1. A method comprising: performing, by a user device, automatic speech recognition (ASR) on received utterances, wherein performing the ASR includes: generating feature vectors based on the utterances, updating the feature vectors based on feature-space speaker adaptation parameters, transcribing the utterances to text strings, wherein the transcriptions are based at least in part on an acoustic model and the updated feature vectors, and updating the feature-space speaker adaptation parameters based on the feature vectors; transmitting, by the user device, a representation of at least some of the utterances to a computing device for development of an updated acoustic model; after transmitting the representation, receiving, by the user device, the updated acoustic model from the computing device, wherein the updated acoustic model is based on the representation; and replacing, by the user device, the acoustic model with the updated acoustic model, wherein the feature-space speaker adaptation parameters are updated more frequently than the acoustic model is updated, and wherein the acoustic model is updated when the computing device has received a threshold extent of the representations from the user device.