In short, everything that is not namespace/module compatible will be deprecated/changed/removed in the future, so it is not recommended to use it.
a.2) #Array asClassInEnvironment: Smalltalk globalsb.1) Smalltalk globals at: #Array
=> Ok-ish, note that you may need to change 'Smalltalk globals'��the namespace/module when support for those will be added since Array will be in a module.
Maybe you want instead to use instead:
c) self class environment at: #Array
=> this will work in the future if your code is a class which environment/namespace/module includes the Array class you would expect
a.1) #Array asClass
b.2) Smalltalk at: #Array
b.3) Smalltalk classNamed: #Array
=> In which namespace/module are you looking for #Array ? In the future this may be removed, alternatively it will work only for globals but not globals inside namespace/module which won't work since Array will be in a module.