Fun fact: The consensus between professional go and chess players is that all new AI systems (alphago, etc) have really revitalised the game and introduced incredible amount of new strategies and depth.
I wish alphago was more "democratized" -- that is to say, I have many questions and experiments I'd love to run on it (a friend of mine and I have frequently pondered Go played in various different topological spaces, and I'd love to see an AI's result, for example).
Look into Katago. It's an open source AI in the same general style as AlphaGo, with an empasis on training speed. On 9x9 you can get up to superhuman really quickly on just a decent home machine (I think hours/days, can't remember exactly and it's probably improved since I looked).
You can also just download pre-trained models. Get those set up and then install Sabaki (https://sabaki.yichuanshen.de/) and connect it to your KataGo... instant (ok, a few hours probably if it's your first time setting it up) superhuman Go AI. There's even an npm package you can use to process SGF files and automatically score moves as good/questionable/bad + generate variations that were better choices: https://github.com/9beach/analyze-sgf/blob/master/README.en-...
(Edit: Misread what the other poster was trying to do, but I'm leaving this here as a reference for anyone else who just wants to use KataGo on their own machine on their own Go games.)
He'd been playing Go professionally for 24 years. I never said he ragequit. He's too great a man to do something like that. Lee instead apologized for his losses, stating "I misjudged the capabilities of AlphaGo and felt powerless" while emphasizing that the defeat was his own and "not a defeat of mankind". I imagine being the Hector of humanity is quite a burden to bear. His professional ratings then took a dive for a few years https://www.goratings.org/en/history/ before he announced his retirement. To this day he remains the only human being who's ever won a single game against AlphaGo.
He's the last human to ever beat the strongest Go AI. I don't know if he's happy about it, but he'll have a special place in the history books because of that. And like Chess, the game of Go will continue to be played and loved.
I don't want to pull back the curtain too much, but surely DeepMind foresaw the possibility of AlphaGo winning and then Lee Sedol losing confidence or interest in the game, which would generate a load of bad publicity for them.
So it would make sense for DeepMind's contract with him to contain a clause requiring him to continue playing go professionally for a few years (but not necessarily put much effort into it), as well as the standard non-disparagement clauses.
In fact, I wouldn't be surprised if AlphaGo was programmed to throw the forth game after securing the win with the first three of the five games. That gives Lee some bragging rights, and makes for a more hopeful story than "Computer stomps likeable human".