Best LLM for Long Documents in 2026

Gemini 3 Pro's 1 million token context window is the largest for a fully managed commercial model — roughly 750,000 words. Handles full books, large codebases, and multi-document research sets. AA Intelligence Index 48.44 means it's also more capable than Llama 4 Scout on the actual analysis once it has the document loaded.

Grok 4.1's 2 million token context window is the second-largest among commercial models and covers most enterprise long-document use cases. Strong on reasoning across long contexts. The real-time X data access adds unique capability for research tasks that need current information alongside large documents.

GPT-5.2's 400K context window handles most enterprise document workloads — full contracts, lengthy reports, large codebases. The hallucination rate of 6.2% and strong capability make it the most reliable choice for document tasks where accuracy is critical and your document fits within 400K tokens.

Claude Sonnet's 200K context is smaller than the others here, but its accuracy and coherence across long documents is notably better than GPT-5.2 in head-to-head tests. It maintains detail recall from early in long prompts more reliably — which matters as much as raw context size for many real tasks.