GPT-5.5 Instant was officially released on May 5, 2026, as the new default model for ChatGPT worldwide. It replaces GPT-5.3 Instant, providing a smarter, more personalised experience for both free and paid users.

Key Improvements & Features

• Reduced Hallucination: OpenAI claims the model significantly cuts down on incorrect information, particularly in high-stakes fields like law, medicine, and finance.
• Token Efficiency: While more expensive per token, it is more "token-efficient," using 30.2% fewer words and 29.2% fewer lines to complete the same tasks compared to previous versions.
• Enhanced Context & Personalization: The model can now pull context more effectively from past conversations, uploaded files, and connected Gmail accounts to provide tailored suggestions.
• Benchmarking Success: It achieved a score of 81.2 in the AIME 2025 math test (up from 65.4 in GPT-5.3) and outperformed its predecessors in multimodal reasoning.
• Knowledge Cutoff: The model's training data includes information up to August 2025.

The Wider GPT-5.5 Ecosystem 

The "Instant" release follows the launch of the more powerful GPT-5.5 Thinking and GPT-5.5 Pro on April 23, 2026.

• GPT-5.5 Thinking: Designed for complex, multi-step agentic work, including advanced coding and scientific research.
• GPT-5.5 Pro: Aimed at enterprise users, offering extended reasoning and expert-level accuracy for professional workflows.