It is every bit as powerful as the larger brother, with Snapdragon 800 processor and the same 20 MP camera with Sony G Lens that gives other cameraphones a run for their money. The only thing that was scaled down was the screen resolution from Full HD to HD, but given the much smaller screen diagonal, you still have plenty of pixel density to work with...
Source: http://www.phonearena.com/news/Sony-Xperia-Z1S-leaks-out-mini-version-of-the-Z1-for-the-global-market_id48495
Source: http://www.phonearena.com/news/Sony-Xperia-Z1S-leaks-out-mini-version-of-the-Z1-for-the-global-market_id48495