I'll google it for you......yes the sd300 is the newer thinner cable used with the 12s di2 groups.

i'm looking this cable to update the DI2 shifters firmware, after the firmware is upgraded the cable is not needed anymore ?

The ew-300 cable is only used on the newer 12 speed systems. Those systems have a Bluetooth system built into the rear derailleur that uses the Shimano app to upgrade the firmware. You use the Shimano e-tube app on your cell phone. The older systems use a special interface adapter that you have to purchase to do that. Short answer is that you never need that cable to do a firmware upgrade.

Shimano Ew-Sd300 E-Tube Di2 Wire

Product ID: 417640649

Details

Brand
SHIMANO
Color
Black
Global Trade Identification Number
Item Length
150
Item Weight
1.44 ounces
Manufacturer
Shimano

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Details

Brand
SHIMANO
Color
Black
Global Trade Identification Number

Description

Shimano Ew-Sd300 E-Tube Di2 Wire

Specifications

ASIN	B08X1YSN8L
Best Sellers Rank	#42,807 in Sports & Outdoors ( See Top 100 in Sports & Outdoors ) #14 in Bike Cables
Brand Name	SHIMANO
Color	Black
Customer Reviews	4.8 4.8 out of 5 stars (121)
Global Trade Identification Number	00192790635286
Included Components	Cables & Extensions, E-Tubes
Item Length	150 Millimeters
Item Weight	1.44 ounces
Manufacturer	Shimano
Manufacturer Warranty Description	Limited Warranty
Material Type	Multi
UPC	192790635286
Unit Count	1.0 Count

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