Sadly no information on how it works, but a generic "multi sig works like this" picture. Does not look like a sidechain.

Looks like people have a bitgo wallet to use this service. This way, bitgo knows the funds are already there. There is no risk for them to do this and the clients get their coins.

It can be instant, because no bitcoins are really moved over the blockchain in the progress.

its a offchain transmission that emulates the onchain transmission..


because they own the keys, they authorized it to go to the destination onchain so they know it will get there, so they are happy to credit the recipient offchain..

because bitgo use multisig, the sender cannot send the funds elsewhere afterwards..
the benefit of it is that people cant try sending the same tx 1000 times in 3 seconds.. as bitgo will only sign the first transaction and only push that first transaction onto the network, allowing bitgo to trust the funds will get to where it suppose to.. and able to credit the recipient before its arrived. because they are the ultimate signer of the tx

imagine it like you already deposited funds into your bitgo account.. which is a multisig authorising bitgo to manage transactions.
and you want to send funds to bitstamp

bitstamp show a deposit address that is also a multisig managed by bitgo

when you send funds from within bitgo 2 things happen

1. bitgo credits bitstamp's bitgo account (sql database) with the funds. and simultaneously
2. send the real transaction via the blockchain..

in short bitgo have sole control of your funds