A Custom GPT is a customized version of ChatGPT created with specific instructions, knowledge files, and tools. Created via the GPT Builder by ChatGPT Plus subscribers.
Custom GPTs let users package up a specific use case into a reusable, shareable assistant. Instead of repeatedly typing the same setup prompt ('You are a senior copywriter for B2B SaaS...'), the configuration is baked in. ChatGPT users can publish Custom GPTs to the GPT Store for others to discover and use. As of 2026, the GPT Store contains tens of thousands of community-built Custom GPTs.
A user creates a 'B2B Cold Email Coach' Custom GPT with system instructions defining the persona ('senior B2B SaaS copywriter who specializes in technical industries'), a knowledge file containing past successful emails as reference, and the web browsing tool enabled. Anyone using this GPT immediately gets that persona without copy-pasting setup prompts.
Compared to a saved prompt template: A Custom GPT is a fully-realized assistant with persistent context; a prompt template is a starting message you paste in. Both work; Custom GPTs are richer but locked to ChatGPT; prompt templates work across any AI tool. Compared to OpenAI's API + custom system prompt: Same underlying capability, but Custom GPTs are accessible without code; API integration requires development.