ByteDance Seed Finds Periodic Weak Spots in Chunked KV-Cache Compression

ByteDance Seed researchers found that language models compressing their KV cache in fixed-size chunks retrieve the same information unevenly depending on token position.

In a 128K-token needle-in-a-haystack test, base DeepSeek-V4 checkpoints differed by up to 40.2 percentage points by phase, and post-training narrowed but did not eliminate the gaps.

The authors urge evaluating such models across positional phases, since high average accuracy can hide systematic failures.