What is the slowest delivery guarantee level in Kafka?

The slowest delivery guarantee level in Kafka is "at most once" (no more than once).

At this level, messages may be lost, but they will never be delivered more than once. This minimizes delays and overhead but reduces delivery reliability.

For comparison:

• At least once — guarantees delivery at least once, duplicates may occur.
• Exactly once — guarantees delivery exactly once, the most reliable but requires additional resources and configurations.

"At most once" is suitable for scenarios where losing some messages is acceptable, but speed and minimal delay are important.