From Hope: 

The Tech 4 E4 builds on our 25+ years’ experience designing and manufacturing hydraulic brake systems. The Tech 4 uses all new internal sealing for reduced friction and the pivot spins on roller bearings, allowing the spring rate to be reduced. The lower spring rate in turn gives a lighter lever action, reducing rider fatigue and keeping our legendary feel and modulation.

The updated E4 caliper utilizes hybrid style Stainless steel pistons with a phenolic insert allowing for smoother movement and less maintenance, while still able to manage high temperatures without heat transfer during extreme use.

// Increased power versus Tech 3
// Lever shape updated to provide a more ergonomic shape orientated to provide the best mechanical advantage during braking.
// Hinged clamp reducing weight and ergonomics
// Shifter integration improved for more adjustability
// Tool free bite point and reach adjustments
// Hybrid piston design
// Rigid CNC'd one piece caliper
// Compatible with a wider range of current shifter options
// Complete brake available in Black or Silver with colour accent options of; Black, silver, purple, red, blue, or orange.
//Choose either standard or braided hose (braided hose is an extra cost)
// 30% pressure increase compared with the Tech 3 brake
// Hinged clamp design to reduce weight and reservoir area increased to lower overall stack height.
// Shifter integration has been improved and now offers 30° of angle adjustment as well as neater packaging and compatibility with the latest shifters. Lateral adjustment on both sides of the master cylinder is also possible to give a wide range of lever position options.
// Hybrid-style pistons that allow smoother movement and require less maintenance, and a phenolic insert to manage heat transfer during extreme use.
// The Tech 4 retains the tool-free bite point and reach adjustments from the Tech 3
// Tech 4 brakes are supplied with new racing compound pads.