GPT-5.1: Smarter, more natural, and conversational like a real human

OpenAI has officially announced GPT-5.1, the latest evolution in the GPT-5 family that brings its intelligence, logical reasoning, and conversational capabilities closer to human-like. The new release includes two upgraded models, GPT 5.1 Instant and GPT 5.1 Thinking, which are designed to increase both the speed and depth of interactions, and feature warmer, more natural-sounding voices.

GPT-5.1 Instant: Faster, warmer, and more adaptable 

GPT 5.1 Instant is the model most frequently used by ChatGPT users, and this new version is designed to be friendlier, funnier, and smarter, with conversations that are both natural and accurate.

First, adaptive reasoning, which allows the model to “think before answering” in some complex cases, to arrive at more accurate answers without sacrificing the speed of answering common questions.

In internal testing, GPT 5.1 Instant shows significant improvements in math and coding, outscoring previous models in AIME 2025 and Codeforces tests.

GPT-5.1 Thinking: Smarter in reasoning and more clearly explaining 

GPT 5.1 Thinking is designed for deep reasoning and complex problem solving. It dynamically adjusts its “thinking” time, taking longer for difficult questions and answering immediately for easy questions.

One of the key features of this model is its “clarity of answers.” The model uses simple language, reduces unnecessary technical jargon, and avoids complex language. This makes it ideal for academic work, technical writing, or enterprise use cases.

Additionally, GPT 5.1 Thinking's tone is more empathetic and approachable, ideal for users who require emotional interactions or situations that require subtle understanding.

Smarter personality and tone customization 

OpenAI understands that users want their AI to “talk more like themselves,” and GPT 5.1 makes that easier.

You can choose from 6 new improved tones: 

• Default – Balanced and natural 
• Friendly – Fun, friendly and conversational. 
• Efficient – Concise and to the point 
• Professional – Formal and elegant 
• Candid – Casual and straightforward 
• Quirky – Creative and unique 

Users can further customize the tone of the conversation, such as warmth, conciseness, use of emoji, or speed reading capabilities. ChatGPT can also suggest automatic tone adjustments during a conversation if it detects a change in tone.

GPT-5.1 Auto: Intelligent model selection system 

The new GPT 5.1 Auto feature automatically selects the most appropriate model (Instant or Thinking) based on the complexity of the task, meaning users no longer have to manually switch models — everything is handled intelligently and quickly.

In the coming days, GPT 5.1 Instant and GPT 5.1 Thinking will be available to Pro, Plus, Go, and Business users before expanding to general users. Enterprise and EDU users will get early access before the full release.

Developer Access (API Access) 

Both GPT 5.1 Instant and GPT 5.1 Thinking will be available via the OpenAI API this week.

• GPT 5.1 Instant → gpt 5.1-chat-latest 
• GPT 5.1 Thinking → gpt 5.1 (with adaptive reasoning feature) 

Developers can experiment with contextual reasoning features to build more responsive, intelligent, and flexible applications. 

Why GPT 5.1 matters 

The release of GPT 5.1 marks a significant step forward for AI, which understands human context and emotions better. It not only enhances logical reasoning capabilities, but also creates conversational experiences that are more natural and “human” than ever before.

What's next? 

GPT 5.1 is just the beginning of a new era of AI capabilities. OpenAI aims to develop it in three main directions:

• Smarter reasoning — Gives the model a deeper understanding of the context. 
• More natural communication — Gives the model a deeper understanding of the context. 
• การปรับแต่งที่ดียิ่งขึ้น — Allow users to customize the AI ​​to best suit their own style. 

With GPT 5.1 becoming the primary model in both ChatGPT and the API, users will experience the most powerful, fun, and “human” conversations yet — like a personal assistant that truly understands you.