Custom GPTs are going on 11 December. Here's what you need to know

If you've spent the last couple of years building custom GPTs, there's a date you need in your diary: 11 December 2026.

That's the day OpenAI is retiring custom GPTs. Not changing them, not renaming them. On the retirement date, custom GPTs and their GPT pages are scheduled to become inaccessible.

OpenAI announced it in the ChatGPT release notes on 11 September, and it applies to every ChatGPT plan. So this post is everything you need to know: what's happening, why, what comes across to the new setup, what gets left behind, and exactly what to do before the date so you don't lose the work.

There's a second post coming on what I'd actually build instead. This one is about making sure nothing you rely on disappears in the meantime.

What's happening, in plain words

Custom GPTs are being replaced by plugins.

OpenAI describes a plugin as a reusable package for a workflow that can include skills, apps, or both. A skill is the instructions for a job. An app connects ChatGPT to something outside it, like your Google Drive or your CRM. Plugins work across ChatGPT and Codex, OpenAI's coding tool, so the same package works in more than one place, where a GPT only lived inside a chat.

If you've read my post on how to build a Claude skill, this will sound familiar. The whole industry is moving the same way: the instructions for a job get written down once, as a skill, and the AI reaches for them when it needs them.

The dates

These are OpenAI's dates. They say timing can vary by account or workspace, so watch for the notice inside ChatGPT too.

• 11 September 2026 - the retirement was announced.
• 22 September 2026 - migration started rolling out to affected Enterprise workspaces.
• 26 October 2026 - Enterprise workspaces can no longer create new custom GPTs.
• 11 December 2026 - the standard retirement date. Custom GPTs and their pages become inaccessible.
• 11 February 2027 - the later date, only for Enterprise workspaces that have an approved deferral.

If you're on Plus or a personal plan, 11 December is your date.

What comes across when you migrate

OpenAI has built a migration button. When it's available for your account, you go to My GPTs, choose the GPT and click Migrate to plugin.

Three things come across:

1. Your instructions become a skill inside the new plugin.
2. Your knowledge files are copied into the plugin's reference files.
3. Your connected apps are added to the plugin as apps.

It uses the latest published version of your GPT. If you've got edits sitting in a draft that you never published, they don't come with it.

What doesn't come across

This is the part that will catch people out, so read it slowly.

Your conversations stay with the old GPT. Migration doesn't move your chat history into the plugin. You can keep using the original GPT until the retirement date, but after that it's gone. If there's anything in those chats you need, copy it out before 11 December.

Custom actions don't transfer. If your GPT called an outside tool through an action, that has to be rebuilt, using a supported connector or a custom MCP server. MCP is the standard way an AI connects to another tool. For a simple GPT that's nothing to worry about. For one that books appointments, writes to a spreadsheet or talks to your CRM, it's real work.

The model you picked doesn't come with it. If you set your GPT to use a particular model, the plugin won't remember that.

Your sharing settings don't come with it. A migrated plugin starts private. Nobody who used your GPT gets access to the replacement until you share it with them yourself. If you've got a GPT in the GPT Store, or a link you've handed to clients or a community, every one of those people loses it on 11 December unless you send them the new one.

Conversation starters don't carry over one-to-one either, so check them once you've migrated.

And one more thing to know before you press the button: once you migrate, the original GPT becomes read-only. You can still use it until the retirement date, but every edit from then on happens in the plugin. Finish any changes you want to make first.

Why the same instructions might not give you the same answers

OpenAI says it plainly: "A migrated plugin may respond differently." They recommend you "retest familiar prompts, reference-material use, required output formats and integrations" before you rely on it.

That makes sense when you think about how it works. A custom GPT carried its instructions into every single chat. A skill sits in the background until the AI decides it needs it. Same words, different way of being used, so the answers can drift. That's not a reason to panic. It's a reason to test before your clients or your community notice.

What to do before 11 December

Do this once for every GPT you rely on. It's the same five steps whether you've built one GPT or twenty.

Step 1 - List every GPT you use, and whose it is

Open My GPTs and write down every GPT you've built. Then think about the ones you use that someone else built, because those matter too.

For each one, note three things: do you own it, does anyone else use it, and does it connect to anything outside ChatGPT.

If you use a GPT that somebody else built, you can't migrate it. Message the creator and ask them for the link to their plugin once it's ready. If they don't send you one, you won't have it after 11 December.

Step 2 - Back up what's in it

Open the GPT, click Edit, then the Configure tab.

1. Copy your instructions into a document you own.
2. Make sure you still have the original copies of every knowledge file you uploaded.
3. Write down any actions it uses and what each one does.
4. Copy out anything from your past chats with it that you'll still need.

This takes ten minutes and it means that whatever happens with the migration, you never have to rebuild that GPT from memory.

Step 3 - Build a test before you migrate

This is the step most people will skip, and it's the one that tells you whether the plugin actually works. Open the original GPT and paste this in:

I'm about to migrate you to a plugin & I need to check the new version works the same way.

Look at your instructions & knowledge files & write me 5 test prompts:
- the 3 jobs I'd use you for most often
- 1 job that uses my knowledge files
- 1 tricky case where you'd need to follow my rules carefully

For each one, write the prompt exactly as I'd type it, then answer it the way you normally would.

Keep the prompts & your answers together so I can run the same prompts in the new plugin & compare.

Save the prompts and the answers in the same document as your backup.

Step 4 - Migrate and run the same test

1. Go to My GPTs.
2. Choose the GPT.
3. Click Migrate to plugin.

If you don't see the button yet, migration hasn't reached your account. Keep an eye out for the notice inside ChatGPT rather than assuming it works the same way as the Enterprise rollout.

Once it's migrated, open the new plugin, run the same five test prompts and put the answers side by side with the old ones. If something's off, adjust the skill's instructions and run the test again. If your GPT used actions, this is where you'll find out what needs rebuilding.

Step 5 - Share it again

Remember the plugin starts private. If anyone used your GPT, share the plugin with them and send them the new link. Installing a plugin and sharing it are separate steps, so tell them they'll need to install it on their side too.

If you've got a link to your GPT in a lead magnet, a welcome email, a course or a client handover document, update it now. Every one of those links stops working on 11 December.

The catch, and what I'd do about it

The honest catch is the actions. A plugin can do far more than a GPT could, but anything your GPT did through a custom action doesn't come across, and rebuilding it with a connector or an MCP server is technical work if you've never done it before.

There's a bigger question underneath it too. If you have to rebuild the thing anyway, where do you want to rebuild it? That's the next post: the solution, and what I'd do instead. In the meantime, the post on how to build a Claude skill shows you what a skill looks like when you own the file.

If you've built GPTs for clients

If you build for clients, every GPT you've handed over is about to stop working, and most of your clients won't know.

Tell them before they find out the hard way. Back up each one, migrate it, test it, share it again, and update any links you gave them. If a client's GPT relied on actions, that's a rebuild, and it's a piece of work in its own right. This is exactly the kind of job you get paid for knowing how to do.

Start with one

Don't try to move everything this week.

Pick the GPT you'd miss most, the one you or a client opens every day, and do the five steps on that one. Back it up, write the test, migrate it, run the test, share it again. Once you've done one, the rest are the same steps on repeat.

If you haven't got your AI brain set up, that's the foundation for all of this: start here.