SOPO-4B

Official release of the 4B SOPO (Socratic Policy Optimization) model for span-level hallucination detection. See the evaluation instructions for the RAGTruth test set.

RoPE configuration and compatibility

This checkpoint requires a RoPE base (rope_theta) of 5000000, not the default 10000. The original config.json saved with Transformers 5.8.1 contained this value only under rope_parameters.rope_theta. With some older inference stacks, including Transformers 4.57.1 and vLLM 0.14.0, the absent top-level rope_theta can default to 10000 and override the nested value without an error or warning. This can seriously degrade predictions and cause unusually long, token-limited generations.

The updated config.json sets both rope_theta and rope_parameters.rope_theta to 5000000 for compatibility. The model weights are unchanged. If you downloaded the checkpoint before this correction, re-download config.json (or add "rope_theta": 5000000 at the top level of your local copy) before running inference. Check that the effective RoPE base in your serving stack is 5000000, especially when using older Transformers or vLLM versions.

Related resources

• SOPO source code and evaluation script
• RL training dataset
• Reasoning-augmented SFT training dataset