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We wanted to write an article related to a very frequent customer question regarding Skype for Business (Skype for Business) Server 2019 to Skype for Business Server Subscription Edition (SE) migration. 

As we mentioned in Skype for Business Server Roadmap Update – there are two ways to migrate to Skype for business server SE: 

1. Traditional (legacy) migration:

The “Add a new Skype for Business Server to your topology and move services/users to it” approach: This is mandatory if you are moving from Skype for Business Server 2015 to Skype for Business Server SE, but is only optional if you are moving from Skype for Business Server 2019 to Skype for Business Server SE. 

2. In-place upgrade:

The “Install Skype for Business Server SE Release to Manufacturing (RTM) build on top of Skype for Business Server 2019 (i.e. simply upgrading your existing 2019 deployment to SE)” approach: This is new, and some customers feel it’s “too good to be true” or possibly risky. 

Let us explain why we view this second approach as “low risk”. 

How RTM of a new Skype for Business Server version used to be created 

In the past, when a new version of Skype for Business Server was released, we would make significant changes to the code base. The following is a simplification, but it gives you a general idea. Usually we would: 

1. About two years before the release of the new version, take a version of the current in-market product as “base code” of the new product 


2. Add and remove a bunch of features 


3. Change installation prerequisites 


4. Set new minimum hardware requirements 


5. Change the major and minor build number in our build system  


6. Close to the release date, port over all features, security and hotfix updates released for the current in-market product since the code paths diverged (because the new version shouldn’t regress in any way) 


7. Change the product name and update the Microsoft Software Licensing Terms 

Because many of those changes were significant, this essentially required customers to do the following: 

• Perform a legacy (side-by-side) migration 

• Do a significant amount of testing in their organizations to ensure that added or removed features do not interfere with their business processes or 3rd party applications 

• Develop training for end users (because of significant product changes) 

• Wait for CU1, because RTM build was seen as “high risk” as many features were added / removed (Note: Waiting was never required/recommended by Microsoft, but we know many customers would wait for at least CU1 before migrating.) 

How we created Skype for Business Server Subscription Edition RTM 

As opposed to the traditional process, Skype for Business Server SE RTM was created as follows: 

1. Started with Skype for Business Server 2019 CU8 as the base code, slightly incrementing the minor build number 


2. Added the recent CU8 Hotfix 1 update from March ‘25 


3. Changed the product name and updated the licensing terms  

Note that the first two items, above, are part of every CU process and we have updated the licensing terms in patch updates in the past, so it is in-scope as a typical kind of change.   

We did not do any of the following in Skype for Business Server SE RTM, compared to Skype for Business 2019 CU8 Hotfix 1 (i.e. March 2025 cumulative update 7.0.2046.548 for Skype for Business Server 2019) 

• Change the major version of code 

• Add / remove any features 

• Fix any bugs that were not already fixed in the March 2025 release 

• Change installation prerequisites or hardware requirements 

Because of all of this, installing Skype for Business Server SE RTM on your Skype for Business Server 2019 deployment is essentially installing Skype for Business Server 2019 “CU9”, with a small payload that could be considered a minor Hotfix. 

Why upgrade then? What’s the point of all this? 

There are several ways in which we believe this approach takes the time pressure off your organizations: 

•  It is a simple “no significant changes since Skype for Business 2019 CU8” installation, so there is no need for extensive testing and validation. 


• By upgrading to this Skype for Business 2019 CU9 SE RTM build, you switch from the Fixed lifecycle policy of Skype for Business 2019 (end of support life on October 14, 2025) to the Skype for Business SE Modern lifecycle policy and your product is supported after October 14, 2025. 


• Even if you want to upgrade your Skype for Business 2019 hardware for Skype for Business SE, you can in-place upgrade to Skype for Business SE first on old hardware and then, once you are on the new support lifecycle path, you have the time to upgrade your server hardware. 

Conclusion 

We realize that with this approach to Skype for Business Server SE RTM, we are doing something different, and we probably did not articulate enough just how different it is. As far as engineering work is concerned, Skype for Business SE RTM is a re-branded “Skype for Business 2019 CU9” with no features, meaning you can upgrade directly from any Skype for Business Server 2019 update, including 2019 RTM, to Skype for Business Server SE. We have released 8 CUs for Skype for Business 2019 already and have a high degree of confidence that this can be a very low risk action for our customers.  

To Recap:  

 The Skype for Business Server Team