Block unveils Dessa, an AI voice model trained only on human conversation

Jack Dorsey’s Block has introduced Dessa, an AI model it describes as trained “from scratch on nothing but human conversation.” No books, no web pages, no text of any kind. Just people talking. The pitch is realism. The demos show a model that handles timing, interruptions, laughter and pauses with surprising ease. They also show it calling a user “Ronaldo” for no clear reason, which is a very human mistake in its own way. What Block actually built Dessa launched on October 23, 2026, through a page at block.xyz/dessa and a round of posts on X. Block’s internal AI research lab is behind it, led by Ragavan Thurairatnam. The name has history. Thurairatnam co-founded the original Dessa, an AI startup that Block acquired in 2020. Several members of that team now staff the lab, so the brand has come full circle as a product name. The model is speech-to-speech. Audio goes in and audio comes out, with no detour through written words along the way. Its defining trick is that it runs in full-duplex mode. Picture the gap between a walkie-talkie and a phone call. With a walkie-talkie, one person talks while the other waits for “over.” On a phone call, both sides can speak and listen at once, w...