On-chain as far as I remember, but the Foundation still has a lot of sway over protocol changes so the line between "decentralized" and "whatever they decide" can get blurry fast.

That blurriness exists at the governance layer, not the reward distribution layer, the actual payout mechanics are baked into consensus and the Foundation can't just redirect node rewards without a hard fork that the whole network has to accept.

Sia actually has a habit of consolidating rather than bleeding when the move is tied to genuine network activity, and if storage demand is picking up, that changes the dynamic compared to a pure speculation pump.

Said the same thing last time it popped and then watched it slide 20%.