Is there data behind that claim? The Bloomberg Terminal uses up to four and they are not strictly acronyms — sure, WEI is “World Economic Indices”, but TOP is “Top News” and OMON is “Options Monitor”. Four opens up a much wider range of possibilities in English if you don’t strictly use acronyms because there’s a wealth of short words and abbreviations that are super memorable.

a few examples that come to mind: EC2, EMR, ECR, EKS, RDS, EBS, DMS, ECS, VPC, SSS (S3), SNS, SES, IAM,

How does this list show these are easier to remember than ones with four characters?

The claim was that amazon prefers 3 letters, so the list supports that claim.

And of course, AWS.

although in that case agtc is the obvious choice

Amazon Quantum Ledger Database

(QLDB)