On the other hand, throwing an additional language model like GPT and BERT into the mix can help if you don't have a ton of voice data. In my attempt to do this, a large portion of the improvement came from letting the language model read the previous sentences in the conversation[2]. AFAIK most commercial systems are blissfully unaware of your previous sentences, leading to conversations like "set an alarm"/"sure when?"/"eightam"/"your nearest ATM is...".
A word of caution though: letting BERT/GPT edit the outputs also gives a (potentially) much more dangerous failure mode: if the speech signal is difficult to understand, the resulting transcript will be difficult for humans to identify as transcription failures.
For example, "yeah, I dunno I haven't..." (read on a noisy phone line in an obscure dialect) was transcribed as "yeah yeah not that is I I am then" by the baseline speech system. After we let BERT edit the outputs, the transcript became "yeah that's not what I was saying...". Which, ironically, was definitely not what the person was saying.
[1] https://arxiv.org/abs/1911.08460, page 9
[2] https://arxiv.org/abs/2110.02267
edit: clarify why previous sentences matter
Obviously it wouldn't be as good as a real person, but it'd be a nice leap to the 95%+ level of accuracy over the 80%ish on high performing commercial STT systems.
The number of homonyms (and near-homonyms) in English in huge
It's been a major issue for some users of W3W (eg https://cybergibbons.com/security-2/why-what3words-is-not-su...)