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Amazon S3 Express One Zone

S3 Express One Zone (launched 2023) is S3's first SSD-backed, single-AZ storage class, designed specifically to minimise object-access latency for workloads where hot data lives next to compute within a single Availability Zone.

(Source: sources/2025-03-14-allthingsdistributed-s3-simplicity-is-table-stakes)

Design choices

  • SSD media — first non-HDD-anchored storage class in S3.
  • Single-AZ by design — Warfield: "we designed as a single-AZ offering to minimize latency." Accepts loss of cross-AZ resilience in exchange for tail-latency reduction.
  • Positioned for workloads where the client already localises compute to one AZ (e.g. ML training jobs, latency-sensitive analytics, hot cache tiers in front of S3 Standard).

Role in S3's performance story

S3's throughput story was already solved for most use cases via the systems/aws-crt parallelization model (GPU instances pushing "hundreds of gigabits per second in and out of S3"). Express One Zone closes the latency gap that the standard class leaves open when workloads move from "batch throughput" to "interactive". Anthropic is cited as a TB/s-class customer pulling in this direction; media- streaming directly from S3 is another.

Caveats

  • No published median/p99 latency numbers in the 2025 post.
  • Single-AZ durability model makes it unsuitable for data of record; customers typically pair it with S3 Standard for durability.

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