[slashvar2701]

No, that's the price of typo tolerance and search-as-you-type, until the user validate the query you have no way to distinguish between prefix and full word.

Search-as-you-type is much more a guide during the search, it shows you a preview of possible results from what you've currently typed both as a whole query and as the beginning of a query.

All other variation are worth: no prefix during search as you type means that you'll have an empty result most of the time or things that are completely irrelevant; keeping prefix on the final search means that you'll see a lot of irrelevant results (especially with typo-tolerance).