Custom GPTs Are Ending — Do This Now

Cross-posted from Paragon AI MAG (https://paragonaimag.substack.com/p/custom-gpts-are-ending-do-this-now). A plain-English explainer: what a custom GPT is, how plugins and Gemini Skills replace it, what does not transfer, and the five steps to save your workflows. Video: https://youtu.be/kiTxa9Fb2EA

Listen to the podcast episode: https://redcircle.com/shows/cbce814a-d451-4913-a015-fe05b4d0e059/episodes/c9e53167-172c-4331-bc22-5dea067532fa

By Paragon AI MAG — Episode 3 of "How the AI Tools You Use Actually Work"

OpenAI is retiring every custom GPT on December 11, 2026. More than 3 million of them were built. And in the same weeks, Google is turning Gemini Gems — its version of the same idea — into Skills on November 17, 2026.

If you built your own ChatGPT — a tutor, a work helper, a writing coach — this is the moment to save it. Here is what is happening, what replaces it, and the five steps that protect your work.

What a custom GPT actually is

In November 2023, at OpenAI's first DevDay, the company showed that anyone could build a custom version of ChatGPT by typing plain words. No code. The pitch was simple: GPTs are like apps for ChatGPT.

A custom GPT is just three things:

1. Instructions — plain written rules for how it should behave, every time. Role, audience, steps, format, and what to refuse.
2. Knowledge files — up to 20 documents it can look things up in: your notes, your price list, your handbook.
3. Capabilities and actions — built-in tools like web search and image generation, or a connection to another app through an API.

The GPT Store opened on January 10, 2024. By then, users had already created more than 3 million custom GPTs; about 159,000 are public in the store. OpenAI says weekly use of custom GPTs and Projects grew 19 times in 2025, and about 20 percent of enterprise ChatGPT messages now go through a custom GPT or a Project. Coding co-pilots, marketing strategists, company FAQ bots — entire startups were built on top of these assistants.

What is changing, and when

OpenAI announced the retirement on September 11, 2026, in the ChatGPT release notes. The standard retirement date is December 11, 2026: custom GPTs and their pages become inaccessible. Some Enterprise workspaces with an approved delay get until February 11, 2027. Personal accounts (Free, Go, Plus, and Pro) already cannot create or publish new GPTs.

On the Google side, Gems become Skills starting November 17, 2026, automatically. Gems turn read-only that day and are removed on December 17, 2026. Skills are called up inside Gemini chats.

OpenAI says all dates are subject to change — follow the notice inside your own account.

What replaces them

The replacement is plugins. A plugin bundles reusable instructions (called skills), reference files, and connected apps — the same three ingredients, in a new container.

Migration works from My GPTs: press Migrate to plugin when the button appears. The tool uses the latest published version of your GPT, and only that version. Your instructions become a skill inside the new plugin, your knowledge files copy across as reference files, and your connected apps come along.

But not everything moves. Custom actions do not transfer at all — if your GPT calls your own API, that connection has to be rebuilt. Sharing settings, conversation starters, capability settings, and the chosen model do not transfer either. The new plugin starts private; making it public needs a separate review by OpenAI.

For anything new, OpenAI says: build it with Plugin Creator, not as a GPT. The same logic applies on Google's side — build Skills, not Gems — and Claude Projects offer the same instructions-plus-files recipe for people who work in Claude.

The five steps that save your workflows

1. Open My GPTs and list what you built. Most people have forgotten half of theirs.
2. Copy your instructions into a plain text file you own. The instruction text is the real asset — it is the part that survives every product change.
3. Press Migrate to plugin when the button appears — and test the result. Do not assume the migration worked; run your usual prompts and compare the answers with the old GPT.
4. Rebuild any custom action, or drop it. If the GPT called your own API, plan the rebuild now; it will not come across by itself.
5. Build new things as skills, plugins, or Projects — never as a new custom GPT. The old container is closing.

Also watch the file limits on the Gemini side: a Skill has a strict 100 MB total file limit, rejects old .doc and .xls files, compressed archives, audio, video, and GitHub files — and if your Gem is over the limit, Google deletes your largest files first.

The bigger lesson

AI features come and go fast. Plugins replaced GPTs before GPTs had replaced plugins, back in 2024. The durable asset was never the product — it is the instruction text itself, saved as a plain file you own. Keep a folder of your assistant recipes as text, and no retirement date can take them from you.

Paragon's verdict: 🟡 Watching

The retirement is real, dated, and confirmed by OpenAI's own help pages — that part is settled. The replacement is real too, but new and unproven for ordinary users: plugins and skills have not yet shown they are as easy as GPTs were. So migrate early, keep a copy of your instructions, and do not build anything new on Custom GPTs.

Sources: OpenAI Help Center, "Custom GPT retirement and migration FAQ"; OpenAI ChatGPT release notes, September 11, 2026; Google Gemini Apps Help, "About the transition from Gems to skills". Watch the video version on the Paragon AI MAG YouTube channel, and hear the full deep-dive conversation in today's Paragon AI MAG podcast episode.