The one thing to understand first
A Custom GPT, a Claude Project, and a Gemini Gem are all the same idea: a saved prompt plus some reference files. That is the whole thing. It answers when a person opens it and types. It does not run on a schedule, watch your inbox, or do anything by itself.
The moment you catch yourself saying "I want it to do this every morning" or "every time a customer emails," you have outgrown this category. That is real automation, and it is the rest of the Wiring phase (start with the first five automations).
How the three compare
All figures change often. Confirm on the vendor's own page before you rely on them.
| Custom GPT (OpenAI) | Claude Project (Anthropic) | Gemini Gem (Google) | |
|---|---|---|---|
| Cost to build | Paid plan only (around $20/mo) | Free tier works (max 5) | Free |
| Can do more than chat? | Yes: browse, make images, run data analysis, call other tools | Knowledge plus Claude's built-in tools | Knowledge plus live Google Drive |
| Knowledge files | 20 files, large | About 200K words; more on paid | 10 files |
| Share with your team | Link, store, or workspace | Team plan only (around $30/seat) | Like sharing a Google Doc |
| Live-updating knowledge | No | No | Yes, via Google Drive |
Build your first one in five steps
Works the same on any of the three:
- 1Take your best saved prompt and split it in two: the instructions (who this assistant is, how it answers) and the knowledge (reference docs it should rely on).
- 2Open the builder, give it a clear name, paste the instructions.
- 3Upload one to three of your most-used files: a price sheet, an SOP, a brand-voice doc.
- 4Test it with three to five questions you would actually ask. Fix the instructions until the answers are right.
- 5Decide who can use it.
The privacy rule that matters for client work
On the free and personal tiers, all three may use the documents you upload to improve their models unless you turn that off. On the business and team tiers, that is off by default.
Do not put client records or anything with personal information into a free personal assistant. If the assistant needs real client data, use a business or team tier.
Which one to pick
- Gemini Gem if you want the lowest barrier. It is free to build, lives in Google Workspace, and can read live from Google Drive so it never goes stale.
- Custom GPT if you want the most capable single assistant and your team already lives in ChatGPT. You will need a paid seat to build.
- Claude Project if the work is heavy on long documents, writing, and analysis. Note that sharing with your team needs the paid Team plan.
Do not agonize over lock-in. The instructions are just text. You can rebuild the same assistant on another platform in minutes.