I tried to find an answer to understand what does it mean and how painful it is for me when a Bitcoin Gold (BTG) hard fork happens. So, I found an answer in this document that is not available at the time of my post and I used the cached version of it.
Step 1: The hard fork occurs: a ‘snapshot’ of the blockchain is taken
Usually a hard fork will happen at the same time when Bitcoin reaches the fork block. However, Bitcoin Gold uses a different way to launch the hard fork: by “taking a snapshot” of the Bitcoin blockchain before the fork block height 491407. Instead of forking immediately, the Bitcoin Gold p2p network will launch a few days later from that snapshot.
When Bitcoin reaches the block 491407, nothing special will happen. Bitcoin block 491407 will be mined with SHA256 as normal. No block will be mined in the Bitcoin Gold p2p network because it is not launched yet.
However, when the full node client of Bitcoin Gold is ready a few days later, instead of mining from the latest Bitcoin block, Bitcoin Gold will start to mine its own 491407th block on top of block 491406. Bitcoin Gold full nodes will only accept a block 491407 that is mined with Equihash, so they will not recognize BTC block 491407 as a valid BTG block.
At the same time, Bitcoin already have a longer blockchain. That’s why it’s called a “snapshot hard fork”. We didn’t follow the common realtime hard fork pattern because a PoW change means there will always be a gap between the fork block.
The first Equihash block will be block 491407 of the Bitcoin Gold blockchain, and from that point on GPU miners participating in the Bitcoin Gold network will begin mining more Equihash blocks on top of it. In this way, the Bitcoin blockchain will bifurcate and a new coin - Bitcoin Gold (BTG) - will be created. Everyone who holds BTC at block 491406 will then control an equal amount of coins on the BTG blockchain branch, which can be spent at any time in the future with the corresponding private keys.
And what about next step.
Step 2: The BTG blockchain is activated
If you have BTC in a paper wallet, hardware wallet, multi-signature address, or any other form of secure private key storage, you will be able to spend your corresponding BTG at any time in the future. There is no expiration date for your BTG. If you have BTC in cold storage that you did not plan to touch for many years, do not change your plans because of this fork. Your BTG will still be there decades from now.
In 491407 hard fork is the one and only opportunity to get initial BTG. After that time, your options to acquire it will be to buy it on an exchange like any other cryptocurrency, to mine it with your own computer hardware (GPUs), or to earn it by trading your goods and services for it.
Cryptocurrency exchanges are custodial businesses, which means they control your private keys, not you. When the Bitcoin Gold fork occurs on block height 491407, any exchange that is holding BTC on your behalf will also receive the corresponding BTG. While they should credit your account with the equal amount of BTG, there is no legal authority that can force them to do so. The Bitcoin Gold home page will display the names and logos of exchanges that have promised to credit their users with BTG at the 1:1 ratio. If your exchange is not shown, please consider transferring your BTC to a supporting exchange or withdraw to a personal wallet where you control the private keys.
If you have your funds in an exchange then go to it and find out what it says about your Bitcoin Gold tokens.
Bitfinex published news about Bitcoin Gold Chain Split Tokens and Bitcoin Gold Hard fork rules.
“Snapshot Event” means a snapshot of the Incumbent Bitcoin Blockchain that will used as an initial UTXO set for alternative mainnet blockchain based on—and that may only be used exclusively based on—the consensus protocol of Bitcoin Gold. A Bitcoin Gold snapshot is scheduled to occur at Block Height 491406;
Here is the Block Height 491406 that happened 8 hours ago:
Height 491406
Block Time Tuesday, October 24th 2017, 4:17:35 +03:00
Arrival Time Tuesday, October 24th 2017, 4:17:53 +03:00
Size 985.3 kB
Difficulty 999999999999.99999999
Version v20000000
So, what happens with our bitcoins?
With respect to the Bitcoin Gold CSTs, we will be following the general methodology outlined in our recent Statement Regarding Upcoming Segwit2x Hard Fork. Specifically, and subject to our terms and conditions, when the designated block is mined (491406), we will take a snapshot of all relevant balances and positions. Lenders will receive both BTC and BTG. Any user that is short BTC/USD or long any BTC trading pair (ETH/BTC, LTC/BTC, etc.) will owe BTG to the financing counterparty, effectively making the user short BTG. An exception is being made where BTC is borrowed but is not in use as financing collateral. In that case, BTG will accrue to the lender. Users that are financed long BTC/USD or short any BTC trading pair will receive BTG. We will only be assigning BTG to balances greater than or equal to 0.01 BTC.
New token names on Bitfinex:
1.1“BG1” means a CST representing the Incumbent Bitcoin Blockchain;
1.1“BG2” means a CST representing Bitcoin Gold consensus protocol;
1.1“BTG” means a Digital Token converted from BG2s at or after Contract Settlement, as set out in these T+Cs;