pre- vs post-LLM paradigms for four classic tasks. (1) Text classification — before: TF-IDF/BOW + LR/GBDT feature engineering, or BERT's [CLS] into
softmax(W⊤h[CLS]); after: zero/few-shot prompts assign labels, or distill into a small model for cost. (2) NER — before: sequence labeling BiLSTM-CRF over BIO tags; after: LLMs emit JSON entity lists, unconstrained label sets, new entity types with zero training. (3) MT — before: SMT (phrase statistics) to NMT (Seq2Seq + Attention, BLEU); after: one multilingual model plus glossary constraints in-context. (4) Summarization — before: extractive (TextRank) and abstractive (BART/Pegasus, ROUGE); after: Map-Reduce chunked summarization for very long documents.