GPT-5.5

GPT-5.5 (Generative Pre-trained Transformer 5.5) is a large language model (LLM) released by OpenAI on April 23, 2026. The model is also known by its codename "Spud". OpenAI reported GPT-5.5 benchmark scores including 82.7% on Terminal-Bench 2.0, 51.7% on FrontierMath Tier 1–3, and 35.4% on FrontierMath Tier 4, while listing lower scores for Claude Opus 4.7 and Gemini 3.1 Pro on the same benchmarks. OpenAI said a recurring tendency in its models to mention goblins, gremlins, and other creatures began with GPT-5.1 and became noticeable in GPT-5.5's Codex testing. The company attributed the behavior to rewards used when training the "Nerdy" personality, which favored creature-word outputs and transferred beyond that personality during later training. OpenAI said it retired the Nerdy personality, removed the goblin-affine reward signal, filtered training data containing creature words, and added a developer-prompt instruction for GPT-5.5 in Codex. In April 2026, a GPT-5.5 developer-prompt instruction in the GitHub repository of Codex told it not to mention goblins if the user prompt did not require it. GPT-5.5-Cyber, along with Codex Security, was being used in June 2026 at the launch of the Patch the Planet project to help open-source projects find and fix vulnerabilities.