No-Repeat N-Gram

No-repeat n-gram is the hard decoding constraint that blocks generation of any n-gram already produced earlier in the output - it is a strict safeguard against repeated phrase loops.

What Is No-repeat n-gram?

• Definition: Constraint rule that forbids duplicate n-token sequences during generation.
• Mechanism: At each step, candidate tokens that would recreate an existing n-gram are masked out.
• Parameter: The n value controls strictness, with larger n allowing more flexibility.
• Applicability: Works with beam search and sampling-based decoding flows.

Why No-repeat n-gram Matters

• Degeneration Control: Prevents common repetitive loops in long-form generation.
• Readability: Reduces duplicated clauses and improves narrative flow.
• Deterministic Safety: Provides hard guarantees where soft penalties are insufficient.
• Production Reliability: Useful for public-facing assistants where repetition is highly visible.
• Quality Consistency: Stabilizes output under high-entropy sampling settings.

How It Is Used in Practice

• Choose N Carefully: Start with moderate n values and validate against fluency regression.
• Domain Testing: Check technical tasks where exact phrase reuse may be necessary.
• Combined Policies: Use with light penalties instead of excessive hard blocking where possible.

No-repeat n-gram is a strong structural guardrail for repetitive generation failures - it is highly effective but must be tuned to avoid over-constraining valid output.