Custom AI Assistants: GPTs, Gems, and Skills — The Definitive Guide to Choosing Right

How many times have you opened ChatGPT, Gemini, or Claude and had to start from scratch — explaining who you are, what you do, and how you want it to talk to you? It’s exhausting. Like showing up to your own office every morning and introducing yourself to your own team.

That’s exactly why the major AI platforms created custom AI assistants: versions trained with your instructions, your context, and your files, ready to work the way you need them to from the very first message. ChatGPT calls them GPTs, Google Gemini calls them Gems, and Claude calls them Skills (or Projects).

In this guide, you’ll learn exactly what they are, how they work, how they differ — and most importantly, which one is right for your business, your team, and your goals.

What Are Custom AI Assistants — and What Can They Do?

A custom AI assistant is a configured version of a language model that you give permanent instructions, reference files, and a specific role. Instead of starting every conversation cold, the assistant already knows who you are, how you work, and what you expect from it.

Think of it this way: if the standard ChatGPT is a new hire on day one, a custom GPT is that same person three months in — they know the business, the company’s tone, the key clients, and the internal processes.

These assistants can take on very specific roles:

• Content writing in your brand’s voice and style.
• Document analysis based on your own criteria.
• Customer support using your company’s language and knowledge base.
• Market research focused on the sectors you care about.
• Report generation in a pre-defined format.

The difference between using generic AI and using a custom assistant is the same as the difference between hiring a freelancer on the fly and having a full-time team member who already knows the business inside and out.

ChatGPT GPTs: The Largest Ecosystem on the Market

OpenAI’s Custom GPTs were the first to arrive, launched in November 2023, and they remain the most widely used worldwide.

How Do GPTs Work?

A custom GPT is built through the GPT Builder, a conversational interface where you describe what you want your assistant to do and OpenAI automatically drafts the initial instructions. You can also write instructions manually if you want more control.

The most powerful feature of GPTs is Actions: connections to external APIs that let your GPT query your CRM, update a database, send data to a webhook, or pull live information from any service with an OpenAPI specification. No other platform comes close to this in a native user interface.

How Many Files Can You Upload?

Up to 20 knowledge files with a combined storage limit of 512 MB per GPT — the most generous file storage of the three platforms.

How Much Does It Cost?

Starting at ChatGPT Plus ($20/month). Free-tier users can use published GPTs but can’t create their own.

The GPT Store: The App Store of AI

OpenAI built a public marketplace where any creator can publish their assistant and make it available to millions of users. If you want to build an AI product for a mass audience, this is your best stage.

When to Use GPTs

• When you need integrations with external tools (CRMs, APIs, databases).
• When you want to publish your assistant in a public marketplace.
• When you work across creative, analytical, and automation workflows.
• When the multimodal ecosystem (text, image, voice) matters to you.

Gemini Gems: The Perfect Fit for Google Workspace

Gems are Google Gemini’s version of custom AI assistants, officially launched in August 2024. Their standout differentiator isn’t raw technical power — it’s native integration with the Google ecosystem.

How Do Gems Work?

Creating a Gem is surprisingly fast: anywhere from 3 to 10 minutes. You write the behavioral instructions, upload up to 10 reference files, and you’re done. The interface is clean and intuitive, designed for users without a technical background.

What makes Gems special is that they can read your Gmail, Google Drive, and Google Calendar in real time. A Gem can analyze client emails, review proposals in Drive, or factor in your calendar for the day to give you relevant context. No other platform offers this level of integration without additional setup.

Looking ahead, Gems will also be able to write, create, and modify documents, events, and emails within Workspace — completing a full automation loop.

How Much Does It Cost to Create a Gem?

Here’s a meaningful advantage: anyone with a Google account can create Gems for free. Paid plans (Gemini Advanced, ~$20/month) unlock more powerful models and extended context.

When to Use Gems

• When your daily operation revolves around Google Workspace (Gmail, Drive, Calendar, Docs).
• When you want a fast, low-friction assistant with minimal setup.
• When the work is primarily internal and you don’t need to publish it anywhere.
• When Google business data integration is your top priority.

