Guide
Microsoft Copilot agents vs custom GPTs
A Microsoft 365 Copilot agent and a ChatGPT custom GPT start from the same two things: instructions and knowledge. The differences are where they live and what's next. A Copilot agent lives in Microsoft 365, can draw on SharePoint, your work content and Copilot connectors depending on licence, and is shared with people as owners or chat users. A custom GPT lives in ChatGPT, and OpenAI retires custom GPTs on 11 December 2026, replacing them with plugins inside ChatGPT. If your documents and people are in Microsoft 365, a Copilot agent is the natural home; if your team works in ChatGPT, move the GPT to a plugin or take its instructions out as a skill.
Short answer
- Same core: instructions and knowledge.
- Copilot agent: Microsoft 365 knowledge, by licence; shared as owners or chat users.
- Custom GPT: retires 11 December 2026.
- Choose by where your documents and people already are.
Side by side
| Copilot agent (Agent Builder) | Custom GPT | |
|---|---|---|
| You set | Name (30 characters), description (1,000), instructions (8,000), knowledge, starter prompts | Instructions and knowledge files |
| Knowledge | Web for everyone; SharePoint, files and connectors with pay-as-you-go or a Copilot licence; email and Teams with the licence | Files you upload |
| Sharing | Private until shared; Can edit or Can chat; chat link; org-wide toggle an admin can restrict | After the move, the replacement plugin starts private |
| Actions | Copy the agent to Copilot Studio | Don't transfer; rebuild with a connector or a custom MCP server |
| What's next | Current | Retires 11 December 2026; plugins replace it |
From Microsoft Learn pages updated in September and October 2026 and OpenAI's custom GPT retirement FAQ (search-result text), read 5 November 2026. The custom GPT column describes the product OpenAI is retiring.
A worked example: three GPTs, three homes
Illustration: a made-up business. A 30-person consulting firm runs on Microsoft 365, with Copilot licences for 10 people. It has three custom GPTs to move before December. The operations lead agrees two criteria with the partners before deciding each one: where the knowledge lives (weight 60) and who needs it (40).
- Proposal writer, drawing on past proposals in SharePoint, used by 10 licensed consultants: a Copilot agent, with the SharePoint folder as knowledge.
- Onboarding helper, used by everyone, drawing on the public handbook site: a Copilot agent grounded on that site, which Copilot Chat users can use without a licence.
- Client research assistant, used by two partners who work in ChatGPT: its instructions move to a plugin in ChatGPT, and a copy goes into the firm's skill library.
Each line marks what came only from a vendor's page as unverified until the team tests it on a real task.
How to decide
- List each custom GPT, who uses it and what knowledge it needs.
- Check where that knowledge lives: SharePoint and Teams point to Copilot.
- Check licences: web and instructions for everyone; work data needs pay-as-you-go or a Copilot licence.
- Plan sharing: owners as Can edit, everyone else Can chat.
- Move before 11 December 2026; see custom GPTs end on 11 December.
Skills for this
- Operations and adminVendor comparison with weighted scoresCompares 2-5 vendors on weighted criteria you agree first: must-haves, evidence-based scores, total cost, risks, and one recommendation.
- AI practiceTurn a prompt into a skillTurns a prompt that works into a skill the whole team can reuse, with a valid name, a when-to-use description, steps, an output template, an example, and checks.
- AI practiceContext brief for an AI assistantWrites instructions for an AI assistant or agent: role, audience, can and can't, sources of truth, tools, format, examples, edge cases, and handoff.
Questions
What is the difference between a Copilot agent and a custom GPT?
Both are an assistant built from instructions and knowledge. A Copilot agent lives in Microsoft 365 and can draw on SharePoint, your work content and Copilot connectors, depending on licence; a custom GPT lives in ChatGPT, and OpenAI retires custom GPTs on 11 December 2026, replacing them with plugins inside ChatGPT.
Do Copilot agents need a Microsoft 365 Copilot licence?
Not for every agent. Microsoft's docs say Copilot Chat users can use agents grounded on instructions or the web. Agents grounded on SharePoint, connectors or embedded files need pay-as-you-go billing in the tenant or a Microsoft 365 Copilot licence, and email, people and Teams knowledge need the licence.
Can I share a Copilot agent with my team?
Yes. An agent is private until you share it. You can add people as Can edit (owners) or Can chat, add groups as chat users, copy a chat link, or turn on org-wide sharing, which an admin can restrict.
AI skill
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Sources
- Microsoft Learn: Build agents in Agent Builder (updated 27 October 2026) — name up to 30 characters, description up to 1,000, instructions up to 8,000; knowledge from public websites, organizational and personal work content, embedded files and Copilot connectors, availability by licence; code interpreter and image generator; skills can be added; actions need Copilot Studio (read 2026-11-05)
- Microsoft Learn: Share and manage agents built in Agent Builder — private until shared; Can edit (owners) and Can chat; groups only as chat users; chat link; org-wide sharing toggle, which admins can restrict; org catalog after admin approval (read 2026-11-05)
- Microsoft Learn: Agent capabilities and licensing models — Copilot Chat users get agents grounded on instructions or the web; SharePoint, connectors and embedded files need pay-as-you-go billing or a Microsoft 365 Copilot licence; email, people and Teams knowledge need the licence (read 2026-11-05)
- OpenAI Help: Custom GPT retirement and migration FAQ — custom GPTs retire on 11 December 2026; instructions become a skill in a plugin, which starts private; custom actions don't transfer; read through search-result text (read 2026-11-05)