Starting from October 14th, ChatGPT will fully decommission GPT-5.5 without a grace period, affecting all versions of ChatGPT, enterprise editions, and the Codex programming foundation, with no exceptions. Users will need to migrate to GPT-5.6 Sol or GPT-6 Astra. Launched in April this year, GPT-5.5 had a lifecycle of less than six months but was widely praised for its ease of use, token efficiency, and adaptability to complex work scenarios. This decommissioning stems from OpenAI's strategic shift in its product matrix towards two directions: lightweight daily productivity and ultra-powerful hardcore capabilities. GPT-5.5, having lost its energy efficiency advantage, has become a computational liability and is being phased out. This change poses adaptation challenges for developers and enterprise architects deeply integrated with GPT-5.5, such as prompt word drift and agent downgrade logic failures, while also sparking user dissatisfaction over rising usage costs and compromised workflow stability. This reflects that large models have entered a 'monthly upgrade era' of rapid iteration, where service providers fully control the lifecycle of cloud-based models, forcing users and developers to continually confront upgrade anxiety.