Is this 64 or 32 bit PowerShell today?

On PowerShell version 4.0 and up:

[Environment]::Is64BitProcess

More thorough again...

# Is this a Wow64 powershell host
function Test-Wow64() {
	return (Test-Win32) -and (test-path env:\PROCESSOR_ARCHITEW6432)
}

# Is this a 64 bit process
function Test-Win64() {
	return [IntPtr]::size -eq 8
}

# Is this a 32 bit process
function Test-Win32() {
	return [IntPtr]::size -eq 4
}

Source

See also