[2602.07672] Debugging code world models

Computer Science > Software Engineering arXiv:2602.07672 (cs) [Submitted on 7 Feb 2026 (v1), last revised 14 Feb 2026 (this version, v2)] Title:Debugging code world models Authors:Babak Rahmani View a PDF of the paper titled Debugging code world models, by Babak Rahmani View PDF HTML (experimental) Abstract:Code World Models (CWMs) are language models trained to simulate program execution by predicting explicit runtime state after every executed command. This execution-based world modeling enables internal verification within the model, offering an alternative to natural language chain-of-thought reasoning. However, the sources of errors and the nature of CWMs' limitations remain poorly understood. We study CWMs from two complementary perspectives: local semantic execution and long-horizon state tracking. On real-code benchmarks, we identify two dominant failure regimes. First, dense runtime state reveals produce token-intensive execution traces, leading to token-budget exhaustion on programs with long execution histories. Second, failures disproportionately concentrate in string-valued state, which we attribute to limitations of subword tokenization rather than program structure. To study long-horizon behavior, we use a controlled permutation-tracking benchmark that isolates state propagation under action execution. We show that long-horizon degradation is driven primarily by incorrect action generation: when actions are replaced with ground-truth commands, a Transformer-...