Keep in mind: Gems lose much of their competitive edge outside the Google ecosystem. If your company runs on Microsoft 365 or tools outside Workspace, this integration won’t add much value.

Claude Skills and Projects: The Deepest Architecture

Claude, developed by Anthropic, launched Skills in October 2025, building on an existing system of Projects (released in 2024). Together, they form the most sophisticated customization architecture of the three platforms.

How Do Claude Skills Work?

Skills are Markdown-based instruction files (SKILL.md) that tell Claude exactly how to handle specific categories of tasks. You can write extremely detailed instructions — with no character limit — and Claude follows them consistently whenever the situation calls for it.

There are four types of Skills:

1. Anthropic-native Skills: for document creation (Word, Excel, PowerPoint, PDF). Available to all users.
2. Public Skills: created and shared by the community.
3. User Skills: custom-built for your own workflows.
4. Enterprise Skills: configured by teams within Team or Enterprise plans.

Claude Projects complement Skills: they’re persistent workspaces with custom instructions and reference documents that maintain context over time. For teams working with sensitive content or requiring high editorial voice consistency, the combination of Project + Skills + Claude Styles is the most powerful setup on the market.

How Much Does It Cost?

Skills are available on Free, Pro, Max, Team, and Enterprise plans. Some require code execution to be enabled in your account settings.

When to Use Claude Skills and Projects

• When you need highly detailed instructions and consistent behavior over time.
• When you work with critical content — legal, compliance, or high editorial standards.
• When your team needs an assistant that holds brand voice with precision.
• When data privacy is non-negotiable (Anthropic does not use your data to train its models by default).
• When you’re doing deep analysis, long-form writing, or complex intellectual workflows.

Side-by-Side Comparison: GPTs vs. Gems vs. Claude Skills

Common Mistakes When Using Custom AI Assistants

Mistake #1: Confusing quantity with a system

Building 20 GPTs doesn’t mean you have a productive AI system. It means you have 20 different entry points into the same chaos. Before creating assistants, define the specific problem each one is meant to solve.

Mistake #2: Vague or generic instructions

“Act like a marketing expert” is not a useful instruction. A solid instruction specifies the tone, the response format, the boundaries, the use cases, and examples of what you expect.

Mistake #3: Not updating your knowledge files

An assistant trained on two-year-old information will give outdated answers. Schedule periodic reviews of the reference documents you upload.

Mistake #4: Choosing a platform based on hype instead of context

If your business lives inside Google Workspace, a Gem will save you hours of setup. If you need integrations with your CRM or a custom system, GPTs with Actions are the better choice. The right platform isn’t the most popular one — it’s the one that fits how you actually work.

How to Choose the Right AI Assistant for Your Business

Before building any assistant, answer these three questions:

1. Where does the information live that the assistant needs? In Google Drive and Gmail → Gem. In external APIs → GPT with Actions. In Word docs or PDFs you upload manually → any of the three.

2. Is the assistant for internal use or for distribution? Internal team use → Claude Projects or Gems. Distributing to external users → OpenAI’s GPT Store.

3. How much precision and consistency do you need? Fast, varied tasks → GPTs. Seamless Google integration → Gems. Maximum editorial, legal, or brand-voice precision → Claude Skills + Projects.

Frequently Asked Questions About AI Assistants

Conclusion: AI That Works the Way You Do

Custom AI assistants — GPTs, Gems, and Skills — represent the most significant shift since large language models first arrived: moving from talking to generic AI to working with a digital collaborator that already knows your business.

The choice between platforms isn’t about which AI is “the best.” It’s about fit. GPTs if you need integrations and mass distribution. Gems if your day-to-day runs on Google Workspace. Claude Skills if depth, privacy, and editorial quality are non-negotiable.

One thing is true across all three: whoever configures their AI assistants well today will have a real competitive edge in the years ahead. The technology is there. The difference will be made by those who know how to orchestrate it.

Do you already have a custom AI assistant set up for your business? If you’re not sure where to start, a quick audit of your workflows can reveal in 30 minutes which platform and use case has the highest potential for you.