Which year / model introduced eco mode?

I'm wanting to buy a subaru legacy wagon (currently living in New Zealand) and was wanting to know what year model introduced economy mode. I have looked online but can't find an answer to which is the earliest model legacy to come with the feature.

Also, does it make much of an impact in fuel consumption? any help with this would be greatly appreciated!!!

I have a 91 Liberty/Legacy GX AWD Auto 1st gen wagon, running on original ej22 boxer flat 4, currently on 187xxx kms. Mostly stock, well maintained, and rare to find in its condition. I live in Australia.

Also unsure of when eco-mode was introduced (Legacy introduced in 1989, and going by my 1991 which has eco-mode, narrows it down), though I can tell you you're looking at a reduction of 0.1L-0.3L fuel use over 100kms, which is definitely noticeable. If you're not going to be smashing the accelerator and braking hard.. this is awesome to have. Most of the time I drive in eco-mode, though sometimes I enjoy making use of the punchy lower-end torque for fun. Also keep in mind your air-con will suck back the fuel the higher it is set too.

Just keep doing your homework, and talk to enthusiasts/mechanics where possible. Hope you can lay your hands on something decent mate