Google has been testing undo and redo buttons in beta versions of Gboard for a while now, and it's finally ready for stable ...

Undo can reverse per-letter deletion. Redo is great for undoing accidental Undo.

Gboard for Android is getting undo and redo options. You can put them in your suggestions bar now, if you want.

The redo button appears in the suggestions row, once you try to undo something using Gboard. Once you type something using Gboard, you can easily use undo and redo to, well, undo or redo things!