Pre-generation success probes estimate response correctness from a language model's hidden activations before decoding, enabling cost-aware routing.
While prior work has demonstrated their utility primarily on English inputs, we study their reliability across languages along three dimensions:
- (1) whether they preserve the ranking of likely successes and failures (DISCRIMINATION)
- (2) whether they retain probabilities that match observed success frequencies (CALIBRATION)
- (3) whether they produce scores comparable enough across candidate models for cost-aware multilingual routing (UTILITY)
Using 3,000 MATH problems in 10 languages and 8 open-weight model configurations, we compare cross-lingual transfer from English-trained probes and equal-budget pooled multilingual probes.
English-trained probes retain useful cross-lingual discrimination but become less well calibrated after transfer.
Pooled multilingual supervision improves both properties and yields more reliable estimates of success.
In routing experiments, the pooled router achieves a 0.7% higher test success rate while reducing modeled cost by 13.0% relative to always selecting the model with the highest average success.
These results show that multilingual routing requires success estimates that remain well calibrated and comparable across languages and models.