Comment by Inufu

> You don’t have to randomize the first part of your object keys to ensure they get spread around and avoid hotspots.

Sorry, this is absolutely still the case if you want to scale throughput beyond the few thousand IOPS a single shard can serve. S3 will automatically reshard your key space, but if your keys are sequential (eg leading timestamp) all your writes will still hit the same shard.

Source: direct conversations with AWS teams.