IPSW Portal

Choose aProduct→Choose aPlatform→Choose aVersion→ClickDownload

Download 4.3.1 (15T5545b) for Apple Watch Series 3 (42mm, LTE)

Version:	4.3.1
Build:	15T5545b
Signed:	No
Size:	0.1 GB
Release Date:	2018-04-16 17:04:41
Upload Date:	2018-04-12 16:53:16

Secure download directly from Apple's servers