At a predetermined block height, miners begin creating blocks with different rules, and this will cause a bifurcation of the Bitcoin blockchain. The original Bitcoin blockchain will continue on unaltered, but a new branch of the blockchain will split off. The new branch is a distinct blockchain with the same transaction history as Bitcoin up until the fork, but then diverges from it. As a result of this process, a new cryptocurrency is born.

If you had BTC in Coinomi at exactly the time of the fork, it's super easy to access and claim the forked coins: Collecting your forked coins from Coinomi

If you had BTC in a different wallet at the time of the fork, you can still get them using Coinomi, as long as you fully control the address where the coins were: How to get BTC forked coins from many wallet/software/services

If you had a BTC balance in an exchange at the time of the fork, you were not in control of the coins, and cannot claim them using Coinomi. You will only be able to claim them if the exchange decides to start supporting the fork.

The dates and block heights when the supported forks were born are:

  • Clams (CLAM): May 12th 2014 (BTC block 300,377, LTC block 565,693, DOGE block 218,556)
  • Bitcoin Cash (BCH): August 1st 2017 (BTC block 478,558)
  • Bitcoin Gold (BTG): October 23rd 2017 (BTC block 491,407)
  • Bitcore (BTX): November 2nd 2017 (BTC block 492,820)
  • Bitcoin Atom (BCA): January 24th 2018 (BTC block 505,888)
  • Litecoin Cash (LCC): February 18th 2018 (LTC block 1,371,111)
  • Bitcoin Private (BTCP): February 28th 2018 (BTC block ?, ZCL block ?)
  • Callisto (CLO): March 5th 2018 (ETC block 5,500,000)

Bonus questions:

Q: When can I move my BTC?

A: As soon as the BTC block is past the number scheduled for the fork, you are free to transfer your BTC without altering your balance of the forked coin.

Q: What if the transaction sending coins to Coinomi was still unconfirmed when the fork happened?

A: That transaction was not yet included in a block. So as far as the fork is concerned, it never happened.

Q: Can I get forked coins from a paper wallet?

A: Yes, as long as the paper wallet had BTC at the time of the fork.

Q: Can I sweep the forked coin from a paper wallet without sweeping the BTC?

A: Yes, you can sweep each coin separately. Simply go to "... / Sweep wallet" and choose which one you want to sweep. If there are any other coins in the wallet, they will remain untouched until you decide to sweep them. It is recommended to sweep the most valuable coin first.