10. The system of claim 8 , the operations further comprising: in response to classifying the utterance, based at least on a portion of the aligned transcription, as the voice command: generating the voice command using at least a portion of the first transcription and at least part of the second transcription; and initiating the voice command; and in response to classifying the utterance as the voice query: generating the voice query using at least a portion of the first transcription and at least part of the second transcription; and initiating the voice query.
8. A system comprising: a data processing apparatus; and a non-transitory memory storage storing instructions executable by the data processing apparatus and that upon such execution cause the data processing apparatus to perform operations comprising: receiving audio data that corresponds to an utterance; obtaining a first transcription of the utterance that was generated using a limited speech recognizer, wherein the limited speech recognizer comprises a speech recognizer that includes a language model that is trained over a limited speech recognition vocabulary that includes one or more terms from a voice command grammar, but that includes fewer than all terms of an expanded grammar; obtaining a second transcription of the utterance that was generated using an expanded speech recognizer, wherein the expanded speech recognizer comprises a speech recognizer that includes a language model that is trained over an expanded speech recognition vocabulary that includes all of the terms of the expanded grammar; aligning the first and second transcriptions of the utterance to generate an aligned transcription; and classifying the utterance based at least on a portion of the aligned transcription, as a voice command or a voice query.