It's really 8 models that are 220B, which is not the same as one model that is 1.7T params. There have been 1T+ models via mixtures of experts for a while now.
Note also the follow up tweet: "since MoE is So Hot Right Now, GLaM might be the paper to pay attention to. Google already has a 1.2T model with 64 experts, while Microsoft Bing’s modes are different mixes accordingly"
There is also this linked tweet https://twitter.com/LiamFedus/status/1536791574612303872 - "They are all related to Switch-Transformers and MoE. Of the 3 people on Twitter, 2 joined OpenAI. Could be related, could be unrelated"
Which links to this tweet: "Today we're releasing all Switch Transformer models in T5X/JAX, including the 1.6T param Switch-C and the 395B param Switch-XXL models. Pleased to have these open-sourced!"
Anyway... remember not to just read the headlines, they can be misleading.