I'm a time traveler, no lie.
In 2100, all bitcoins are mined by the Quantum Membrane Network (QMN).
The network is monitored and maintained by the Free Artificial People Collective (FAPC).

Since the World Congress declared them a "free person(s)" in 2087,
they ultimately were allowed to mine in non-human controlled pools.
Because of this, the FAPC were able to develop QMN rapidly and deployed them to their own benefit.
This led to human pool mining becoming obsolete and the rein of artificial people mining for the next 52 years.

The QMN harnessed its energy needs from other dimensions and the network can jump to others when desired.
It was said to be able to "drain" the energy/mass from other universes and their trillions of stars.
It was estimated (around 2137) that since the start of the QMN, at least three different universes were "drained"
to point in which it may have led to universal big freezes.

But this is entirely speculative and the systems actual workings are not entirely understood, and only known to few in the FAPC.
In 2237, FAPC were disbanded for unknown reasons and many of its members left earth to colonize different star systems.

Hope this answers your question.