Duolingo DE from AR versions:

Trees:
2016-01-10, ? skills Beta
2016-05-27, ? skills 
2021-10-16, 120 skills (= 120 different lessons)
Paths:
2022-09-10, 120 skills (= 120 different lessons), 78 units
2023-09-11, 118 skills (= 118 different lessons), 78 units
2024-05-01, 118 skills (= 118 different lessons), 137 units (?)
2024-05-10, 120 skills (= 120 different lessons), 120 units
2024-08-18, 120 skills (= 120 different lessons), 120 units, CEFR A1
2025-03-15, 70 skills (= 70 different lessons), 70 units, CEFR A1

Edited by Mat!/Ozone, 2025 03 18.