring with a build loop, or anything where you want the model to keep iterating with minimal hand-holding. It's the natural fit for CLI agents that execute commands and read results back.

When to pick Claude Sonnet 4.6

Reach for Sonnet 4.6 when correctness and clarity matter more than autonomy: debugging subtle logic, writing code you'll review line by line, designing an API, or explaining why a change is safe. It's also a good default when you want the model to respect tight constraints and not "improve" things you didn't ask it to touch.

Don't choose - test both

You don't have to commit to one. With AnyModel you get one OpenAI-compatible endpoint and one API key that reaches GPT, Claude, Gemini, DeepSeek, GLM, Kimi, Qwen, and Grok. Switching models is a one-field change - the model id - so you can run the same prompt through both and compare output directly. See the full lineup on the models page or browse side-by-side notes on /compare.

Point any OpenAI-compatible client at the gateway:

curl https://anymodel.org/v1/chat/completions \
  -H "Authorization: Bearer $ANYMODEL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"gpt-5.1-codex","messages":[{"role":"user","content":"Refactor this function and explain the change."}]}'

Swap "gpt-5.1-codex" for "claude-sonnet-4-6" and rerun. Same key, same endpoint, nothing else to configure.

Using a supported CLI? One line installs it against AnyModel:

bash <(curl -fsSL "https://anymodel.org/i?tool=codex") <YOUR_API_KEY>

Use tool=claude for Claude Code. The installer supports codex, claude, opencode, and hermes. For Cursor, Windsurf, Zed, Cline, Aider, Continue, or Gemini CLI, do a manual OpenAI-compatible setup: base URL https://anymodel.org/v1 plus your key.

Cost and privacy notes

There's no subscription and no minimums - you pay per token, so running both models for an honest A/B costs only the tokens you spend. New accounts start with 1,000,000 free tokens (6,000,000 total if you link Telegram), no credit card. If you handle sensitive code, Ghost Mode is opt-in zero-retention: we don't store prompts or responses, only a token counter. (Note: the model provider still receives your prompt, so this isn't "100% privacy" - it just means we keep nothing on our side.)

Bottom line

Pick GPT-5.1 Codex for autonomous, tool-driven coding; pick Claude Sonnet 4.6 for precise, reviewable, well-explained changes. Better yet, keep both a model id apart and let your actual results decide. More breakdowns like this live on the blog.

Ready to try both on your own code? Create a free account and start with a million tokens, no card required.