What OpenAI says
OpenAI's migration guide says: "Custom actions do not transfer through the migration workflow." You rebuild them with a supported connector or a custom MCP server (Moving your custom GPT workflows to plugins). Its page on replacing an action says: "Before migrating, save the action schema, authentication method, and non-secret connection settings" (Replacing a GPT custom action). The same page tells you to leave "credentials, secrets, and hidden instructions" out of anything you hand to another model.
Where each part is
OpenAI's editor changes now and then, so the names may differ in yours. In the GPT editor:
- Open My GPTs, choose the GPT, click Edit, and go to Configure.
- Scroll to Actions and open the action.
- Schema. Select everything in the Schema box and paste it into a text file named after the action. It is an OpenAPI description: the server address, each operation and what it takes and returns.
- Authentication. Write down the type (none, API key or OAuth) and, for an API key, how it is sent, for example the name of the header. Do not write the key.
- Connection settings. Note the privacy policy address and any address the schema points at that your rebuild will need.
- When it is called. Copy the part of your instructions that says when the GPT should use the action, and one test prompt that makes it run.
What stays out of the file
API keys, OAuth client secrets, tokens and passwords inside an address. A schema can carry an example key by accident, so read it before you save it. Keep the real key in a password manager, next to your note of which header carries it.
A case from the OpenAI forum
On 4 October 2026 a user wrote that their email-manager GPT had an action calling a Make webhook, authenticated by an API key in a custom header. After the migration, "The Custom Action did not migrate. The migrated Beacon Plugin retained its instructions and Knowledge, but lost the external capability required for its core function." They rebuilt the tool as an MCP toolbox in Make, and then could not get the plugin to authenticate to it (Custom GPT to Plugin migration removed critical Action integration (October 4, 2026)). The thread had no reply when we read it. With the schema, the header name and the test prompt saved, a rebuild starts from notes and not from memory.
Rebuilding it
OpenAI points to a supported connector or a custom MCP server (Moving your custom GPT workflows to plugins). Which of those your plan can add varies: OpenAI's guide is written for ChatGPT Enterprise and says other plans may differ. We cannot promise a no-code route.
Keep it in the backup
In Skillcase, paste each action's schema into the Actions box. It reads JSON or YAML, lists the operations it finds, warns if something that looks like a key or token is in it, and saves the action in the backup with notes for the rebuild. It runs in your browser and uploads nothing.
Pack your GPT before December 11
Paste your GPT's setup, add its knowledge files and your ChatGPT export, and download a backup you can open anywhere, a skill for Claude, Gemini and ChatGPT, and your chats as Markdown. Free, in your browser, and nothing is uploaded.
Questions
Do custom GPT actions move to a plugin?
No. OpenAI says custom actions do not transfer through the migration workflow. Rebuild them with a supported connector or a custom MCP server.
What should I save from a GPT action before migrating?
OpenAI names three things: the action schema, the authentication method and the non-secret connection settings. We add the part of your instructions that says when to call the action.
Is it safe to paste an action schema into Skillcase?
Skillcase runs in your browser and uploads nothing. Leave API keys, tokens and secrets out. It warns when something in the schema looks like one.
Can I still copy the schema after I migrate?
OpenAI says the original GPT becomes read-only and stays usable until it retires. We found no statement on whether its Actions panel can still be opened, so copy the schema before you migrate.
Sources: OpenAI: Moving your custom GPT workflows to plugins; OpenAI: Replacing a GPT custom action; OpenAI Developer Community: Custom GPT to Plugin migration removed critical Action integration (October 4, 2026). Last checked: October 28, 2026. Skillcase is an independent tool by Peak Apps Studio and is not affiliated with OpenAI, Anthropic, Google or Ollama.