What is the difference between BERT and GPT?

BERT and GPT are both transformer-based models designed for natural language processing, but they differ fundamentally in architecture, training objectives, and use cases. BERT (Bidirectional Encoder Representations from Transformers) is optimized for understanding language context in both directions (left-to-right and right-to-left) using an encoder-only architecture. GPT (Generative Pre-trained Transformer), in contrast, is a decoder-only model designed for autoregressive text generation, predicting the next word in a sequence using only left-to-right context. These structural differences lead to distinct strengths and applications.

Architecturally, BERT processes entire input sequences at once, allowing it to capture bidirectional context. For example, in the sentence “The bank account was near the river,” BERT can disambiguate “bank” (financial institution vs. riverbank) by analyzing surrounding words in both directions. GPT, however, generates text sequentially, making it inherently unidirectional. This makes GPT better suited for tasks like writing coherent paragraphs or code, where the model predicts each subsequent token based on prior words. Training objectives also differ: BERT uses masked language modeling (hiding random words to predict them) and next-sentence prediction, while GPT uses causal language modeling (predicting the next word in a sequence). These methods shape how each model handles context—BERT excels at deep text understanding, while GPT prioritizes fluent generation.

Practically, developers choose BERT for tasks requiring semantic analysis, such as question answering, sentiment classification, or named entity recognition. For instance, BERT can determine if “Apple” in a sentence refers to the company or the fruit by evaluating bidirectional context. GPT is preferred for generative tasks like chatbots, text completion, or code synthesis, where output coherence matters. A developer might use GPT-3 to draft an email or generate Python code based on a prompt. Additionally, BERT is typically fine-tuned on labeled datasets for specific tasks, while GPT often leverages few-shot or zero-shot learning via prompts. When deciding between them, consider whether the task requires deep bidirectional understanding (BERT) or sequential generation (GPT), and the availability of training data for fine-tuning.