How history works
Every read is kept on your Mac, the same passage in the same voice is never spoken twice, and Regenerate says it again when you want it.
Every read Chippy makes is kept. The audio, the text it read and the timing of each word are files in a history folder on your Mac, and they go nowhere else.
Opening history
Press History in the panel's header, or pick History from Chippy's menu in the menu bar. It opens as its own window beside the panel and fills as you read. Each row is the start of the text, how long ago it was read, the voice and the word count. The list shows the fifty most recent reads.
Click a row and that reading opens in the panel, paused at the start. Nothing sounds until you press play. Each row also has Download, which saves the audio to your Downloads folder, and Delete, which asks once in the row and then removes the files.
The same passage is never spoken twice
This is the part worth knowing. Before Chippy sends anything to be spoken, it checks whether it already has a finished recording of the same request: the same text in the same voice. If it does, that recording plays, and nothing is sent and nothing is spent. Read a paragraph again tomorrow and you hear the recording from today.
Pick a different voice for the same text and it is a new read, because the voice is part of what Chippy asks for. The speed slider is not: it changes how fast the recording plays, so a faster listen costs nothing. A read you stopped partway is never reused either: a later read of that passage is spoken in full rather than played back cut short.
When you do want it again
Sometimes the recording is not the one you wanted: you picked the wrong voice, or the reading was cut short, or you simply want to hear it made again. The row under the progress bar has Regenerate. Press it and Chippy speaks the reading the panel is holding again, from scratch, past the check that would otherwise hand you the recording it already has. With nothing loaded the button says there is nothing to regenerate yet.
What you had is kept. Regenerate does not overwrite the old recording or remove it; the new reading arrives in History beside it, the way any new read does, and you can play, download or delete either one.