That’s incorrect. Only refs+dosync use stm. https://clojure.org/reference/refs

Not atoms.

From Hickey’s History of Clojure paper:

“ Taking on the design and implementation of an STM was a lot to add atop designing a programming language. In practice, the STM is rarely needed or used. It is quite common for Clojure programs to use only atoms for state, and even then only one or a handful of atoms in an entire program. But when a program needs coordinated state it really needs it, and without the STM I did not think Clojure would be fully practical.”

https://dl.acm.org/doi/pdf/10.1145/3386321

Atoms do an atomic compare and swap. It’s not the same thing.