[brandonpelfrey]

I'm fairly certain the entire game can be encoded in 16 bits. Thinking through this now. There are much less than 9! Games if you only include valid moves and actually end games that have three in a row. This is also before any symmetries are used.

[zokier]

https://news.ycombinator.com/item?id=39462056 claims that pruning saves only one bit which is not great. I don't know can you squeeze two bits from symmetries somehow?