Can I use custom GPT instructions in Claude?

Not directly. Claude does not read ChatGPT custom GPT configurations. You can copy the instruction text into a Claude Project or a Claude system prompt. Storing instructions in fenbs lets any connected assistant read them without manual copying.

Is there a free alternative to custom GPTs?

Most AI apps offer some form of reusable instruction setting on free plans. Claude.ai has a limited free tier with Projects. Gemini skills are available on Google's free plan. System prompts via API require a paid API account. fenbs has a free plan for one person.

Do Claude Projects have knowledge files like custom GPTs?

Yes. Claude Projects let you upload files to a project that the assistant can reference in all conversations within that project.

What happens to my custom GPT instructions when I switch to Claude?

They stay in ChatGPT. If you want to use the same instructions in Claude, copy them into a Claude Project or a fenbs Skill that Claude can read via MCP.

Which option is best for a small team that uses multiple AI tools?

fenbs is designed for this case: one shared record of instructions, decisions, and context that any connected AI app reads. It does not replace individual app configurations, but it gives every assistant the same starting point.

Custom GPT Alternatives for Reusable AI Workflows

Custom GPTs are one way to build a reusable AI assistant, but they are not the only one. Here is how Claude Projects, Gemini skills, system prompts, and other options compare on instructions, tools, and portability.

October 13, 2026Updated October 21, 20264 min read

A custom GPT is a saved ChatGPT configuration: a name, standing instructions, optional knowledge files, and a set of capabilities. It is useful, but it only works inside ChatGPT, and it ties your prompts and knowledge to one platform. Several alternatives let you build a reusable assistant with different trade-offs on portability, capability, and cost.

Whatever platform you use, the prompts and rules behind a good assistant are worth keeping in a portable place. fenbs stores your Skills and project rules in one record that Claude, ChatGPT, Cursor, Codex CLI, and Gemini CLI can all read via MCP, so the work does not start over when you switch tools.

What custom GPTs do well

Custom GPTs are good for sharing a configured assistant with a team or the public without sharing the raw instructions. You can publish to the GPT Store or share a link, and recipients get a usable assistant without seeing what is behind it. They also support knowledge file uploads, so you can give the assistant access to specific reference material the base model does not have.

Their limits: they only run inside ChatGPT, they cannot maintain memory of previous sessions (unless you connect an external memory action), and they are tied to OpenAI's plan structure. OpenAI has announced changes to custom GPTs; check their help center (opens in a new tab) for the current status.

Comparison of reusable assistant options

Reusable AI assistant options compared
Option	Works in	Knowledge files	Shareable	Portable prompts	Best for
Custom GPT	ChatGPT only	Yes	Yes (link or Store)	No	Sharing a configured assistant publicly or across a team on ChatGPT
Claude Projects	Claude.ai only	Yes (project files)	Team members only	No	A team working primarily in Claude.ai with shared instructions and files
Gemini skills (formerly Gems)	Google Gemini only	No (as of writing)	No	No	Personal reusable personas inside Gemini
System prompt (API)	Any model via API	No (bring your own)	Requires code	Yes	Developers building products where the instruction set is part of the app
Cursor rules	Cursor only	Via codebase	Repo-level	Partial	Coding assistants inside the Cursor editor
fenbs Skills	Any connected app via MCP	Not file uploads, but project context	Any team member with access	Yes	Teams using multiple AI apps who need prompts and context in one portable place

Claude Projects

Claude Projects let you set standing instructions and upload reference files that apply to every conversation inside that project. They also added shared memory on September 17, 2026, so the project can carry context between sessions. Projects are for you and the people you invite, not for public sharing.

If your team primarily works in Claude.ai and needs a shared assistant with persistent context, Claude Projects may serve you better than a custom GPT. For a detailed comparison, see Claude Projects vs. custom GPTs.

Gemini skills

Gemini skills (called Gems until they were renamed) let you save a reusable persona or instruction set inside Google Gemini. As of writing, they do not support knowledge file uploads, so they work best for instruction-based configuration rather than reference material. Gemini skills are scoped to your personal Google account and are not shareable.

Check Google's Gemini documentation (opens in a new tab) for the current feature set, as capabilities change frequently.

System prompts

A system prompt is an instruction set sent to a model at the start of every API call. Any model that accepts a system prompt can use one: GPT-4o, Claude, Gemini, Llama, and others. System prompts are the most portable option, but they require you to manage the delivery: you pass the prompt in code, not through a UI.

For developers, system prompts offer the most control. For non-technical users, they require a wrapper application to be practical.

Editor rule files

Coding editors like Cursor and Devin Desktop (formerly Windsurf) support project-level rule files that shape how the assistant behaves in that codebase. These are useful for coding tasks but are scoped to the editor and the repository. They do not transfer to ChatGPT, Claude, or other general-purpose AI apps.

How fenbs helps

Keep your prompts portable across AI apps

In fenbs, save your instruction sets as Skills and your project rules as Decisions and rules. Claude, ChatGPT, Cursor, Codex CLI, and Gemini CLI can all read them via MCP. When you switch platforms, the work stays. Create a free account to start building a portable prompt library today.

Create a free account

Free for one person · No credit card · Works with Claude, ChatGPT, Cursor and more

Who should pick which

You share the assistant with people outside your team or with the public: use a custom GPT with a Store listing or shared link.
Your team works primarily in Claude.ai and needs persistent context: use Claude Projects.
You build an app where the assistant is part of the product: use a system prompt delivered via the API.
You want the same prompts available in Claude, ChatGPT, and Cursor without rebuilding for each: store them in fenbs and connect your tools via MCP.
You only code and work entirely in one editor: use that editor's rule file system.

How to do this with fenbs

Create a free account and add a project for the work your assistant supports.
Add each instruction set as a Skill in fenbs, with a short note on the task it covers.
Connect the AI apps you use via MCP at /integrations: Claude, ChatGPT, Cursor, Codex CLI, and others.
When an AI session starts, it reads your Skills and project context from fenbs automatically.
When you change an instruction, update the Skill once in fenbs. All connected apps see the update.

For a deeper look at specific alternatives, see ChatGPT Projects vs. custom GPTs or explore Mem0 alternatives and Supermemory alternatives for AI memory tools.