Is this compatible for 8 speed?

Not perfectly - the m3100 model is really meant for 9 speed

Will this replace the stx rc on a Trek 7300 8 speed?

Shimano's Compatibility charts won't show this "9-speed" derailleur as compatible with 8-speed components, but it should work just fine. Shimano 8-speed shifters will work. This RD can handle larger cogs than were common in the 8-speed era, up to 36t largest cog, but assuming you have 11-32 it'll work. I have an stx rc RD on one of my bikes, and wouldn't hesitate to try this as a replacement.

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Shimano,Black,ERDM3100SGS Alivio Alivio M3100 Rear derailleur, 9-Speed, Shadow Design, SGS Long cage

Product ID: 241101188

Details

Brand
SHIMANO
Color
Black
Item Weight
0.2 Kilograms
Material
other
Mounting Type
Braze-On Mount

🔧SGS long cage for smooth chain management

⚙️9-speed precision shifting

🛡️Shadow RD tech for derailleur protection

$78.59

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Description

🚴‍♂️ Shift into the future with Shimano’s stealthy precision!

TRUSTED PERFORMANCE - Backed by Shimano’s 2-year warranty and top-tier customer ratings (4.6/5).
LIGHTWEIGHT ROBUST - Steel and aluminum build balances strength with minimal weight at just 0.2 kg.
TRAIL READY DURABILITY - Shadow RD design minimizes damage from trail obstacles, keeping your ride smooth and worry-free.
OPTIMIZED CHAIN CONTROL - SGS long cage design prevents chain drops and enhances drivetrain stability.
SEAMLESS 9 SPEED SHIFTING - HyperGlide system ensures crisp, reliable gear changes for every terrain.

The Shimano Alivio M3100 SGS rear derailleur features advanced Shadow RD technology and a long cage design to deliver durable, smooth 9-speed shifting. Engineered with steel and aluminum, it offers lightweight strength and optimized chain management, making it ideal for trail and trekking cyclists seeking reliable performance backed by a 2-year warranty.

Specifications

ASIN	B08CGYD213
Best Sellers Rank	#35,779 in Sports & Outdoors ( See Top 100 in Sports & Outdoors ) #11 in Rear Bike Derailleurs
Brand	SHIMANO
Brand Name	SHIMANO
Case Material Type	Steel & Aluminum
Color	Black
Customer Reviews	4.6 out of 5 stars 687 Reviews
Global Trade Identification Number	04550170621155
Included Components	Bike Parts
Item Dimensions L x W x H	6.69"L x 4.43"W x 3.94"H
Item Type Name	Rear derailleur.
Item Weight	0.2 Kilograms
Manufacturer	Shimano
Manufacturer Part Number	ERDM3100SGS
Material	other
Material Type	other
Model Number	C8C086
Mount Type	Braze-On Mount
Mounting Type	Braze-On Mount
Number of Teeth	36
Product Dimensions	6.69"L x 4.43"W x 3.94"H
UPC	192790621159
Unit Count	1.0 Count
Warranty Description	2 Year Manufacturer

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$78.59

Duties & taxes included

In stock

Sold byAmazon USADelivered byDesertcartCustomer service byDesertcartReturns14 days · 30 with PRO

Buyer Protection · Full refund if your order doesn't arrive as described.

Desertcart purchases this item on your behalf and handles shipping, customs, and support to USA.

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TrustScore 4.5 | 7,300+ reviews

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