Encodes historical periods, epochs, and broad temporal categories.
What It Does
Time.Era neurons activate on historical periods and broad temporal categories: named historical eras ('the Renaissance', 'the Cold War', 'the Jurassic period'), century-scale references ('the 20th century', 'medieval times', 'antiquity'), technological ages ('the Industrial Revolution', 'the digital age'), and cultural periods ('the Romantic era', 'the Jazz Age'). They encode time as a broad temporal domain rather than a specific point or sequence.
How It Behaves
Era neurons are the single largest element by count in our entire corpus — larger than any other of the 56 elements across all sub-types. This reflects the centrality of historical periodization in language: enormous amounts of human text are organized around historical periods, and models process era references constantly. Era neurons show even distribution across all layers, suggesting they are involved in processing at every stage. They co-activate with Identity neurons (historical figures belong to eras) and Relation neurons (events within eras are related by period).
Research Example
In OLMo 3 7B, Time.Era neurons activate not just on explicitly named periods but on contextual era inference — 'before smartphones existed' triggers Era neuron firing even without naming a specific era, because the model infers the pre-2007 era from the technological reference. This contextual era inference is one mechanism by which models reason about historical context without always naming it explicitly.