Anthropic released Claude 2.1, doubling the context window to 200K tokens — about 150,000 words, or 500-plus pages — and reporting a 2x reduction in false statements versus Claude 2.0, a 30% drop in incorrect answers on complex documents, and a three-to-fourfold reduction in misreading a document's claims. It also introduced tool use in beta, letting Claude call external APIs, searches, database queries, and calculators, plus support for system prompts to shape responses. The full 200K context window was reserved for Claude Pro subscribers. The release landed in the middle of OpenAI's board crisis.