Best API for AI-based long text summary / Q&A?

I want an API that can take long text inputs (e.g. podcast transcripts) , and allow me to summarize and engage with them.

ChatPDF (pic attached) does a great job with this using OpenAI embeddings + Pinecone, but requires me to transform my text files into PDFs.

This feels suboptimal, as I already have underlying text files and want to return answers in text, so I would be converting to pdf just to go back to text.

Does anyone have any recs for good APIs for long text (e.g. 20,000+ words) GPT4+ based summarization and Q&A?