TraceSpec shows agent speculative-decoding averages hide the failures, and conditions draft training on trajectory state
AspireAI community · arXiv
Agents make many model calls over evolving histories, so the usual aggregate speculative-decoding metrics average away the decisions that matter. TraceSpec combines dynamic execution with fixed-prefix replay and releases TraceSpec-Traj, a corpus of 10,000 training states and 2,500 test states spanning browsing and software engineering. Across five speculative baselines the analysis found aggregate acceptance can rise with context length while declining inside matched late browsing actions, which is what motivates state-conditioned supervision. Training on intermediate assistant turns and allocating a fixed prediction budget using state-conditioned estimates of prefix-aware acceptance gaps improved replay throughput by 12.5% to 22.6% over the DSpark base, and Qwen3-4B ablations showed adaptive allocation raising accepted length by 3.3% to 10.0% over fixed full-turn supervision. The throughput numbers are replay throughput, so the gain on live agent traffic is not something the paper measures directly.
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Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.