Run Claude Code with GPT 5.6 Sol in 5 Minutes

What if you could keep everything you love about Claude Code, the harness, the tools, the workflow, and swap the model inside it for GPT 5.6 Sol? That is exactly what I show you in this walkthrough. I built a GitHub repository called Claudex that turns this into a five-minute setup, and your own Claude Code instance can walk you through the whole installation.

What you need

• Claude Code installed in the terminal. This will not work inside the desktop application of Claude. You can even use Claude Code to help you install Claude Code in the terminal, which is great.
• An OpenAI ChatGPT account. To use Claudex you do not even need a Claude account; your ChatGPT account is enough to set everything up.
• The Claudex repository link, which does the rest.

1. Run GPT 5.6 Sol inside Claude Code (0:00)

The idea sounds strange at first: Claude Code, running an OpenAI model. But the repository I created makes it real. You can think of Claudex simply as step-by-step instructions that are going to be followed by your Claude Code. And I was not alone in creating this: it builds on top of work that was partly created by someone else. I just built on top of it.

2. Open the Claudex GitHub setup (0:09)

Start from the repository:

https://github.com/migueltorrezd/claudex

Feel free to go ahead and read everything that is happening in the background. There is also a diagram inside the GitHub repo that I created, so you can really understand what happens behind the scenes before you run anything.

3. Requirements and terminal setup (0:36)

The one hard requirement worth repeating: this runs in the terminal, not the Claude desktop app. If you only ever used the desktop application, this is the moment to get Claude Code installed in your terminal, and Claude itself can guide you through that installation.

4. Let Claude Code explain the repository (0:53)

Instead of following the instructions manually, hand the link to your main Claude Code instance and ask:

Hey Claude, can you please explain to me what's inside of this GitHub link?

It fetches the information and breaks it down for you. The repository has step-by-step instructions that Claude Code can follow to do the entire setup. It is a five-minute setup, and it actually asks you how you want it configured for you.

5. See CCX running GPT 5.6 Sol (2:05)

Once it installs in your terminal, you get a new default command called CCX:

ccx

When I run it in my main terminal, it says GPT 5.6 Sol right at the top. It is using GPT 5.6 Sol for everything: the main agent, the subagents, the background tasks, literally everything. It also lets you select directly the models you want to use. In my case, I run Sol High.

6. How the harness-and-brain swap works (2:43)

Why can you even do this? Because Claude Code is not actually a brain, it is a body. Inside that body is the LLM actually driving it. The body itself, the harness, is fantastic. Think of it as the Iron Man suit. Normally the Claude brains sit inside, but because we know how the body is built, you can literally swap the brains out and put a new brain in. That is why you can use Claude Code with your OpenAI subscription.

7. Why use Claude Code with OpenAI models (3:30)

Claude Code is probably the better harness for coding. It has a lot of features that are really nice. So it is always worth testing whether you prefer Claude Code driven by GPT 5.6 Sol, or Codex from the desktop application. Both are valid choices, and now you can actually compare them on your own work instead of guessing.

8. Final setup and next steps (3:56)

I created everything to make this as simple and as customizable as possible. Run the setup, try CCX on a real task, and see which combination fits how you work. If it helps you, star the GitHub repository so more people can find it.

Pitfalls and tips

• Do not try this inside the Claude desktop app. It only works with Claude Code installed in the terminal.
• You do not need a Claude account for this path. Your OpenAI ChatGPT account is enough.
• Read the repository and its diagram before running the setup, so you understand exactly what is being installed and why.

Where to go next

• Prefer keeping Fable 5 in charge and delegating execution to GPT 5.6 Sol instead of replacing the brain entirely? Read Make Claude Fable 5 Use GPT 5.6 Sol: Here's How.
• Curious what OpenAI shipped on the app side? See ChatGPT Work Just Dropped, Here's Everything You Need to Know.