Tsinghua Reveals 'Referential Dangling' Flaw in Hard Prompt Compression

Tsinghua · hf · 2026-08-10

Research from Tsinghua University identifies a structural failure in hard prompt compression called 'referential dangling.' When algorithms independently score and retain high-relevance text chunks, they often split dependent evidence pairs. This leaves answers without the necessary entity definitions, making them uninterpretable.

Experiments show that at a 0.30 compression ratio, all tested mainstream compressors exhibit dangling rates up to 60% on multi-hop QA datasets. Even advanced models like GPT-5.5 cannot absorb this loss, showing an 8.8 percentage point accuracy drop compared to full contexts.

To fix this, the researchers trained a compact classifier to rank omitted sentences and automatically reinsert missing referential backgrounds during inference. This restoration improves accuracy by 4.7 points on HotpotQA while barely changing the compression ratio (from 0.30 to 0.31).

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