Backwards Compatibility Guide

Ensuring that you can upgrade your applications easily and smoothly is important to us. That’s why we only break compatibility at major release milestones. You might be familiar with semantic versioning, which is the general guideline we use on all CakePHP projects. In short, semantic versioning means that only major releases (such as 2.0, 3.0, 4.0) can break backwards compatibility. Minor releases (such as 2.1, 3.1, 3.2) may introduce new features, but are not allowed to break compatibility. Bug fix releases (such as 2.1.2, 3.0.1) do not add new features, but fix bugs or enhance performance only.


Deprecations are removed with the next major version of the framework. It is advised to early on adapt your code already each minor as outlined in the deprecation comments and the migration guides.

To clarify what changes you can expect in each release tier we have more detailed information for developers using CakePHP, and for developers working on CakePHP that helps set expectations of what can be done in minor releases. Major releases can have as many breaking changes as required.

Migration Guides

For each major and minor release, the CakePHP team will provide a migration guide. These guides explain the new features and any breaking changes that are in each release. They can be found in the Appendices section of the cookbook.

Using CakePHP

If you are building your application with CakePHP, the following guidelines explain the stability you can expect.


Outside of major releases, interfaces provided by CakePHP will not have any existing methods changed. New methods may be added, but no existing methods will be changed.


Classes provided by CakePHP can be constructed and have their public methods and properties used by application code and outside of major releases backwards compatibility is ensured.


Some classes in CakePHP are marked with the @internal API doc tag. These classes are not stable and do not have any backwards compatibility promises.

In minor releases, new methods may be added to classes, and existing methods may have new arguments added. Any new arguments will have default values, but if you’ve overridden methods with a differing signature you may see fatal errors. Methods that have new arguments added will be documented in the migration guide for that release.

The following table outlines several use cases and what compatibility you can expect from CakePHP:

If you… Backwards compatibility?
Typehint against the class Yes
Create a new instance Yes
Extend the class Yes
Access a public property Yes
Call a public method Yes
Extend a class and…
Override a public property Yes
Access a protected property No [1]
Override a protected property No [1]
Override a protected method No [1]
Call a protected method No [1]
Add a public property No
Add a public method No
Add an argument to an overridden method No [1]
Add a default argument value to an existing method argument Yes

Working on CakePHP

If you are helping make CakePHP even better please keep the following guidelines in mind when adding/changing functionality:

In a minor release you can:

In a minor release can you…
Remove a class No
Remove an interface No
Remove a trait No
Make final No
Make abstract No
Change name Yes [2]
Add a public property Yes
Remove a public property No
Add a protected property Yes
Remove a protected property Yes [3]
Add a public method Yes
Remove a public method No
Add a protected method Yes
Move to parent class Yes
Remove a protected method Yes [3]
Reduce visibility No
Change method name Yes [2]
Add a new argument with default value Yes
Add a new required argument to an existing method. No
Remove a default value from an existing argument No
Change method type void Yes
[1](1, 2, 3, 4, 5) Your code may be broken by minor releases. Check the migration guide for details.
[2](1, 2) You can change a class/method name as long as the old name remains available. This is generally avoided unless renaming has significant benefit.
[3](1, 2) Avoid whenever possible. Any removals need to be documented in the migration guide.


In each minor release, features may be deprecated. If features are deprecated, API documentation and runtime warnings will be added. Runtime errors help you locate code that needs to be updated before it breaks. If you wish to disable runtime warnings you can do so using the Error.errorLevel configuration value:

// in config/app.php
// ...
'Error' => [
    'errorLevel' => E_ALL ^ E_USER_DEPRECATED,
// ...

Will disable runtime deprecation warnings.