ChatGPT 5: What’s New and How It Works

Published on October 21, 2025

OpenAI launched GPT-5 on August 7, 2025, and rolled it into ChatGPT with smarter reasoning and a new routing system that chooses the right mode for your task. If you’ve seen the note “Used GPT-5” under some replies, that’s ChatGPT automatically picking the GPT-5 family when it helps most.

Key Changes at a Glance

  • Two modes, one picker: ChatGPT can run Chat or Thinking for GPT-5, and Auto decides when to think longer for complex work.
  • Better reasoning & memory: GPT-5 improves multi-step reasoning and long-context handling, especially in projects and multi-turn workflows.
  • Responses API: Devs get stateful-by-default conversations, hosted tools, and easier agentic flows—this is how apps tap GPT-5’s strengths.
  • Capacity updates: Plus/Enterprise plans gained higher weekly limits and options to force Thinking or keep it fast.

How the Modes Work

  • Auto: Let ChatGPT choose between speed and depth. It switches to GPT-5 Thinking when your request needs more deliberate reasoning.
  • Thinking: You can explicitly select deeper reasoning for analysis, planning, coding, or debugging.
  • Fast/Instant (where available): Prioritizes quick replies using lighter GPT-5 variants.

You may sometimes see a banner like “Used GPT-5”. That’s ChatGPT’s router picking GPT-5 (or GPT-5 Thinking) for the best result in that turn.

What Developers Get

If you build with OpenAI, the Responses API brings persistent tool state, cleaner multi-modal calls, and smoother agent workflows—designed with GPT-5 in mind. This reduces boilerplate and keeps conversation/tool context around without extra plumbing.

Why It Matters

  • Users: Smarter default answers with fewer toggles to manage; you can still force modes for control.
  • Teams: Enterprise tiers offer higher message capacity and admin controls while retaining GPT-5 quality.
  • Builders: The API shift means faster iteration on assistants that reason, search, code, and use tools.

Quick Tips

  • For research or complex planning, switch to Thinking if Auto isn’t deep enough.
  • For speed or casual chat, stick to Fast/Instant (when offered in your plan).
  • In apps, adopt Responses API to unlock GPT-5’s stateful workflows with less code.

Ready To Jumpstart Your Business?

Frequently Asked Questions

What is ChatGPT 5, exactly?

It’s ChatGPT running on OpenAI’s GPT-5 family. ChatGPT can route between GPT-5 Chat and GPT-5 Thinking depending on task complexity.

What does the 'Used GPT-5' label mean?

ChatGPT’s router chose GPT-5 (often the Thinking variant) for that specific reply to be more helpful on complex or sensitive topics.

Do I have to pick Thinking mode myself?

Not necessarily. Auto mode decides when to think longer, but you can manually choose Thinking for deep analysis or planning.

What’s the Responses API and why should I care?

For developers, Responses makes GPT-5 stateful by default and streamlines tool use (file search, code, image, etc.), enabling more capable agent workflows with less code.

Are there new limits or plans tied to GPT-5?

Yes. OpenAI updated message limits for Plus and offers higher or effectively unlimited capacity on Business/Enterprise tiers for certain GPT-5 variants, subject to policy.

Sources

↑