How Go Maps Work: From Buckets to Swiss Tables

Hey Mates!

“How does a map work in Go?” is one of my favorite interview questions. It sounds simple, but it opens up a conversation about hashing, collisions, memory layout, and why two implementations with the same average O(1) lookup complexity can behave quite differently. With Go 1.24, that conversation got more interesting: the map implementation switched to Swiss Tables. Let’s walk through how the old implementation worked, what changed, and how the new design finds your keys.

TL;DR

Go 1.24, released in February 2025, completely replaced the internal implementation of the built-in `map` with a design based on Google's Swiss Tables. The syntax and the behavior guaranteed by the Go specification did not change, so existing programs required no migration. In microbenchmarks, some map operations became up to 60% faster. Across the Go team's full-application benchmark suite, geometric mean CPU time improved by about 1.5%. Datadog reported roughly 70% less memory for one exceptionally large map—an impressive case study, not a universal promise.