Scalable dynamic class language modeling

A system comprising:

• data processing hardware of a user device;
• and
• memory hardware in communication with the data processing hardware and storing instructions, that when executed by the data processing hardware, cause the data processing hardware to perform one or more operations comprising:
• receiving a voice query spoken by a user;
• generating, using a class-based language model, a word lattice representing a candidate transcription sequence for the voice query, the candidate transcription sequence comprising a class-based symbol, the class-based symbol corresponding to a particular class;
• incorporating one or more class-based terms that belong to the class at a location in the word lattice that corresponds to a position of the class-based symbol in the candidate transcription sequence;
• and
• determining a transcription for the voice query that comprises a sequence of terms including one of the one or more class-based terms in place of the class-based symbol in the candidate transcription sequence.