---
title: Breaking changes in CMS 10
slug: cms-12/docs/breaking-changes-in-cms-10
docTags: 
createdAt: 2026-08-10T15:55:57.000Z
---

To view the complete list of changes, see the [release notes feed](/epiui/CMS/Content/documentation/Release-Notes,,82523/?epieditmode=False).

Some changes are binary breaking but do not necessarily require code changes but rather a project recompilation. Breaking changes are changes in method signatures or behavior of methods compared to the documented API in the previous version, which is described in this document.

## The new ".Internal" namespaces

One of the bigger changes is that all APIs were reviewed to find internal implementation classes and that those were moved to internal namespaces. You can see exactly which APIs are affected in these stories: [CMS-3762](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3762) (Episerver CMS Core) and [CMS-3755](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3755) (Episerver CMS UI). Read more about these changes in [Henrik Nyström's blog post](/epiui/CMS/Content/blogs/Henrik-Nystrom/Dates/2016/10/introducing-changes-to-reduce-our-public-api,,163468/?epieditmode=False).

## Event system

The event system (used primarily for communication between instances in a load-balanced environment) will no longer guarantee that events are processed sequentially, one at a time. Code that uses the event system should be reviewed for thread safety and cannot rely on the order in which events arrive to the event listener.
Implementors of custom event providers should also be aware that SendMessage calls are no longer guaranteed to run in a separate thread and should, therefore, take precautions to ensure optimal performance.

## Remove support for legacy dot notation for dojo modules

Optimizely is removing the support for the legacy dot notation for dojo modules, for example, `epi-cms.editing.ContentPicker`. This means that you need to change all `EditorDescriptors`, `Components` and so on where you have defined your Dojo modules using the `.` to `/`. Read more [CMS-2295](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-2295) and in [Ben McKernan's blog post](/epiui/CMS/Content/blogs/Ben-McKernan/Dates/2016/9/the-dot-notation-breaking-change,,155420/?epieditmode=False).

## EPiServer.Shell moved to EPiServer.CMS.UI.Core

`EPiServer.Shell.dll` was moved from NuGet package `EPiServer.Framework` to `EPiServer.CMS.UI.Core`. If you have both packages installed, no change is required. Read more in [CMS-1380](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-1380).

:::hint{type="info"}
**Note**
If you get an error message saying *Value cannot be null.Parameter name: virtualPath]in EPiServer.Shell.ShellInitialization.WaitForInitializeModules()...*, remove the `EPiServer.Shell.dll` from the site bin folder. This may happen for sites that do not have the `EPiServer.CMS.UI.Core` installed, for example Commerce Manager.
:::

## Converting the database to UTC is a required step

Running the database with local date and time will no longer be supported ([CMS-1449](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-1449)). A database not converted to UTC will throw an exception to avoid data loss caused by mixing local and UTC date and time. Conversion can be done before upgrading for versions 9.1 or later, for example, using the provided PowerShell scripts, see [Storing UTC date and time in the database](/epiui/CMS/Content/documentation/Items/Developers-Guide/Episerver-CMS/9/Deployment/storing-utc-date-and-time-in-the-database,,139840/?epieditmode=False) for more details. A setting can be added to the `appSettings` section of `web.config` to disable the exception if the site temporarily have to be started without doing the conversion, add `episerver:DisableDateTimeKindValidation` with value `true`.

### More breaking changes in UI:

- [CMS-4925](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-4925) Objects of type `epi._Dependency` can no longer be created
- [CMS-1202](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-1202) `GetContentByPermanentLinkQuery` will always return the content without work id
- [CMS-2710](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-2710) Dialog now has `destroyOnHide:true` by default
- [CMS-4319](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-4319) The value of `enum ExtendedVersionStatus.Expired` have changed
- [CMS-1150](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-1150) Calling `watchModelChange` and u`nwatchModelChange` on `_Command.js` has been deprecated

### More breaking changes in Core:

- [CMS-4110](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-4110) The event args in the post event `MovedContent` will now contain the content loaded after the move
- [CMS-3852](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3852) `ContentStore` methods for saving data has been removed
- [CMS-3756](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3756) `IAvailableModelSettingsRepository` method signature changes
- [CMS-3763](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3763) `ContentScannerExtension` method signature changes
- [CMS-3166](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3166) `ContentSearchHandler` changed to an abstract class
- [CMS-3131](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3131) `LocalizationService` now returns fallback language before fallback defined in code
- [CMS-1197](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-1197) `LanguageBranch` now implements `IReadOnly` and `LanguageBranch.URLSegment` will now return the `LanguageID` if not set to a custom value
- [CMS-1320](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-1320) Browsing to expired page will now return a 404
- [CMS-1266](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-1266) No longer allowed to have the wildcard host as the only host for any given language
- [CMS-2078](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-2078) Align status transitions, events and required access rights when saving
- [CMS-3824](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3824) `UrlSegment` have been replaced with `IUrlSegmentCreator`/`IUrlSegmentLocator`/`IUrlSegmentGenerator`
- [CMS-3823](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3823) `SiteDefinitionRepository` and `SiteDefinitionResolver` have been replaced with `ISiteDefinitionRepository` and `ISiteDefinitionResolver`
- [CMS-3090](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3090) Added validation of virtual content type properties defined on interfaces
- [CMS-3153](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3153) `IContentVersionRepository` list methods have been consolidated into one. `PageVersion` is obsoleted.
- [CMS-3449](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3449) `PropertyResolver` changed to an abstract class
- [CMS-3530](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3530) New method `ImportProperties` introduced on `IContentTransfer`
- [CMS-3591](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3591) `HostDefinitionExtensions.FirstOfType` return wildcard host last
- [CMS-3764](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3764) `AdministrationSettingsService` is replaced with `IAdministrationSettingsService`
- [CMS-3854](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3854) Extended `IContentEvents` with events `RequestingApproval` and `RequestedApproval`
- [CMS-3859](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3859) Create a language branch of a non-localized content should not be possible
- [CMS-3860](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3860) `GetDefault` when content implements `ILocale` but now `ILocalizable` will not set language
- [CMS-1206](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-1206) `IContentVersionRepository.Delete` method will now throw an exception when a version cannot be deleted
- [CMS-3982](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3982) New event `ContentSecuritySaving` added to `IContentSecurityRepository`
- [CMS-3983](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3983) Event args type changed on `ContentLanguageSettingRepository`
- [CMS-3987](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3987) `PropertyDate.Date`/`PageData.StartPublish`/`PageData.StopPublish` are now nullable
- [CMS-4167](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-4167) `ContentCoreData.StartPublish`/`StopPublish` properties are now nullable
- [CMS-3812](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3812) Empty properties were changed to work more like standard .NET properties
- [CMS-3991](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-3991) Methods removed from `IPermanentLinkMapper`
- [CMS-4149](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-4149) Experimental setting `UseLegacyValueType` from EPiServer 7 to return legacy value types has been removed
- [CMS-2807](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-2807) `ContentLanguageSettings` were replaced with `IContentLanguageSettings` and `ContentLanguageSettingsResolver`
- [CMS-4445](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-4445) Delay publish job is now impersonating the user that scheduled the publish
- [CMS-4537](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-4537) `IScheduledJobStatusService.ReportExecutedJob` method signature changed
- [CMS-4219](https://world.optimizely.com/documentation/Release-Notes/ReleaseNote/?releaseNoteId=CMS-4219) `PropertyLinkCollection` no longer inherits `PropertyXhtmlString`. It is now a direct base class to `PropertyLongString`.