AgentKit vs Assistants API vs GPTs: Which OpenAI tool should you use?

Trying to keep up with all the new tools OpenAI releases can feel like a full-time job. Just when you think you’ve got a handle on things, a new name pops up. You’ve probably seen AgentKit, the Assistants API, and custom GPTs thrown around, but let’s be honest, it’s not always obvious what they do, who they’re for, or which one you should actually use.

They're all impressive in their own way, but they're built for very different jobs. This guide is here to clear things up. We’ll walk through what makes each tool different, what it really takes to get them working, and when it makes more sense to skip the developer toolkit and go for a platform that’s ready for business right out of the box.

AgentKit vs Assistants API vs GPTs: A quick breakdown

Before we jump into a side-by-side comparison, let's get on the same page. Think of these tools as different ways to build something. One gives you a complete assembly kit with instructions, another hands you a powerful engine and says "good luck," and the last one is a simple gadget you can personalize a little.

What is OpenAI's AgentKit?

AgentKit is the newest and most complete package from OpenAI for building AI agents. It's basically a collection of tools meant to make life a bit easier for developers, covering everything from building the agent to getting it into an app. It has a few main parts:

• Agent Builder: A visual, drag-and-drop screen where you can map out your agent's logic and behavior.

• Connector Registry: A central spot to manage how your agent pulls in data or connects to other tools.

• ChatKit: A pre-made UI kit to help you put a customizable chat window on your website or in your app.

• Evals: A system to test and measure how well your agent is performing so you can make sure it’s reliable.

So, think of AgentKit as the full workshop. It bundles up some of the more technical tools into a friendlier package for developers and companies that want to build complex agents without starting entirely from scratch.

What is the Assistants API?

If AgentKit is the workshop, the Assistants API is the high-performance engine sitting in the middle of it. It’s a framework for developers to build AI assistants purely with code. It takes care of some of the really tough stuff, like remembering long conversations, calling other tools and APIs (a feature OpenAI calls Function Calling), and pulling information from files you give it.

This is a much more hands-on tool than AgentKit. It gives you all the flexibility and control you could want, but that freedom comes with a whole lot of complexity. You need serious coding skills and the ability to build and manage all the other pieces of the puzzle yourself.

What are custom GPTs?

Custom GPTs are by far the most straightforward of the three. They’re a simple, no-code way for anyone with a ChatGPT Plus subscription to create their own version of ChatGPT. You can give it a specific personality, feed it instructions, and upload documents for it to use as a knowledge base, all by just typing out what you want in plain English.

They're fantastic for personal projects or simple internal tools. The catch? They have some pretty big limitations for business use. GPTs can't leave the ChatGPT ecosystem, which means you can't put them on your website or properly integrate them with the software you use to run your business. They’re more of a fun, customizable gadget than a real business solution.

Who are AgentKit, the Assistants API, and GPTs for?

Now that you have a better idea of what these tools are, let's figure out who should be using them. The answer usually boils down to two things: your team's technical skills and what you're trying to get done.

AgentKit: For developers on a deadline

AgentKit is built for developers or teams who want to create and launch a custom AI agent without having to build every single component from the ground up. It’s a great fit if you're building a customer support agent or an internal tool for your team that needs to handle tasks with multiple steps. But even with its visual builder, you'll still need a developer to write code, manage the backend, and get it all deployed.

Assistants API: For developers who want total control

The Assistants API is for the seasoned developer who needs to weave AI logic deep into an application's backend. This is your go-to when AgentKit’s visual canvas feels too limiting or when you're automating a complicated workflow that doesn't even have a chat window. It gives you complete, fine-grained control over the agent's behavior but requires a deep understanding of how to build software.

GPTs: For individuals who need a quick, simple chatbot

GPTs are for pretty much everyone else. If you're not a developer and you just need a quick, custom chatbot for a simple job, this is where you start. You could create a helper to summarize your meeting notes, a guide to explain project documentation, or a fun bot to share with your friends. The name of the game here is speed and simplicity, not building a scalable business tool.

AgentKit vs Assistants API vs GPTs: A head-to-head comparison

Picking the right tool is all about matching its capabilities to your project's needs. And while OpenAI's tools are incredibly powerful for developers, they often miss the key features that businesses actually need, like easy help desk integrations, useful analytics, or a safe way to test the AI before it talks to customers.

