Anthropic's internal codename for Claude Sonnet 5 is "Fennec." A fennec fox is known for massive ears relative to its body size. Sonnet 5 reportedly has a 1M token context window — five times larger than Opus 4.5's 200K. The codename is the spec sheet. Previous Claude models all used animal codenames. The leak came from misconfigured Vertex AI deployment logs on Google's infrastructure, where the model already exists. It's just waiting to be switched on.