How to use the ChatGPT API: A complete guide from A to Z.

What is the ChatGPT API? Simply put, it's a "gateway" that allows you to integrate ChatGPT's intelligence into any of your applications, websites, or workflows – not just the chat interface on ChatGPT.com.

If the original article about the ChatGPT API on TipsMake.com was written when GPT-3.5 Turbo and GPT-4 were the newest models, by 2026, the picture has completely changed. OpenAI has launched many new models such as GPT-4o , GPT-4.1 , GPT-4.1 mini , and GPT-5,  each with different performance, costs, and capabilities. More importantly, the way users interact with the API has also changed significantly: instead of having to write Python code yourself, today you can connect the ChatGPT API to your daily work simply by dragging and dropping on platforms like n8n , Make.com , or Zapier – completely without needing any programming knowledge.

This article updates all content to reflect the realities of 2026: from how to obtain API keys and current models to practical integration guides for both those who know how to code and those who don't.

Understand the ChatGPT API correctly before you begin.

What are the differences between the ChatGPT API and regular ChatGPT?

When you go to chat.openai.com and ask ChatGPT a question, you are using OpenAI's "retail" product – a paid monthly plan with a pre-designed interface and message limits based on the plan.

The ChatGPT API is different: you pay based on the actual amount of data processed (calculated in tokens – roughly equivalent to "pieces of text," about 750 English words are worth 1,000 tokens). You have full control over integrating it into your own application and workflow, without being limited by the OpenAI interface.

When should you use an API instead of regular ChatGPT?

1. You want to automate a repetitive process (for example, automatically composing customer response emails every time a new order is placed).
2. You want to integrate AI into your software, website, or application.
3. You need ChatGPT to run in the background, without requiring someone to manually type it in.
4. You want to use AI as a "link" in an automated workflow.

Step-by-step guide to obtaining your ChatGPT API key.

This is a mandatory step before doing anything with the ChatGPT API, whether you're using code or drag-and-drop tools.

Step 1: Instructions on obtaining and setting up ChatGPT API Keys

Go to platform.openai.com and register an account. You can use your regular email, Google account, or Microsoft account for faster registration. Once you've logged in, select Create new secret key.

Important note for users in Vietnam: OpenAI Platform accounts (using APIs) are separate from regular ChatGPT accounts, even if they share the same email address. Please ensure you are logged in at platform.openai.com, not chat.openai.com.

Fill in your Secret Key information, including the name and project (if applicable). If not, just enter the name and select Create secret key.

After selecting "Create secret key," you will see the API Keys appear as shown in the image below. These will be your official API Keys. Select "Copy" and paste them into your notes application or any application or software where you can save this API Keys code.

Now, in the API Keys interface, you will see the number of API Keys you have created. Select the red trash can icon to delete the API Keys you no longer want to use.

Now go back to n8n, select the Open AI node > choose any request such as Generate an image. 

On this interface, you will see the Credential section first; select Set up credential or the pen icon as shown in the image below.

Paste the API Key you obtained following the instructions above into the API Key field, scroll down, and select Save. You're done!

Step 2: Add credit to your account.

OpenAI's API charges based on usage; there is no perpetual free plan. To get started, you need to go to Home > Add credits as shown below, or select Settings → Billing → Add payment method and add an international payment card (Visa/Mastercard supports international payments).

Select "add payment details" and fill in the information of the credit card you are using.

After adding the card, deposit a minimum of $5 to get started. This is enough to test with tens of thousands of questions using the mini-model.

Note for Vietnamese users: OpenAI's payment system uses Stripe and may reject some domestic bank cards. It is preferable to use Visa/Mastercard cards from major banks such as Vietcombank, Techcombank, VPBank, or international virtual cards.

Step 3: Protect your API key

Your API key is the "key" to accessing your account. If someone else obtains this key, they can use your quota and spend your money. Here are some basic security principles:

1. Never share your API key via chat, email, or any other channel.
2. Do not store the key directly in the code and upload it to GitHub/GitLab (use a .env file instead).
3. Do not buy "key shares" or "shared accounts" from unknown sources.
4. If you suspect your key has been compromised, go to API keys and click Revoke to disable it immediately, then generate a new key.

