T5

T5 is a Google encoder-decoder transformer that reformulates all NLP tasks as text-to-text problems — both input and output are text strings regardless of task type. Pre-trained on the C4 corpus with a masked span denoising objective, T5 and its variants (T5-XXL, Flan-T5) are widely used for summarization, translation, and question answering.

Flan-T5 adds instruction tuning across 1,800 tasks.