GPT-5.5 Instant

// Overview

GPT-5.5 Instant is OpenAI's fast, low-latency model that became ChatGPT's default for all users on May 5, 2026, replacing GPT-5.3 Instant. It was the everyday workhorse of the GPT Instant line — the model most people talked to in ChatGPT — tuned for quick, conversational replies without the extended deliberation of OpenAI's separate thinking models. OpenAI summarized the release as 'smarter, clearer, and more personalized.'

On August 6, 2026 OpenAI retired GPT-5.5 Instant from that role. Its GPT-5.6 August update states plainly that the newly released August versions of GPT-5.6 Sol and GPT-5.6 Luna 'will replace GPT-5.5 Instant': Free and Go users moved to GPT-5.6 Luna as the new everyday default, while Plus and Pro users moved to an updated GPT-5.6 Sol with a slider that controls how much effort ChatGPT spends on a response. OpenAI reported that both replacements cut factual error rates substantially versus GPT-5.5 Instant — roughly 60% across all three of its hallucination prompt sets for Sol, and over 60% on high-stakes prompts for Luna.

Compared with GPT-5.3 Instant, the headline improvement is factuality: OpenAI reported that GPT-5.5 Instant produces 52.5% fewer hallucinated claims on high-stakes prompts covering medicine, law, and finance, while keeping the same instant response latency. It also posts large jumps on hard reasoning and multimodal evaluations — 81.2 on AIME 2025 (up from 65.4) and 76 on the MMMU-Pro multimodal reasoning benchmark (up from 69.2).

GPT-5.5 Instant accepts text and image input and returns text. It adds deeper personalization: with memory enabled it can refer back to your past conversations, uploaded files, and (when connected) Gmail to give more tailored answers, and a new 'memory sources' view shows which stored context shaped each response so you can edit or remove individual entries. For developers, OpenAI exposes the model through the API as the chat-latest alias rather than a pinned snapshot, so apps on chat-latest track the current default. As a member of the GPT-5.5 family it carries the same 1,050,000-token context window, up to 128,000 output tokens, and a December 1, 2025 knowledge cutoff.

// Benchmarks

This model's scores

1. AIME 2025 (math)81.2%
2. MMMU-Pro (multimodal reasoning)76%
3. Hallucination reduction vs GPT-5.3 Instant (high-stakes prompts)52.5%
4. HealthBench (length-adjusted)51.4%
5. HealthBench Hard (length-adjusted)22.9%

Scores on a 0–100 scale (25-point gridlines); higher is better. Each benchmark links to its published source.

// Pricing

GPT-5.5 family rate; Instant is served via the chat-latest alias with no separate Instant tier.

Pricing source ↗

// Strengths

• Much lower hallucination rate than GPT-5.3 Instant on high-stakes medical, legal, and financial prompts
• Instant, low-latency responses for everyday chat — no extended reasoning wait
• Strong multimodal reasoning over images and charts (MMMU-Pro 76)
• Built-in personalization from past conversations, files, and connected Gmail
• Very large 1,050,000-token context window for long documents and threads

// Best for

• Everyday ChatGPT conversation, drafting, and quick Q&A
• Higher-trust questions in medicine, law, and finance where factuality matters
• Image and chart understanding alongside text
• Personalized assistance grounded in your own history, files, and email
• Latency-sensitive chat apps that call the chat-latest API endpoint

// How to access

// GPT Instant — every version

The full lineage of the GPT Instant line, newest first. Every version has its own page — click any to compare specs, benchmarks and pricing.