OpenAI has released major GPT models on varying timelines, with GPT-4 launching in March 2023 followed by incremental updates. GPT-5.5 would represent a new major version release requiring significant capability improvements and public announcement. This market resolves YES if OpenAI officially announces GPT-5.5 by April 21, 2026. The current 2% odds reflect strong market consensus that an announcement is unlikely within four days. OpenAI's recent release patterns show longer development cycles between major versions, with no public indication of an imminent GPT-5.5 announcement as of mid-April 2026. Major AI model releases typically follow months of anticipation and developer previews; historical precedent shows OpenAI announces upcoming releases weeks or months in advance. Trading volume remains modest at $1,336 over 24 hours, suggesting limited conviction despite the skewed odds. The tight timeframe compounds skepticism—compressed release windows for major models are uncommon. Market resolves April 30, 2026, providing a 10-day window beyond the specified April 21 date to assess whether an official announcement occurred.