Going depth 38 on online Stockfish, lichess analysis says Rxc6+ is +99, while chess.com at depth 40 is convinced that Rxc6+ is a mate in 17.

@TobyBW go deeper, or show the bot by playing the lines. It’s mate in 15 with a4.

@deagol I'm not good enough at chess to know the lines, but I trust you.

@TobyBW play a4, then let it go depth 35+, see what the bot says.

@TobyBW some lines if black doesn’t respond with c5 it’s even shorter mate. for some werid reason the bots refuse to see the b4 pawn sacrifice as worth a faster mate

https://manifold.markets/harfe/manifold-plays-chess-3-if-we-play-3-a16ac846c1bb Rxc6+
https://manifold.markets/harfe/manifold-plays-chess-3-if-we-play-3-33230984dab2 a4

Moves by average probability:

0.461371 Rxc6+

0.334854 a4

--------------------

pick a number between 1 and 999999999 (inclusive)

Outcomes by integer range:

[ 1-999999999] Rxc6+, a4

Hash of the complete table:

edeabdef186b9c5ad8b51d3afa7cfe26050ebbd36ea7818009d4e271bc1f67c2

“There's an old saying about those who forget history. I don't remember it, but it's good.”
― Stephen Colbert

Again engines are weirdly myopic on this perfectly logical a4, b4 idea to get a queen faster for a faster mate. They go depth 40+ without seeing it, but once one shows them by playing both moves, they do get the shorter mating lines at low 30s depth.

Otherwise, the slower but surer pawn gobbling can continue to the predictable end.