Upgrading from v3.x to v4 is fairly simple. Below are the major changes that are released as a part of CometChat v4: Please follow the Setup instructions to upgrade to the latest V4 version.

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Chat Import Change

Remove all the imports of CometChat Flutter v3 SDK or replace it with single import statement 
import 'package:cometchat_sdk/cometchat_sdk.dart';

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Calling Import Change

Remove all the imports of CometChat Flutter v3 SDK or replace it with single import statement 
import 'package:cometchat_calls_sdk/cometchat_calls_sdk.dart';