Your Digital Best Friend is Here: Mastering the New, Warmer GPT-5.1!

I. Unpacking the Dual Brains of GPT-5.1

The GPT-5.1 family is structured around two main models, designed to balance speed and deep thought:

1. GPT-5.1 Instant: Speed Meets Empathy

GPT-5.1 Instant is the default workhorse model in ChatGPT. This is where the biggest personality changes in GPT-5.1 reside, aiming for a more conversational and potentially "playful" style.

• Adaptive Reasoning: For the first time, GPT-5.1 Instant incorporates adaptive reasoning. This means the GPT-5.1 model will decide when to "think before responding" to tricky questions, leading to more accurate answers for complex tasks, while remaining quick for easy ones. This adaptive reasoning capability helps GPT-5.1 perform significantly better on benchmarks like AIME 2025 (mathematics) and Codeforces (coding).
• Instruction-Following: GPT-5.1 Instant boasts systematically improved instruction adherence, meaning it is much more likely to strictly follow specific user commands (like limiting all replies to exactly six words).
• API Access: The GPT-5.1 Instant model is accessible via the API as gpt-5.1-chat-latest.

2. GPT-5.1 Thinking: The Efficient Expert

GPT-5.1 Thinking is the advanced model focused on complex reasoning and long-chain tasks. The improvements here are largely engineering-focused.

• Smarter Thinking Time: GPT-5.1 Thinking balances speed and computational effort better than its predecessor. For simple tasks (like summarization), the thinking time is shortened (up to twice as fast as GPT-5 Thinking's quickest tasks). For highly complex tasks (like large-scale code refactoring), the GPT-5.1 model deliberately spends more time "chewing" on the problem to deliver a more complete solution.
• Clarity and Detail: Answers from GPT-5.1 Thinking are designed to be clearer and less reliant on jargon, offering more human-readable explanations.
• API Access: The GPT-5.1 Thinking model is accessible via the API as gpt-5.1.

II. GPT-5.1 User Guide: How to Personalize Your AI (Tutorial)

One of the most exciting aspects of GPT-5.1 is the completely revamped "Personality Tuning Bench," allowing you to customize your AI partner with far greater precision.

Step 1: Accessing GPT-5.1

1. Web Interface: The front end of ChatGPT defaults to GPT-5.1 Auto. The system will automatically switch between GPT-5.1 Instant (for quick chats) and GPT-5.1 Thinking (for analysis or complex queries) based on your prompt. You can also manually switch to GPT-5.1 Instant or GPT-5.1 Thinking in the model selector.
2. Rollout: GPT-5.1 models are rolling out first to paid subscribers (Pro, Plus, Go, Business, Enterprise, and Edu), followed by free users. Legacy GPT-5 models will be available in a dropdown for three months for those needing a transition period.

Step 2: Customizing the GPT-5.1 Personality

GPT-5.1 offers powerful new ways to dictate tone and style.

1. Choose a Preset Style: You can select from eight unique chat styles, including Friendly, Professional, Candid, Quirky, and Efficient (the former "Robot" style). Choosing these presets immediately adjusts the tone for your GPT-5.1 conversations.
2. Fine-Tuning Sliders: The personalization settings now include fine-grained controls via sliders. You can adjust:
   • How Concise (brief) the output should be.
   • How Warm (friendly) the model's tone is.
   • The frequency of Emoji Use.
3. Real-Time Updates: A major improvement in GPT-5.1 is that personalization settings and custom instructions now apply instantly to all your chats, including ongoing conversations. Furthermore, the system may actively suggest updating your global style based on cues within your dialogue (e.g., if you frequently ask it to "be less verbose").

III. The GPT-5.1 Coding Powerhouse: Codex

For developers, the GPT-5.1 launch includes two specialized coding models:

1. GPT-5.1-Codex

GPT-5.1-Codex is specifically optimized for software engineering workflows.

• Enhanced Performance: GPT-5.1-Codex showed moderate but important gains on coding benchmarks, scoring 76.3% on SWE-bench (up from 72.8% for GPT-5).
• Agentic Workflows: This GPT-5.1 variant supports complex, agentic tasks, including large-scale refactoring and code review. It is designed to be highly "steerable" and strictly adhere to developer instructions, producing cleaner code than the base GPT-5.1 model.
• New Tools: GPT-5.1 introduces new developer tools, such as apply_patch, which allows the model to change code, create, edit, or delete files, enabling deeper automation.
• Adaptive Reasoning in Code: Developers can adjust the reasoning effort using the reasoning.effort parameter, allowing the GPT-5.1-Codex model to dynamically adapt its computation based on task complexity.
• Pricing: The API pricing for GPT-5.1-Codex is listed as $1.25 per 1M input tokens and $10 per 1M output tokens.

2. GPT-5.1-Codex-Mini

The GPT-5.1-Codex-Mini is a compact, cost-effective variant. It is optimized for resource-constrained environments (like education or startups), but maintains near state-of-the-art performance, multimodal intelligence, and the same tool access as GPT-5.1-Codex. The API pricing for GPT-5.1-Codex-Mini is significantly lower at $0.25 per 1M input tokens and $2.00 per 1M output tokens.