Wow, what a secret! It's not like Google has been consistently writing papers about this the whole time or anything. Oh wait:

2022 LaMDA: https://arxiv.org/abs/2201.08239

2020 chat bot: https://arxiv.org/abs/2001.09977

2018 bert: https://arxiv.org/abs/1810.04805

2017 LLM: https://arxiv.org/abs/1706.03762