---
type: Glossary Term
title: val_bpb (Validation Bits Per Byte)
description: "A performance metric for language models measuring how efficiently a model compresses validation data. Calculated as bits per byte of text, lower values indicat"
resource: "https://www.contextstudios.ai/glossary/val-bpb"
category: tech
language: en
timestamp: "2026-03-08T05:32:13.590Z"
---

# val_bpb (Validation Bits Per Byte)

A performance metric for language models measuring how efficiently a model compresses validation data. Calculated as bits per byte of text, lower values indicate better compression and thus better model performance. Used as the optimization target in Karpathy autoresearch because it is automatically computable, requiring no human judgment between iterations.