This morning I got a 5mm chunk of glass in my tire which produced a flat. The gash in the tire was 5mm long and I had to dig residual glass out of it. While doing this I pulled the gash open and it looked like the tire was cut enough to expose the strands present in the next layer. I was able to replace the tube and ride home (I was just about 1km away). With the tire inflated you can still see a slit where the glass went through but there is no bulging and the tube does not appear to be pushing through the slit. Is this tire a good candidate for repair or must it be replaced?

I'd replace it. That's a lot of the cords being cut and chances are the extra load that is now being put onto the cords on each side means that they will fail sooner or later.

Besides, a tire boot is intended as a temporary fix to get you home so you can do a proper tire replacement.

The old rule of thumb is that if the belting threads are cut, the tire is shot.

I know that it is possible to repair automotive tires with punctures, but I am not sure how effective this is with bicycle tires with higher psi.

If the bike is an around-town machine, use the damaged tire on the rear and ride her until she fails. Otherwise, if you go on distance rides where an unfixable flat would be very inconvenient, then change the tire.

Sadly, most tires retire because of damage rather than because they are ridden thin.

I replaced the tire. The new one comes on and off a LOT easier so should be easier to fix in a roadside situation.