How do I use OpenAI for text classification?

To use OpenAI for text classification, you can leverage either the completions API for direct classification or generate text embeddings to train a custom classifier. Both approaches rely on OpenAI’s language models, such as GPT-3.5 or GPT-4, but differ in implementation and use cases. The choice depends on factors like dataset size, required accuracy, and whether you need real-time predictions or offline batch processing.

For direct classification using the completions API, structure your prompt to include examples of text and their corresponding labels. For instance, to classify sentiment, you might provide a prompt like: "Classify the sentiment of these tweets as Positive, Neutral, or Negative. Example: ‘I love this product!’ → Positive. Text: ‘The service was slow.’ →". The model will infer the pattern and return the label for the new text. You can adjust parameters like temperature (lower for deterministic outputs) and max_tokens to limit responses. This method works well for small-scale tasks or prototyping, but it can become costly for large datasets due to per-API-call pricing. Additionally, you’ll need to handle output parsing to extract labels consistently.

A more scalable approach involves using OpenAI’s embeddings API. Generate embeddings (dense vector representations) for your text data, then train a lightweight classifier like a logistic regression or SVM on top of these embeddings. For example, if classifying support tickets into categories like “Billing” or “Technical,” first convert each ticket into an embedding using text-embedding-3-small. Store these embeddings, then use them as input features for a classifier. This separates the heavy lifting of text understanding (handled by OpenAI) from the classification logic (handled locally), reducing API costs and enabling bulk processing. Tools like scikit-learn or PyTorch can train the classifier, and you can fine-tune it as needed without further API calls. This method is ideal for large datasets or when labels require domain-specific adjustments.

Consider trade-offs between the two methods. The completions API is simpler to implement but less cost-effective for high volumes. Embeddings require more setup but offer better long-term scalability. For highly specialized tasks, you could fine-tune a base OpenAI model using your labeled data, though this demands significant compute resources and technical expertise. Always validate performance with a test set and monitor API usage to avoid unexpected costs. Tools like the OpenAI Cookbook on GitHub provide code examples for both approaches, making it easier to adapt these strategies to your specific use case.