Localising Context Length Degradation in a Mixture of Experts Language Model: Retrieval Head Collapse, Not Router Failure
Long-context "context rot" (accuracy degradation as input length grows, even when task difficulty is held fixed) is localized here to a specific, causal mechanism inside a small Mixture-of-Experts language model (OLMoE-1B-7B-0924), then tested for generality across two further architectures. Forced-choice retrieval acc...