I tried out the preview of UE4.5 to make sure the animation bug that affected 4.4 in Yosemite has been resolved in 4.5. However, UE4.5 does not appear to start on Yosemite GM candidate and just crashes. I compiled using Xcode 6.0.1.
Log as below:
[2014.10.05-01.02.54:528][ 0]LogAIModule: Creating AISystem for world NewWorld
[2014.10.05-01.02.54:591][ 0]LogDerivedDataCache: Saved boot cache 0.06s 47MB ../../../Engine/DerivedDataCache/Boot.ddc.
[2014.10.05-01.02.54:606][ 0]LogInit: Texture streaming: Enabled
[2014.10.05-01.02.54:679][ 0]LogMac: === Critical error: ===
SIGABRT: abort() called
[2014.10.05-01.02.54:680][ 0]LogMac: abort Address = 0x8e9e1b73 (filename not found) [in libsystem_c.dylib]
__cxa_bad_cast Address = 0x8b578a21 (filename not found) [in libc++abi.dylib]
_ZL26default_unexpected_handlerv Address = 0x8b5a09d1 (filename not found) [in libc++abi.dylib]
_ZL15_objc_terminatev Address = 0x898bd6c6 (filename not found) [in libobjc.A.dylib]
_ZSt11__terminatePFvvE Address = 0x8b59e0a1 (filename not found) [in libc++abi.dylib]
__cxa_rethrow Address = 0x8b59dd48 (filename not found) [in libc++abi.dylib]
objc_exception_rethrow Address = 0x898bd4e4 (filename not found) [in libobjc.A.dylib]
-[NSConcreteTask launchWithDictionary:] Address = 0x970286a4 (filename not found) [in Foundation]
_ZN19FMacPlatformProcess10CreateProcEPKwS1_bbbPjiS1_Pv Address = 0xaee5351 (filename not found) [in UE4Editor-Core.dylib]
_ZN19FDesktopPlatformMac12OpenLauncherEb7FString Address = 0x11fc80c4 (filename not found) [in UE4Editor-DesktopPlatform.dylib]
_ZN13UEditorEngine10InitEditorEP11IEngineLoop Address = 0x1058615e (filename not found) [in UE4Editor-UnrealEd.dylib]
_ZN13UEditorEngine4InitEP11IEngineLoop Address = 0x10589ffc (filename not found) [in UE4Editor-UnrealEd.dylib]
_ZN15UUnrealEdEngine4InitEP11IEngineLoop Address = 0x10a80a5c (filename not found) [in UE4Editor-UnrealEd.dylib]
_ZN11FEngineLoop4InitEv Address = 0xad66d76 (filename not found) [in UE4Editor]
_Z10EditorInitR11IEngineLoop Address = 0x10a7f739 (filename not found) [in UE4Editor-UnrealEd.dylib]
_Z11GuardedMainPKw Address = 0xad6b355 (filename not found) [in UE4Editor]
-[UE4AppDelegate runGameThread:] Address = 0xad735e5 (filename not found) [in UE4Editor]
-[FCocoaGameThread main] Address = 0xae8abf4 (filename not found) [in UE4Editor-Core.dylib]
__NSThread__main__ Address = 0x96eeab7a (filename not found) [in Foundation]
_pthread_body Address = 0x97c192fc (filename not found) [in libsystem_pthread.dylib]
_pthread_body Address = 0x97c19279 (filename not found) [in libsystem_pthread.dylib]
thread_start Address = 0x97c174b1 (filename not found) [in libsystem_pthread.dylib]