Block trained its new speech model on a single Nvidia GB200 NVL72, a liquid-cooled rack that Nvidia says holds 72 Blackwell GPUs and 36 Grace CPUs. The finished model, called Dessa, runs on a MacBook Pro with an M4 Max chip or better, and everything it knows came from human conversation, with no text and no pretrained model underneath.

Block's in-house AI lab put Dessa online Thursday with a demo site full of recorded conversations. Jack Dorsey, Block's co-founder and chairman, promoted it on X that afternoon and added in a reply: "this is big (but also really really small…small enough to run on your macbook)."

Abstract illustration of two overlapping sound waveforms, one coral and one teal, running across a dark plum background, suggesting two voices speaking at the same time.

Why it skips the text step

Most voice assistants work as a relay: one model transcribes the caller, a language model writes the answer and a text-to-speech engine reads it back. Nvidia's open Nemotron Voice Agent blueprint is built that way. Block's lab says that once speech is turned into text, the sarcasm and the frustrated sighs are gone, and it blames that for voice AI that feels "stilted, slow and, worst of all, annoying."

Dessa takes audio in and sends audio out. It is full-duplex, so it keeps listening while it talks, and in one of Block's clips it finishes a movie title the other speaker can't recall. The lab says it learned language from "hundreds of times fewer words" than large language models need.