As often with Teac, available in quite a few versions : from the 1966 A-4000 and A-4000S, the A-4010, the A-4010S (1967) and the ultimate A-4010GSL in 1973.
I believe the A-4010SL to have been export-only (but I could be wrong.)
Compared to the 1960s versions, the A-4010SL brought SLH tape compatibility, separate bias & eq selectors, slightly different cosmetics and switchable meters (tape or source display) and meters' scale (+3dB) to allow better monitoring when using SLH tapes.
SLH, or Low-Noise / High-Ouptut tape, have a higher saturation point and lower inherent noise so recording levels can go further in the red :) By 3dB.
The automatic reverse mode was retained from the earlier models : automatic being if one has previously glued a piece of conductive foil at one end (or both) of the reel tape - a very manual automation in the end. Also necessary for this planned-in-advance automation : a second play head !
Soon to vanish, the center button (between the reels) sets tape tension for 1mil or 1/2 mil tapes.
The rest is early 1970s mid-end Teac : two eddy current outer-rotor motors, one hysteresis synchronous for capstan, wide-dynamic rec/play amplifiers with mic/line mixing etc.
Replaced by the A-4010GSL in 1973 with a swap of the Permalloy heads for entirely new HD Ferrite heads (but a permalloy core) and the replacement of the 1/2mil button by a "rec pause" function.