Here’s a quick look at how they stack up:

Feature	AgentKit	Assistants API	Custom GPTs
Primary User	Developers	Backend Developers	Non-technical users
Ease of Use	Moderate (visual builder + code)	Difficult (code-only)	Easy (no-code)
UI Components	✅ Yes (via ChatKit)	❌ No (bring your own UI)	✅ Yes (ChatGPT UI)
Custom Integrations	✅ Yes (APIs, Connectors)	✅ Yes (via Function Calling)	⚠️ Limited (Actions)
Deployment	Self-hosted backend required	Self-hosted backend required	Hosted on ChatGPT
Multi-Agent Logic	Limited (handoffs)	Programmatic, but complex	❌ No
Business Analytics	❌ No (requires custom build)	❌ No (requires custom build)	❌ Basic usage stats
Use Case	Custom agentic applications	Backend AI automation	Simple, personal chatbots

The reality of AgentKit vs Assistants API vs GPTs: Setup, deployment, and maintenance

It's one thing to read a feature list, but it's another to understand what it actually takes to get these things running in the real world. The true cost goes way beyond the price on the website; it includes developer hours, server costs, and all the work required to keep it running smoothly.

The developer-heavy path of AgentKit and the Assistants API

Let's be real: even with AgentKit's nice visual builder, this is not a "no-code" solution. You still need a developer to handle the backend, set up and manage servers, and plug the chat UI into your product. And once it's live, the work is far from over. Someone has to manage API versions, watch for errors, and constantly tweak the agent to make sure it's not going off the rails.

For most companies, this turns into a multi-month project that needs dedicated engineers. This is exactly why platforms like eesel AI exist. Instead of a dev project, you get a self-serve tool with one-click integrations for help desks like Zendesk and Freshdesk. You can be up and running in minutes, not months.

The simplicity and constraints of GPTs

GPTs are incredibly easy to create, and that's their biggest selling point. But that simplicity comes at a cost for any real business use. They are completely stuck inside the ChatGPT interface. You can't put one on your website, you can't hook it up to your help desk, and you have virtually no control over security or data privacy. They're a great place to experiment, but they just aren't built for day-to-day business operations.

AgentKit vs Assistants API vs GPTs: How the pricing works

The way you pay for these tools is another huge factor, especially for businesses that need a predictable budget.

• AgentKit & Assistants API: Both are priced based on API usage, which means you pay for the number of tokens (pieces of words) you send and receive. This can lead to some surprisingly high and unpredictable bills, especially if your agent becomes popular.

• GPTs: To create or use a custom GPT, both you and your users need a paid ChatGPT Plus subscription.

For a business, a usage-based bill that can unexpectedly spike is a big risk. One busy week could blow your entire budget for the month. This is a major reason why platforms like eesel AI offer transparent plans based on capacity, not per-ticket fees. You get a flat, predictable cost that doesn't penalize you for growing.

The alternative: When you need an AI agent, not a dev project

While OpenAI gives you a fantastic set of building blocks, most support, IT, and operations teams don't want to start a massive software project. They just need something that solves their problem today.

That’s where a purpose-built platform comes in. Instead of giving you a box of parts, it gives you a finished product designed for what you need to do.

With eesel AI, that looks like this:

• Actually self-serve: You can sign up and launch a working AI agent in a few minutes without ever needing to talk to a salesperson.

• Connects to your knowledge: It instantly hooks into the places where your team's knowledge is already hiding, whether that's old help desk tickets, your Confluence space, or shared Google Docs. The AI has the right context from the very start.

• Test without risk: Before the AI ever talks to a real person, you can run it in a simulation mode on thousands of your past support tickets. This gives you a clear, data-driven report on how it will perform.

• You're in control: You get a no-code editor that lets you do much more than just answer questions. You can set up custom actions, fine-tune the AI's personality, and decide exactly which types of questions it should handle.

Making the right choice for your team

Choosing between AgentKit, the Assistants API, and GPTs really comes down to one question: are you looking to start a development project, or are you looking to solve a business problem?

OpenAI provides a powerful and flexible, but also very complex, toolkit for developers. For everyone else, a business-ready platform like eesel AI delivers the results you’re actually looking for, like automated support and instant answers for your team, without forcing you to build the whole thing yourself.