Fields in the BidRequest or BidResponse can occasionally be deprecated.
Deprecated fields eventually sunset, meaning they'll be removed from the
protocol and will no longer work.
The notification period is the amount of time between deprecation and sunset. During the notification period, update your code to remove any dependencies on deprecated fields to ensure uninterrupted service.
Deprecated fields have a [deprecated = true] option, and the following
statement in the first line of their descriptions:
Deprecated. This will be removed in {MONTH} {YEAR}
You might also encounter deprecated field names with a DEPRECATED_ prefix,
which is the legacy way of marking deprecated fields.
Deprecations and sunsets are announced in the release notes and blog.