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What is a context window? Definition and business implications
The context window is the maximum amount of text an AI model can process in a single query, measured in tokens. It includes the prompt sent and the response to produce. Beyond this limit, the model loses access to the oldest information of the exchange.
The context window is a technical characteristic of the model, fixed at construction. For GPT-3 in 2020, it was 4,096 tokens, that is, about 3,000 words or 6 pages. In 2026, frontier models exceed one million tokens: Claude Opus 4.6, Claude Sonnet 4.6, GPT-5.4, and Gemini 3.1 Pro all have one million tokens (about 750,000 words, or 1,500 pages), with Llama 4 Scout announcing ten million. This expansion radically changes the possible use cases. You can inject a complete dossier, an entire knowledge base, a conversation history of several months. But beware: declared size and effective quality diverge. Context decay research (notably at Chroma and Anthropic) shows that model precision drops on information placed in the middle of very long contexts. For critical cases, a tight, well-structured context is preferable to an 800,000-token dossier dumped in bulk.
Concrete example
In December 2022, GPT-3.5 accepted 4,096 tokens as input, that is, about 3,000 words. In March 2026, Anthropic released Claude Sonnet 4.6 in general availability with a one-million-token window, at standard pricing (3 dollars per million input tokens, 15 per million output). In three years, single-call ingestion capacity has been multiplied by 244. Concretely, a law firm can submit the entirety of a client file (contracts, exchanges, case law) in a single prompt, where it would have previously needed to orchestrate a RAG with vector database. The architectural simplification is radical, the cost also kept in check.
See also
Sources
- Claude's 1M context window now generally available, Anthropic, March 2026. https://www.anthropic.com/news
- What is a context window?, IBM Think 2026. https://www.ibm.com/think/topics/context-window