My thoughts are that the instructions for these things SUCK.
They'll say 240V and then throw at you "3-wire", which could mean 120/240v, or 240V including the ground.

I'd wait until you get it, unless you can confirm for certain the requirements.

Does the manual show a wiring diagram. How about calling the manufacturer?

If it says it can live with 240/208, I doubt highly it gives a hoot about the grounded conductor (i.e. neutral). Does it show the connections. Unless it has a specific place to land a grounded conductor, I don't think it cares. Never seen an induction cooktop that did. You have a manu/model number, we can look at it for you.

I cannot find any wiring diagram. The model is CI 491 it is a Gaggenau induction cooktop. I have about 300 feet of 6-2 Teck Cable so I was hoping I could use it and save $$$. I was hoping to avoid buying 6-3 if it isn't needed.

The installation instructions are on the Gaggenau web site. there are three wires: black (L1), red (L2), and green (ground).

You only need 6-2.

The above being said, I might be inclined to run 6-3 anyhow just in case some day someone wants to put a different cooktop there that does require the grounded conductor.

"They'll say 240V and then throw at you "3-wire", which could mean 120/240v, or 240V including the ground. "

If they need a neutral they should be labeled as 120/240 V, NOT just 240 V (or 240/208 V).

Look on the nameplate.
It is more likely to be correct since it is used by the agencies that 'list' equipment (like UL).

You could ask for a copy of the listing from the manufacturer.

Its probably a German cooktop where everything runs on 220-40
The green wire is a giveaway. US appliances sometime need 120 for motors and such, and 240 for the heating element (In the case of an electric dryer.)

Its probably a European manufactured cooktop in a country where everything runs on 220-40 (German?)
The green wire is a giveaway. US appliances sometime need 120 for motors and such, and 240 for the heating element (In the case of an electric dryer.)

You can sit there and guess what all you want, but I already pointed out that I had downloaded the installation manual for the thing after he provided the model # AND THERE ARE ONLY L1/L2 (208-240) plus a ground.