Caching
The caching system has been rewritten.
Documentation
Files Affected
Entity API
entity_load() has been removed.
Documentation
Files Affected
Info File
Module info files' core key must have a value of 8.x.
Documentation
Files Affected
Info files must contain a type key.
Documentation
Files Affected
Many common dependencies have moved into core.
Documentation
Files Affected
Module info files' configure key must be a route name, not a path.
Documentation
Files Affected
Miscellaneous
Many common functions, shared variables, and constants have been renamed.
Documentation
Classes must be PSR-4 compliant.
Documentation
Automated web tests must be in a PSR-4 namespace, and unit tests must be converted to PHPUnit.
Documentation
System
l() has been removed.
Documentation
Files Affected
Utilities
drupal_strtolower() has been moved into the Unicode utility class.
Documentation
Files Affected