GPT-5.1 is here: what the new generation of ChatGPT means for users and developers

In mid-November, OpenAI officially introduced GPT-5.1, a new version of the model that powers ChatGPT. The goal of this release is to address the main criticisms of GPT-5 – above all to make conversations “warmer”, more natural, and better at following user instructions.

The biggest change is that the entire GPT-5 line now revolves around two main modes: GPT-5.1 Instant and GPT-5.1 Thinking. Instant is designed for fast, everyday tasks, while Thinking kicks in for deeper, more complex analysis when it’s really needed.

For everyday users this means more natural dialogue and less of a “robotic” tone. For developers it means a more stable API, adaptive reasoning, and a new tool for working with code.

Illustration of the GPT-5.1 model processing user requests

What exactly is GPT-5.1 and how is it different from GPT-5?

GPT-5.1 is an evolution of the existing GPT-5 model, not a completely new architecture built from scratch. OpenAI describes it as a “smarter and more conversational” upgrade that mainly:

  • follows complex instructions more reliably
  • produces clearer answers with less jargon
  • adjusts how long it “thinks” depending on how difficult the task is (adaptive reasoning)

In practice, GPT-5.1 Instant is the default model in ChatGPT Plus accounts, while Thinking is activated when more advanced, multi-step reasoning is needed (long essays, serious code analysis, complex planning). For free accounts, the rollout of 5.1 still depends on OpenAI’s roadmap, so some users may still see older models.

Instant vs Thinking: two modes instead of one

The new series revolves around two core modes:

GPT-5.1 Instant

  • focused on speed – answers arrive very quickly
  • uses “lightweight” adaptive reasoning: it doesn’t waste time on deep analysis for simple questions
  • ideal for everyday chat, translation, text summarization, basic code questions

GPT-5.1 Thinking

  • meant for hard problems: multi-step reasoning, complex requests, advanced data analysis
  • dynamically decides how long it needs to “think” – it solves simple tasks quickly, but allocates more compute time for complex ones
  • produces multi-step explanations with arguments and a clear structure

If you use ChatGPT via the web or mobile interface, the system will usually automatically decide whether to rely more on Instant or Thinking, depending on what you asked. In the API world, developers can explicitly choose which model they want to call.

A new “personality” for ChatGPT: presets, tone, and style

One of the main complaints about GPT-5 was that it felt “flat” and overly serious. GPT-5.1 addresses this by introducing:

  • improved personality presets (e.g. Default, Professional, Friendly, Quirky, Nerdy, Cynical…)
  • the ability for users to tune the tone in settings (formal/informal), amount of humor, answer length, and more
  • a warmer, less “official” style of conversation, especially in Instant mode

In other words, ChatGPT now feels less like “a PDF in chat form” and more like a conversational partner you can tune to your liking: whether you want a teacher, an IT buddy, or an ultra-concise assistant that doesn’t waste words.

What does it bring to developers: adaptive reasoning, apply_patch, and a shell tool

For developers using the OpenAI API, GPT-5.1 introduces several serious upgrades:

1. Adaptive reasoning

Instead of every request consuming the same amount of “thinking steps”, GPT-5.1 can:

  • respond quickly to trivial tasks
  • automatically invest more compute when the task requires deeper reasoning

That means lower average latency and more efficient use of resources, especially in apps that call the API thousands of times per day.

2. apply_patch – a tool for painless code edits

The new apply_patch tool allows the model to:

  • add, modify, or delete files in a project
  • create patches without manual copy-pasting of diffs
  • perform refactors more reliably because it has a better view of the whole codebase

This is especially interesting for AI assistants in IDEs, GitHub Copilot–style tools, and similar workflows where the model can propose and apply changes on its own.

3. Shell tool

The second major addition is a shell tool – the model can propose and run command-line commands, inspect the output, and adjust its next steps based on the result. This is an important step toward “agent” scenarios where AI doesn’t just write code, but also runs it, tests it, and debugs it.

How will this affect users?

For everyday users, GPT-5.1 means:

  • more natural conversations, with fewer “dry” phrases
  • more control over tone – whether you want a formal advisor, a relaxed friend, or an ultra-efficient bot
  • better handling of long and complex questions

For developers, GPT-5.1 makes it easier to:

  • build complex AI assistants (IDE helpers, agents, backend services for analysis, recommendations, interpretations…)
  • reduce the risk of “silly” bugs in code, thanks to more stable refactoring
  • connect GPT-5.1 to existing dev tools (Copilot, CLI, editors) more seamlessly

Conclusion

GPT-5.1 is not a “magical leap” like the jump from GPT-3 to GPT-4, but it is a very substantial upgrade to the GPT-5 series: warmer conversations, smarter reasoning, and serious new tools for developers.

The combination of Instant + Thinking, personality presets, and API improvements makes a clear difference compared to the previous generation – both for people who just want to “talk to an AI”, and for teams building real products on top of it.

If you use ChatGPT every day or build your own AI services, GPT-5.1 is essentially the new default you’ll want to factor into your plans for 2026.