Lesson 2: Subwords, how models read words they never saw
55 min read·14 Oct 2026
Module 2 · Lesson 2 · About 40 minutes · Needs: basic Python, and what a word token is (Lesson 1 of this module)
The situation
Monday 14 September 2026, project week 2. Dev forwards a test-split message from 25 August: "I got your email about battery batch VB-0426. My pack has that code and the battery runs flat very quiickly. What happens now?" A battery-batch fault: the kind he needs first.
A word list built from the training messages holds every word here except the typo "quiickly", so a word-level model sees an unknown. This lesson replaces words with subwords, pieces smaller than a word, so nothing is ever unknown. This message runs through every section.