End-of-Sequence Token

End-of-sequence token is the special vocabulary token that marks logical completion of a sequence during training and inference - it is the canonical boundary signal in autoregressive language modeling.

What Is End-of-sequence token?

• Definition: Dedicated tokenizer symbol indicating sequence termination.
• Training Role: Teaches model when output should end in supervised objectives.
• Inference Role: Decoder typically stops when EOS token is generated.
• Notation: Often referenced as EOS in model and tokenizer configuration.

Why End-of-sequence token Matters

• Completion Accuracy: Reliable EOS behavior prevents needless continuation text.
• Cost Efficiency: Early natural stopping lowers token usage.
• Format Correctness: Supports clean boundaries in multi-turn and structured interactions.
• Model Interoperability: Consistent EOS handling is required across runtimes and checkpoints.
• Safety: Acts as one layer of bounded-generation control.

How It Is Used in Practice

• Config Verification: Ensure EOS IDs match tokenizer files and serving runtime settings.
• Prompt Design: Avoid accidental EOS-like patterns in special-control token spaces.
• Behavior Monitoring: Track EOS stop rates and long-tail generation anomalies.

End-of-sequence token is a core termination token in all sequence-generation systems - stable EOS handling is essential for predictable and efficient inference.