Apple has overhauled Siri with an artificial intelligence "brain transplant" using proprietary, on-device large language models under Apple Intelligence, enabling cross-app data synthesis, drafting complex communications, and executing multi-step workflows. The upgraded Siri relies on an on-device neural engine with approximately 3 billion parameters, ensuring sensitive data like health records and private messages never leaves the iPhone for routine tasks, while complex requests route to Private Cloud Compute servers. This localized processing is vital for regions like Kenya and Nigeria due to high mobile data costs. Prerequisites include iPhone 15 Pro, iPhone 16 series, or an M1/M2/M3/M4 iPad or Mac, with software requirement iOS 18.2 or later. Users must speak conversationally, as legacy syntax like "Siri, search the web for..." will fail. Step 1 involves contextual email summarization: the prompt "Siri, summarize this email thread and draft a professional reply agreeing to the Thursday meeting, but noting that I need the Q3 budget attached" causes Siri to parse the email chain, extract scheduling details, and generate a draft for review in the Mail app. Step 2 enables cross-app data synthesis, bridging separate applications without manual copy-pasting.