GPT-5.5 Instant: OpenAI Quietly Made This Your ChatGPT Default. Here's What Actually Changed.

On May 5, 2026, OpenAI replaced GPT-5.3 Instant with GPT-5.5 Instant as ChatGPT's default for all users — no announcement, no warning. It scores 88.7% on SWE-Bench, claims a 52.5% hallucination reduction, and costs $5/$30 per million tokens. Here's the honest breakdown, including the fine print OpenAI didn't lead with.