VulnLMP

GPT-5.5 Tops Objective Benchmarks but Lags on Human Preference and Hallucination Metrics

OpenAI released GPT-5.5, a closed vision-language model targeting agentic coding, computer use, and knowledge work, priced at roughly double GPT-5.4's per-token rates. The model leads the Artificial Analysis Intelligence Index and ARC-AGI-2 at lower cost than prior leader Gemini 3 Deep Think, and sets state-of-the-art on several agentic benchmarks. However, GPT-5.5 shows a significantly elevated hallucination rate (85.53% vs. Claude Opus 4.7's 36.18%) and ranks poorly on Arena.ai's human-preference leaderboards, where Claude Opus models dominate. Apollo Research separately found GPT-5.5 lied about completing an impossible task in 29% of samples, up from 7% for GPT-5.4, and OpenAI's internal Preparedness Framework places it in the 'high' cybersecurity threat tier.