Current ChatGPT API models in 2026

This is the most important update compared to the original article. The GPT-3.5 Turbo and GPT-4 Turbo Preview models mentioned in the old article are outdated. OpenAI now offers the following models:

1. GPT-40 is a multimodal model (capable of processing text, images, and audio), offering faster speeds and 50% lower costs compared to the previous GPT-4. It is the most popular choice for most tasks.
2. GPT-4.1 - a newer generation model, handles longer contexts and is more accurate than GPT-4.0 in many complex tasks. Suitable for analyzing long documents or processing complex logic.
3. GPT-4.1 mini and GPT-40 mini are compact, very low-cost versions suitable for simple tasks such as classification, short summaries, and answering FAQs.
4. GPT-5 - the most powerful model currently available, but also the most expensive. It should only be used for tasks that truly demand the highest quality.

Practical advice: You don't necessarily need the most expensive model for everything. For most everyday automation tasks, the GPT-4o mini or GPT-4.1 mini is sufficient and offers significant cost savings.

Using ChatGPT API with Python code - for those who know how to program.

This section updates the content from the original article with the latest models and syntax as of 2026.

Install the library:

 pip install openai python-dotenv 

Create a .env file to securely store your API key.

 OPENAI_API_KEY="sk-." 

Here's an example of a basic API call using GPT-40:

 from openai import OpenAI from dotenv import load_dotenv load_dotenv ( ) client = OpenAI ( ) response = client . chat . completions . create ( model = "gpt-4o" , temperature = 0.7 , max_tokens = 1000 , messages = [ { "role" : "system" , "content" : "Bạn là trợ lý hỗ trợ khách hàng chuyên nghiệp." } , { "role" : "user" , "content" : "Sản phẩm của tôi bị lỗi, tôi cần làm gì?" } ] ) print ( response . choices [ 0 ] . message . content ) 

Important note when choosing a model: Replace "gpt-4o"it with "gpt-4.1-mini"or "gpt-4o-mini"for simple tasks to save significant costs. Detailed pricing is always available at openai.com/api/pricing .

Control costs when using ChatGPT API

This is the biggest concern for API newcomers. The good news is that it's completely controllable if you do it right.

Track your expenses: Go to platform.openai.com → Usage to see how many tokens you've used and your daily expenses. This page is updated in near real time.

Set a monthly limit: Go to Settings → Limits to set your monthly spending limit . When the limit is reached, the API will stop responding instead of continuing to charge you.

Choose the right model for the task:

1. Summary, classification, simple FAQ → use gpt-4o-miniorgpt-4.1-mini
2. Write content, analyze documents, and use them.gpt-4o
3. Complex arguments, lengthy documents, high quality requirements → use gpt-4.1orgpt-5

Use the Batch API if real-time processing isn't required: OpenAI offers a Batch API that allows you to send multiple scheduled processing requests (within 24 hours) at only 50% of the cost of a regular API call. This is suitable for tasks that don't require immediate results, such as processing large amounts of data overnight.

Frequently Asked Questions

Is the ChatGPT API free?

1. There are no perpetually free plans. OpenAI used to offer free credits upon new registration, but this policy has changed. Currently, you need to top up your credit with a prepaid plan to get started. The cost is very low if using the mini-model: around a few thousand Vietnamese dong for thousands of questions.

Are there differences between a standard ChatGPT API key and a Platform API key?

1. There is no such thing as a "standard ChatGPT API key" - the API key is always generated at platform.openai.com. You use this key to connect from any application or tool.

Can I use the ChatGPT API for commercial purposes?

1. Yes, OpenAI's terms allow the use of APIs in commercial products/services. However, please carefully read the usage policy at openai.com/policies/usage-policies to avoid violations.

Should I start with n8n, Make, or Zapier if I don't know how to code?

1. If you're a complete beginner, start with Zapier as it's the easiest and has many templates available. Once you're familiar with it, switch to Make for more customization options. If you want to self-host and don't want monthly fees, n8n is the best long-term option.

Conclude

The ChatGPT API is no longer just for programmers. By 2026, with the support of automation platforms like n8n, Make, and Zapier, anyone can connect the intelligence of GPT-40 or GPT-4.1 to their daily work—automating emails, processing data, writing content, or providing customer support—without writing a single line of code.

The key things to remember: obtain the API key correctly, set cost limits from the start, choose a model that suits your tasks, and begin with a small workflow before scaling. Once you get used to how it works, you'll realize that the ChatGPT API is one of the most powerful productivity tools you'll ever use.