Context Window

Every six months, someone declares RAG dead. The argument is always the same: “Now that GPT-4.1 has 1M tokens and Gemini 2.5 Pro handles 2M, why bother with retrieval? Just dump everything into context.” I’ve been building production RAG systems since the LlamaIndex 0.5 days, and I can tell you: bigger context windows didn’t make RAG obsolete. They made the problem more interesting — and harder to get wrong. Here’s what the 2026 data actually shows, and what techniques deliver real results when you’re building a retrieval system that needs to work in production. ...

Llama 4 Scout is Meta’s open-weight model with a 10 million token context window — the largest of any open-weight model released in 2026. At roughly 4 tokens per line of code, that covers approximately 2.5 million lines of code in a single prompt. In practice this means you can load an entire mid-size production repository — including tests, docs, and config — without chunking, vector databases, or retrieval pipelines. ...

Context windows have grown 2,500x in three years — from GPT-3’s 4K tokens in 2023 to Qwen Long’s 10M tokens in 2026. That growth is real, but advertised token counts and actual usable context are very different things. If you’re choosing a model for long-document analysis, agentic workflows, or codebase Q&A, the headline number will mislead you. This guide cuts through the marketing to compare GPT-4.1, Claude Opus 4.6, and Gemini 2.5 Pro on what actually matters: real retrieval performance across context lengths, cost at scale, and hidden pricing traps you’ll only discover on your first big invoice. ...