Translating 300-Page Books with Claude: Taming Token Limits and Chunking Strategies

How we built a reliable pipeline to split long texts for LLM translation without losing context or breaking the bank At LectuLibre, we translate entire books using Claude. The challenge: a 300-page book is roughly 90,000–120,000 words, which translates to 120,000–160,000 tokens. While Claude 3 models have a 200k context window, sending an entire book in one API call is impractical. It's slow, expensive, and often degrades translation quality due to attention dilution. We needed a robust chunking strategy that preserved context and stayed within token limits. The Problem: One Book, Too Many Tokens When we first started building LectuLibre, we naively assumed we could just pass the whole book to Claude and get a translation back. We quickly hit three walls: Rate limits : A single request with 150k tokens triggered API timeouts and 429 errors. Cost : Even if it worked, processing 150k tokens per request with Opus would cost over $13 per book, and most of the input would be wasted on repeated context. Quality : Long contexts tend to make the model "forget" early chapters, leading to inconsistent character names and terminology. Clearly, chunking was necessary. But how do you split a book without losing narrative flow? First Attempt: Naive Splitting by Paragraphs Our initial approach was simple: split the text into chunks of roughly 10,000 tokens by paragraphs. We used a regex to split on double newlines and then concatenated paragraphs until we hit the token limit. import re def split_into_paragraphs ( text : str ) -> list [ str ]: return re . split ( r ' \n\s*\n ' , text ) def chunk_by_paragraphs ( paragraphs : list [ str ], max_tokens : int = 10000 ) -> list [ str ]: chunks = [] current_chunk = [] current_tokens = 0 for para in paragraphs : # Estimate tokens using character count / 4 (quick and dirty) para_tokens = len ( para ) // 4 if current_tokens + para_tokens > max_tokens and current_chunk : chunks . append ( ' \n\n ' . join ( current_chunk )) current_chunk = []