The eight stages

Stages 3 to 10. There are easier problems in the collection, but the list starts at AMC 10 level; below that you don't need an ordering, you need a textbook.

Stage 3

AMC 10/12, early questions 260 problems 9% proof-based

Start stage 3 →

Stage 4

AMC 12 late, AIME early 340 problems 12% proof-based

Start stage 4 →

Stage 5

AIME late 400 problems 34% proof-based

Start stage 5 →

Stage 6

National olympiad, first round 400 problems 68% proof-based

Start stage 6 →

Stage 7

National olympiad second round; IMO P1/P4 300 problems 80% proof-based

Start stage 7 →

Stage 8

IMO Shortlist mid-range; USAMO P2/P5 180 problems 86% proof-based

Start stage 8 →

Stage 9

IMO P2/P5; hard shortlist 80 problems 99% proof-based

Start stage 9 →

Stage 10

Hardest shortlist tier 40 problems 100% proof-based

Start stage 10 →

A note on stage 10

Stages 3 to 9 are placed by measured difficulty. Stage 10 isn't. Nothing in the source data records which shortlist problems were the hardest ones, so these forty are simply the top of the hardest group rather than problems held against a fixed standard. Worth knowing before you read too much into the number.