Option D identifies the dominant capacity problem. Anthropic states that everything sent in a request counts toward the context window : the system prompt, messages, documents, tool results, tool definitions, and the output Claude generates. A 175,000–190,000-token document is therefore not the complete input. Adding a 2,500-token tool schema, system instructions, wrappers, and the reserved output budget can push a nominally sub-200,000-token document close to or beyond the effective limit. Anthropic also warns that more context is not automatically better and that accuracy and recall can degrade as token count grows, a behavior described as context rot. That combination explains why short documents remain accurate while long documents lose information. Option A predicts a problem independent of document length, contradicting the measurements. Option B is an unsupported generalization and does not account for tool-definition overhead. Option C recognizes long-context degradation but ignores the concrete evidence that hidden prompt components consume the same window. The correct response is to count tokens for the complete request before submission, reserve output capacity, and chunk or retrieve relevant sections when the total approaches the model’s supported window.

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