Checklist IOAI 2026 Individual Contest · Task 5
Ghost of the Machine
Find the character position at which each English passage switches from human-written text to a language-model continuation.
The task
The story is that books in a national archive have been quietly altered. Each sample is one English passage that begins as human writing and, at a hidden point, carries on with text a language model generated from the human part. Read as a whole, it seems like one coherent piece.
Every passage has exactly one switch. Each side has at least 180 words, and passages total about 500 to 800 words. You predict the character offset where the human part ends: everything before it is human, and everything from it onward is machine-written.
Scoring rewards getting close, not only being exact, since each sample's score decays exponentially with the distance in characters. The only pretrained weights allowed are those of the bge-base-en-v1.5 text encoder, which may be used frozen or fine-tuned. Classical feature-based models are unrestricted.
Abridged by SOTA from the official materials. The official statement has the exact rules, and it wins wherever this summary differs.
At a glance
- You get
- JSONL passages ({"id", "text"}):
dataset/trainhas 1,221 samples withanswers.jsonl, anddataset/test_publichas 380 samples with a development copy of answers. At grading timetest_publicis replaced by hidden sets of 380 samples without answers:test_leaderboard_afor the public leaderboard andtest_leaderboard_bfor the final ranking. - You submit
answers.jsonlat the repository root, with one {"id", "boundary_char_index"} object per sample; the index must be an integer in [0, len(text)], and a missing, non-integer or out-of-range entry scores 0 for that sample. Submit a single notebook named exactlysolution.ipynb.- Scoring
- Per sample exp(−|p − t| / τ) with τ = 100, where p is the predicted and t the true boundary character index; the final score is the mean over the split on a 0–100 scale.
- Rules
- Time limit 10 minutes wall-clock, covering any grade-time training or fine-tuning plus inference
- One GPU (≈16 GB VRAM), no internet, 5 GB storage
solution.ipynb≤ 20 MB- Only pretrained model: bge-base-en-v1.5 (110M-parameter text encoder), frozen or fine-tuned on train; classical and statistical tools are unrestricted
- Format
- Individual Contest, Day 2 (the 2026 Contest Rules give six hours for the day's three tasks); the same task was set in the GAITE Contest with a hint