To address the high failure costs caused by blind actions of LLM agents in software engineering, researchers proposed the Speculative Uncertainty (SU) method. This method utilizes a lightweight open-source draft model that only outputs tokens to perform a single forward scoring on the trajectories generated by the agent, without needing to access logits, weights, or repeated sampling. By separating the inference and action phase features and calibrating them to verifiable targets, SU generates failure probability scores for direct use by downstream strategies. Experiments with Qwen3-Coder-480B and Claude 3.5 Sonnet showed that this method reduced the execution error rate during deployment by 6-8 percentage points and decreased Token costs by 14-19%. Additionally, SU can be migrated to out-of-distribution benchmarks without re-training and achieves cross-model generalization.