9 questions answered. Every answer sourced.
The OpenAI API: A Practical Getting-Started Guide
The OpenAI API lets you use OpenAI's models inside your own apps and scripts. It is billed separately from ChatGPT. Here is how to make your first call and keep costs under control.
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Facts checked against official announcements and documentation, October 2026 · Last updated October 2026
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01 · Start
Getting started
Your first call takes a few minutes.
How do I get an OpenAI API key?
Create one in the OpenAI API dashboard and store it securely. OpenAI's quickstart suggests exporting it as the OPENAI_API_KEY environment variable rather than putting it in your code.
Source: OpenAI API: Developer quickstart
How do I make my first OpenAI API call?
Install the official SDK, create a client, and call the Responses API with a model and an input, for example model gpt-6-astra with a short text prompt. The SDK reads your key from OPENAI_API_KEY.
Source: OpenAI API: Developer quickstart
Is the OpenAI API the same as ChatGPT Plus?
No. ChatGPT plans cover the ChatGPT apps; the API is a separate developer service billed per token. A ChatGPT subscription does not include API credits.
Source: OpenAI API: Pricing
02 · Models
Choosing a model and managing cost
Picking the right tier saves more money than any other optimisation.
Which OpenAI model should I use in the API?
GPT-6.1 Sol for most agentic and professional tasks, GPT-6 Astra when you need the best result on hard problems, and GPT-6 Luna for high-volume, simple tasks.
Source: OpenAI: Introducing GPT-6.1 Sol; OpenAI: GPT-6 Astra, a new generation of intelligence; OpenAI API: Pricing
How much does the OpenAI API cost?
Per million tokens: GPT-6 Astra $10 input and $50 output; GPT-6.1 Sol $2 and $10; GPT-6 Luna $0.10 and $0.50. Cached input is much cheaper, Batch and Flex cost half, and priority processing costs more.
Source: OpenAI API: Pricing
How can I reduce OpenAI API costs?
Use the cheapest model that meets your quality bar, reuse prompts so cached input pricing applies, use Batch for work that does not need an immediate response, and cap output length.
Source: OpenAI API: Pricing; OpenAI: Introducing GPT-6.1 Sol
03 · Safety
Keeping your key and app safe
Most API mistakes are about key handling.
How do I keep my OpenAI API key safe?
Never put it in front-end code or a public repository. Store it in environment variables on your server, rotate it if exposed, and use separate projects and keys for different apps.
Source: OpenAI API: Developer quickstart
Why am I getting a 429 error?
A 429 means you hit a rate or quota limit, not that the model is unavailable. Slow down requests, add retries with backoff, or check your usage limits and billing.
Do I need to know how to code to use the API?
Basic coding helps. If you want AI features without code, ChatGPT, Codex or a no-code builder may be a better fit.
Sources
Read and checked October 2026. Policies change, so confirm anything time-sensitive on the source page.