FLAN-T5 includes the same improvements as T5 version 1.1 (see here for the full details of the model's improvements.)
Google has released the following variants:

google/flan-t5-small

google/flan-t5-base

google/flan-t5-large

google/flan-t5-xl

google/flan-t5-xxl.

The original checkpoints can be found here.

Refer to T5's documentation page for all API reference, code examples and notebooks. For more details regarding training and evaluation of the FLAN-T5, refer to the model card.