ChatGPT is the primary interface most people use. It handles writing, research, coding help, summarizing documents, answering questions, generating images, analyzing data files, and supporting day-to-day productivity tasks. It is conversational and flexible — you describe what you need and it responds in natural language.

The free tier gives access to a current GPT-5-class model with some usage limits (and ads in the US). The $8/month Go plan and $20/month Plus plan raise those limits and add priority access to new features, while higher Pro tiers ($100–$200/month) unlock the most capacity. Team and Enterprise plans add shared workspaces, admin controls, and higher-volume access suitable for organizations.

Custom GPTs are pre-configured assistants built on top of ChatGPT. You define a name, persona, instructions, and optional tools — web browsing, code execution, file analysis — and the assistant follows that configuration every time it is used. You can build one for customer-facing support, internal documentation, onboarding guides, or specialized team workflows.

Custom GPTs are available to Plus, Team, and Enterprise users. They can be shared privately within an organization or published to the GPT Store. They are one of the fastest ways to deploy a specialized AI assistant without writing any code at all.

The OpenAI API gives developers direct access to the underlying models — the GPT-5 family and dedicated reasoning models — to build AI into their own products and workflows. Rather than using the ChatGPT interface, API users write code that calls the model directly and handles the output programmatically inside their own application or pipeline.

This is how most AI-powered products are built. An application calls the API with a prompt, receives a structured response, and uses that output inside its own interface or automated workflow. The API is priced by token usage rather than a flat monthly subscription.

The Assistants API and Agents SDK represent the most advanced layer, where AI is not just answering questions but executing multi-step tasks. An agent can use tools — search the web, run code, read files, call external APIs, manage memory — and loop through steps until a goal is reached. It can operate far more autonomously than a basic chat assistant.

OpenAI’s Agents SDK is designed for builders creating workflows where the AI needs to take action, not just generate text. This is the current frontier: not a conversation, but a working, goal-driven process that runs with minimal human input.

• ChatGPT free or Plus — everyday writing, research, summarizing, coding help, and Q&A
• Custom GPTs — repeatable tasks, internal tools, onboarding guides, or customer-facing assistants
• Team or Enterprise — shared workspaces, privacy controls, and admin features for organizations
• API access — developers building AI directly into products, automations, or data pipelines
• Assistants / Agents SDK — complex multi-step workflows that need to take action, not just respond

• A content marketer uses ChatGPT Plus to draft blog posts, edit copy, and repurpose content across formats in minutes
• A small business owner builds a Custom GPT to answer common customer questions using their own product knowledge base
• A software development team uses the API to add AI-powered features directly into their own application
• An operations manager uses an agent workflow to pull data from multiple sources, analyze it, and draft a weekly summary automatically
• A freelance analyst uploads spreadsheets and PDFs into ChatGPT to extract trends and generate chart-ready summaries without writing code

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