Duolingo EN from UK, versions:

Trees:
v0: 2014-05-01  ? (Beta)
v0: 2014-08-12  ? (Beta)
v1: 2015-09-01, 55 skills (55 different lessons)
v2: 2022-01-10, 83 skills (83 different lessons)

Paths:
1.0: 2022-09-01, 55 skills and 40 stories (95 different lessons) (42 units) 
2.0: 2023-07-12, 83 skills and 40 stories (123 different lessons) (60 units)
3.0: 2023-08-08, 91 skills and 66 stories (157 different lessons) (68 units) CEFR A1
4.0: 2023-08-20, 190 skills and 203 stories (393 different lessons) (128 units) CEFR B1
2.1: 2023-09-01, 83 skills and 66 stories (149 different lessons) (55 units) CEFR A2
5.0: 2023-11-05, 252 skills and 323 stories (575 different lessons) (179 units) CEFR B2
6.0: 2024-03-05, 277 skills and 323 stories (600 different lessons) (295 units) CEFR B2
2.2: 2024-05-01, 83 skills and 83 stories (166 different lessons) (95 units) [Schools]
2.3: 2024-05-10, 83 skills and 83 stories (166 different lessons) (83 units) [Schools]
6.1: 2024-05-10, 277 skills and 323 stories (600 different lessons) (258 units) CEFR B2
7.0: 2024-12-20, 305 skills and 320 stories (625 different lessons) (305 units) CEFR B2
7.4: 2025-06-01, 305 skills + 343 stories + 743 radios = 1391 different lessons (305 units) CEFR B2
7.4: 2025-06-30, 305 skills + 665 stories + 1257 radios = 2227 different lessons (305 units) CEFR B2
8.0: 2025-09-10, 313 skills + 800 stories + 1257 radios = 2370 different lessons (1005 units) CEFR B2
8.1: 2025-12-01, 1019 skills + 966 stories + 1257 radios = 3242 different lessons (1005 units) CEFR B2

JSON References and links:
tree_en_uk_b1_ch3_AMEE
tree_en_uk_b2_ch5_AMEE
tree_en_uk_v1_new
tree_en_uk_v2_existing
tree_en_uk_v3_new
tree_en_uk_v4_existing

https://liuch.github.io/duolingo_courses_overview/
https://duolingo.fandom.com/wiki/Course_list
https://duolingodata.com/
https://duolingodata.com/oldtable.html
https://ardslot.com/duolingocrowns.html

Edited by Mat!/Ozone, 2025/12/05.