You need the internet to play games online on your Xbox One, but most Xbox One games don't necessarily require an internet connection.
How to play your digital Xbox games offline
Yes, you can: How to play Xbox 360 games on Xbox One – GeekWire
Microsoft Says If You Don't Have Internet: Get Xbox 360, Not Xbox One
New Xbox App (Beta) on Mobile Keeps You Connected to Your Games, Friends, and Fun - Xbox Wire
How to Set Up Xbox Game Streaming, Play Games on Your Phone
How to Set Up Xbox Game Streaming for Your Phone
Can You Play Xbox Games On Microsoft Surface?
Everything You Need To Know About Xbox Play Anywhere Program - MSPoweruser
Xbox players can now chat and play online for free — but there's a catch