You should augment your knowledge about what you know - it all changed Monday.
https://platform.openai.com/docs/assistants/tools/knowledge-retrieval
Knowledge Retrieval
Retrieval augments the Assistant with knowledge from outside its model, such as proprietary product information or documents provided by your users. Once a file is uploaded and passed to the Assistant, OpenAI will automatically chunk your documents, index and store the embeddings, and implement vector search to retrieve relevant content to answer user queries.
The embedding engine is likely the same text-embedding-ada-002 we know. It does semantic similarity search, and can match topics across languages. Its fluency is based on training similar to ChatGPT, but it is a smaller model.
When using the model directly instead of through the new assistant feature, it doesn’t have its own document system. You have to add knowledge to the API call yourself.