this is probably the first ESC that supports the new firmware BLHeli_S. 

Specifications:
Continuous Current: 30A
Burst Current: 40A
Input Voltage: 2S-4S LiPO
Weight: 5.5g with wires and heat shrink wrap
Dimensions: 25x13mm





In terms of firmware, compared to the the previous version of BLHeli:

• BLHeli_S has good Sync holding properties even not better
  
• you cannot switched off damped light.
  
• BLHeli_S has motor PWM that is Synchronous to the MCU master clock, as it is generated by hardware. This makes the motor Silent.
  
• BLHeli_S has very Small throttle Steps. The resolution varies between hardware configurations (MCU clock speed and driver type), and is between a nominal 512 steps and 2048 steps.
  
• BLHeli_S supports very high motor Speeds. A BB1 MCU will support 350k erpm, and the limit of the BB2 is not yet known, so the code is set to limit at 500k erpm.
  
• BLHeli_S supports regular 1-2ms input signal, as well as Oneshot125, Oneshot42 and Multishot. Autodetected when the ESC sees an input signal
  
• configuration and setting up is the same as regular BLHeli ESC, you can program the ESC through FC
  

http://www.rcgroups.com/forums/showthread.php?t=2640796