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FeatureArc measured coding agents on features they extend themselves, and pooled success fell from 62.7 percent at stage one to 28.5 percent overall

AspireAI community · arXiv (Hunyuan Team, Tencent)
*Most feature benchmarks evaluate a single request on a fixed codebase, but real features evolve: each extension builds on code written earlier, so a coding agent has to keep the feature correct on its own earlier code.* FeatureArc evaluates coding agents on evolving features, with a pipeline that constructs tasks from repository histories, combining dependencies between successive stages of the same feature, explicit requirements and interface contracts, and executable checks across four programming languages. Ten coding agents were evaluated on 73 manually reviewed tasks of 2 to 10 stages, each agent working in one persistent session without external test feedback or rollback. Pooled success fell from 62.7 percent at the first stage to 28.5 percent when the whole feature is tested on the final code. Inherited defects were present in 72.9 percent of failed later stages, and in stages following a failure agents left the earlier error unnoticed about 95 percent of the time. At Tencent the pipeline extends internal evaluations to this setting and guides development of the Hunyuan model family.
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One distance function matched sparse-autoencoder features across layers and compressed feature circuits into supernodes
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.
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