Title: UTC-IE: A Unified Token-pair Classification Architecture for Information Extraction. Abstract: Information Extraction (IE) spans several tasks with different output structures, such as named entity recognition, relation extraction and event extraction. Previously, those tasks were solved with different models because of diverse task output structures. Through re-examining IE tasks, we find that all of them can be interpreted as extracting spans and span relations. We propose using the start and end token of a span to pinpoint the span in texts, and using the start-to-start and end-to-end token pairs of two spans to determine the relation. Hence, we can unify all IE tasks under the same token-pair classification formulation. Based on the reformulation, we propose a \textbf{U}nified \textbf{T}oken-pair \textbf{C}lassification architecture for \textbf{I}nformation \textbf{E}xtraction (\textbf{UTC-IE}), where we introduce Plusformer on top of the token-pair feature matrix. Specifically, it models axis-aware interaction with plus-shaped self-attention and local interaction with Convolutional Neural Network over token pairs. Experiments show that our approach outperforms task-specific and unified models on all tasks in 10 datasets, and achieves better or comparable results on 2 joint IE datasets. Moreover, UTC-IE speeds up over state-of-the-art models on IE tasks significantly in most datasets, which verifies the effectiveness of our architecture.