GPT-5.1

Model Overview

GPT-5.1 is an advanced AI model developed by OpenAI, belonging to the GPT-5.1 family. Released around late 2025 (with metadata indicating updates in July 2026), it is designed as a highly capable model for reasoning and agentic tasks. As of July 2026, the GPT-5.1 series is considered a predecessor to newer iterations like the GPT-5.6 series, but it remains a powerhouse with configurable reasoning effort. This model operates primarily via API, offering developers fine-grained control over computational "thinking" time based on query complexity.

Capabilities

• Adaptive Reasoning: Dynamically allocates reasoning or "thinking" time according to the prompt's difficulty. Supported levels include "none", "low", "medium", and "high".
• Massive Context Window: Capable of processing up to 400,000 tokens in a single context window, allowing for extensive document analysis and long-running context retention.
• Customization: Features multiple personality presets (e.g., Professional, Friendly, Candid, Quirky) enabling precise steering of the model's tone.
• Instruction Following: Delivers improved consistency and accuracy in adhering to complex system prompts and multi-step instructions compared to earlier models.

Example Use Cases

• Complex Problem Solving: Mathematical reasoning, logic puzzles, and deep analytical tasks where adaptive reasoning provides a significant advantage.
• Long-Form Document Analysis: Processing entire books, extensive legal contracts, or large datasets due to its 400k context window.
• Agentic Workflows: Acting as the core intelligence engine for autonomous agents that require deep planning and multi-step execution.

Performance & Benchmarks

While exact parameter counts remain proprietary (Unknown), GPT-5.1 demonstrated state-of-the-art performance at its release. It notably bridged the gap between rapid conversational responsiveness and deep, methodical reasoning. Base pricing was introduced at roughly $1.25 per 1M input tokens and $10.00 per 1M output tokens.

Intended Use & Limitations

• Intended Use: Designed for developers building robust applications that require both broad knowledge and deep reasoning capabilities via API.
• Limitations: As a legacy model (superseded by the GPT-5.6 family), users seeking the absolute latest state-of-the-art performance or the most cost-efficient inference should consider newer alternatives like GPT-5.6 Sol or Terra. The model operates exclusively on text modalities in its base API form.

About OpenAI

OpenAI is an artificial intelligence research laboratory consisting of the for-profit corporation OpenAI LP and its parent company, the non-profit OpenAI Inc. Known for developing the GPT series of large language models, OpenAI's mission is to ensure that artificial general intelligence (AGI) benefits all of humanity.