11. The system of claim 10 , the operations further comprising determining, by the completion engine of the query processing system, that the intermediate transcription of the utterance is of a threshold size, wherein the intermediate transcription of the utterance is determined to be associated with the previously received search query only after determining that the intermediate transcription is of the threshold size.
10. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: receiving, from a digital assistant device or mobile device and by a front end-server of a query processing system that includes (i) the front-end server, (ii) a continuous speech recognizer, (iii) a completion engine, and (iv) a search engine, audio data encoding an utterance received at the digital assistant device or the mobile device; obtaining, by the continuous speech recognizer of the query processing system, an intermediate transcription of an initial portion of the utterance; before the continuous speech recognizer generates a final transcription of the entire utterance: i) determining, by the completion engine of the query processing system, that the intermediate transcription of the initial portion of the utterance is associated with a previously received search query, ii) obtaining, by the search engine of the query processing system, one or more results that are identified as responsive to the previously received search query, and iii) storing, by the front-end server of the query processing system, one or more of the results; obtaining, by the continuous speech recognizer of the query processing system, the final transcription of the entire utterance; determining, by the completion engine of the query processing system, that the final transcription of the entire utterance is also associated with the previously received search query; and in response to determining that the final transcription of the entire utterance is also associated with the previously received search query, providing, by the front-end server of the query processing system, the stored one or more results for output without submitting the final transcription of the entire utterance to the search engine.