I have with Azure. They can be very generous depending on your company state, investment status, current spend, and your ability to switch to a competitor.

Startups are a specific case where you can get access to rather generous credits (note, not the same as an open-ended discount agreement) for a couple of years.

For larger companies operating over the longer term, you would be looking for an EDP agreement, which gives you a discount in exchange for agreeing to a minimum spend threshold over a period of a few years. This would be significantly less than 50%.

The main factor is level of spend. If you can commit to spending $1M over the next 2 years AWS will give you big breaks.