You are building a structured data extraction system using Claude.

Option A is the most sustainable open-world design. The property-type domain is demonstrably not closed: uncommon values already occur, and new labels continue to appear. An enum is appropriate only when the valid vocabulary is stable and exhaustive. If the source contains a legitimate value outside that vocabulary, the schema either rejects it or pressures the model to map it inaccurately. A free-form string preserves the source meaning, while deterministic post-processing can normalize “studio,” “loft,” “duplex,” and future terms into an evolving canonical taxonomy. Anthropic’s Structured Outputs documentation distinguishes structural schema conformance from the semantic decisions made within that schema; it also documents that JSON Schema constraints such as enums govern allowable output shapes and values. Few-shot mapping to the nearest existing enum, option B, discards real distinctions. Continually expanding the enum, option C, creates recurring schema changes and still lags newly observed values. An “other” bucket with detail, option D, is workable but collapses all emerging categories at the primary field and complicates analytics until downstream interpretation occurs. Capturing the raw type first and normalizing it in code provides lossless extraction, testable mappings, and forward compatibility.

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