11-9
May 18. The question is just 11-9. Format [solution] TOMI [TOMI], prefixes 923, 0 and 6. The author expected it to be "solved at sight".
It wasn't. Players tried subtraction, Roman numerals, Atbash, block 2's key. One player announced "Solved!" with 119 TOMI november top posted. The prize didn't move. Hint 1 a day later: the idea came from a Wikipedia article. Hint 2 the day after: the article is about the number 9.
K is the 11th letter. 11-9 is K-9, said like "canine". So the answer is K-9 and the TOMI field is police dog. Good boy.
Funded twice
There's a twist in the post itself. The author funded the block while writing it, then forgot and funded it again on the day of the post. Two outputs of 7 mBTC on one address. "Whoever solves this block walks away with 14 mbtc instead of 7." No taking it back, the author says.
So after hint 2, a race. Several players solved it within minutes. The first claim confirmed at 14:01:29 UTC, splitting one output into two 2.5 mBTC halves with a 2 mBTC fee. The second, at 14:14:29, took the other output. u/silver_anth wrote they "got double spent and lost the prize". u/Quantris posted KyVcQKeGXy, the start of the key, as proof they had it too.
A lottery, as the author put it. So who got which output? The chain doesn't say. The record keeps both claims and names nobody. Nobody printed the whole key, so the record derives it.