If you built a custom GPT so you'd stop re-explaining how you like things done, or so the people around you would stop asking you, there is a date to plan around: OpenAI says custom GPTs are scheduled to retire on 11 December 2026.

Before you decide where your instructions go next, it helps to know what each company says is changing, and who their instructions will reach afterwards. We read their own help pages on 26 October 2026 and link each one below. These pages change often, so check the link before you plan around a date.

What OpenAI says is changing

From OpenAI's Custom GPT retirement and migration FAQ:

The dates. "Custom GPTs are scheduled to retire on Dec 11, 2026." For affected Enterprise workspaces with an approved deferral, the date is 11 February 2027.
Your instructions. "Under the planned migration workflow, the GPT's instructions become a skill within the new plugin." Knowledge files are copied into the plugin's reference files. Custom actions don't transfer.
The people who used it. Migration "doesn't carry over your GPT's sharing settings or give its existing users access to the replacement", and a migrated personal plugin starts private.
Your conversations. OpenAI says existing conversations with custom GPTs remain accessible after retirement, while the GPTs and their GPT pages become inaccessible at the retirement date.

And from OpenAI's Plugins in ChatGPT: "Users on Business and Enterprise workspaces can share plugins with other members of their workspace."

It isn't only GPTs

Google. "Skills will replace Gems in 2027," says Google's page on the transition from Gems to skills (last updated 22 October 2026). Gems move to Settings in the Gemini app on 17 November 2026. For business and enterprise editions, no sooner than 1 March 2027, people can no longer create, edit or use Gems, and remaining Gems become draft skills. Google says a Gem's Drive permissions and sharing settings carry over to its skill, and that skills use the open, Markdown-based SKILL.md format.

Anthropic. Claude's organisation instructions (page dated 31 August 2026) are for Team and Enterprise plans. Owners set them, up to 3,000 characters, and they apply to everyone in the organisation; only Owners and above can view or edit them. A skill a colleague shares with you updates when its owner saves a new version, and "access is removed automatically if the recipient leaves the organization."

Organisation-wide instructions in ChatGPT. In an OpenAI community thread asking for instructions that apply to every chat in a ChatGPT Business workspace, OpenAI Support replied on 8 September 2026: "No timeline to share yet." It was still the latest reply on 26 October 2026.

A standard, partly. The Model Context Protocol, the open protocol JustOnce uses, has a Skills extension that lets an app discover skills and read their instructions, and its specification is marked Final. The community-maintained support table lists ChatGPT's support for it as Partial.

The pattern

Each of these lives inside one company's product. Some reach only one workspace or organisation. Others reach further but stay inside that product: ChatGPT shared projects can be shared on every plan, Free included, and a shared Gem's sharing settings carry over to its skill.

If everyone you need already uses the same product, its own sharing may be all you need. A JustOnce space is for rules kept with your own memory and documents rather than inside one assistant's project: each rule credited and versioned, and picked up by each member's own Claude today.

Where a JustOnce space fits

JustOnce is a memory and document store for your AI agent. A space is the part of it you share with the people you choose, invited by email whether or not they have an account yet, and house rules are that space's standing instructions and key facts.

Owners and editors write a space's rules and key facts. Each member's own Claude picks them up when a new chat starts, credited — "Set by Sam (Owner) · 3 Oct 2026".
Rules are guidance for that space's matters, never permission: they can't share, forget, invite or upload anything for anyone.
Every member sees who set each rule and when, and can turn a space's rules off for themselves.
A key fact is what a member wrote — JustOnce doesn't check it.
Viewers can read the rules; only owners and editors can change them.

Claude's organisation instructions reach your Claude organisation. A JustOnce space reaches the people you invite, in Claude today. Members join free; owning a shared space comes with Plus (one shared space) or Pro (three). When your assistant asks to share something or invite someone, nothing is shared or sent until you approve it in JustOnce.

House rules reach each member's own Claude today, and we'll add another assistant only after it passes its own live test. Your own memory and documents connect to more assistants; the dated list shows which.

Before 11 December

Write down what your GPT knows. OpenAI suggests reviewing a GPT's instructions, reference files and connected apps, and saving a few familiar prompts so you can compare the replacement's results.
Check who relies on it. Sharing settings don't carry over, so, as OpenAI advises, confirm that the people who use your GPT can open the replacement before you ask them to switch.
Sort your instructions by who they're for. Instructions for a task you run yourself can live in the plugin. Standing rules for the people around you, such as your partner, your family, or the people who help at home or in the business, can live in a shared space as house rules.
Keep each rule short. One instruction to a line is easier to read, credit and change than a pasted page. Never put codes or passwords in a space.