I’m sorry if this has been discussed, I can’t seem to find any concrete discussion about this, but is there any difference between A4 and the A4 Keys other than the keyboard/controller?
Is the synth engine identical?
Just out of curiosity.
The synth engines are the same, although there is some internal differences in the AK that I believe they refer to as “finely tuned”.
That said, if I dial up the same patch on both it usually sounds exactly the same. The AK seems more FULL at times but it’s not hugely noticeable.
The other differences are keys, joystick, and button placement.
And individual track outs.
I had an Analog Four for one year. Then recently sold it to buy an AK.
Got the Ak on yesterday. And… that’s a perfect piece of gear, really.
With the same projects, same kits, to my ears (but maybe I’m wrong or maybe I’m high), the bass presets sounds better. It’s like bass sounds are more “round”, they are a bit warmer.
The AK is really - as described by Elektron - a keyboard/synth for live Performances.
The Joystick is amazing and reveals to me a new face of the A4. Sounds are alive. And I’m sure that joystick movements will be recordable in the sequencer in a next update.
You have a direct access to the MidiMap: 
You have a HOLD button: hold a 3 fingers chords and play a 1 finger melody 
You have a BIG knob to browse sounds anytime you want 
Separate outputs 
Lights that indicates the notes that are played and have been recorded
I’m completely done! No regrets at all to have sold the A4!