I am starting playing with DT4 and it look really nice!
Hovewer I by mistake checking in the option to speak chat response, and unfortunately it was a long summary of pdf. Could the option to stop generating the response might be added? it would be also useful in case of text response
If I am too fast and this is planned, I apologise; might my comment help to prioritize features 
Thanks for the nice comments!
Did you try pressing the Clear button?
Clearing the output works, but it seems that it doesn’t stop a query that has already been sent from continuing to process.
My comment was meant more generally.
As a user familiar with various chat clients, I was expecting the interface to have both a button to send a query to the chat and a button to interrupt or cancel a running query. In DEVONthink, I haven’t seen such a button yet. I know that this is still in beta, but I think adding such a button/function in future would be helpful. Alternatively, the “Send” button could change to a “Stop” button while a query is being processed—similar to how it currently shows a spinning icon to indicate it’s working.
The suggestions are noted.
Disabling the option again should stop speaking immediately.