  We study the zero-shot transfer capabilities of text matching models on a
massive scale, by self-supervised training on 140 source domains from community
question answering forums in English. We investigate the model performances on
nine benchmarks of answer selection and question similarity tasks, and show
that all 140 models transfer surprisingly well, where the large majority of
models substantially outperforms common IR baselines. We also demonstrate that
considering a broad selection of source domains is crucial for obtaining the
best zero-shot transfer performances, which contrasts the standard procedure
that merely relies on the largest and most similar domains. In addition, we
extensively study how to best combine multiple source domains. We propose to
incorporate self-supervised with supervised multi-task learning on all
available source domains. Our best zero-shot transfer model considerably
outperforms in-domain BERT and the previous state of the art on six benchmarks.
Fine-tuning of our model with in-domain data results in additional large gains
and achieves the new state of the art on all nine benchmarks.
