collateral_drain_ratio

collateral_drain_ratio (call it k) sets how fast a hotkey earns back the collateral locked at registration when the subnet uses a nonzero collateral_lock_share. Operators care because lock / k is the total emission (miner incentive and validator dividends) they must earn before their collateral is fully withdrawable; owners tune it to control how long hotkeys stay collateralized — the security parameter for subnets whose scoring can be gamed on short horizons.

How it works

Each tempo, when hotkey emission is credited (distribute_dividends_and_incentives in pallets/subtensor/src/coinbase/run_coinbase.rs), settle_miner_collateral releases

released = min(locked − min_locked, k × emission)

from the hotkey's lock back to withdrawable stake, where min_locked is the optional self-maintained floor (zero unless set via set_min_collateral; while the lock is under the floor, emission is captured into the lock instead). The release is keyed to the registered hotkey even when miner incentive is redirected by auto-stake. At k = 1 (the default) collateral releases one-for-one with earned emission; at k = 0.5 a hotkey must earn two alpha per alpha released; at k = 2 half the lock's worth of emission releases all of it.

The subnet value is stored in CollateralDrainRatio as a U64F64 fixed-point number, but each miner's effective ratio is snapshot into their collateral entry at registration (MinerCollateralState): owner changes apply to future registrations only and can never slow (or speed) the drain of standing collateral. The owner-set extrinsic (sudo_set_collateral_drain_ratio in pallets/admin-utils/src/lib.rs) requires 0 < k ≤ 10 (MaxCollateralDrainRatio); out-of-range values fail with CollateralDrainRatioOutOfBounds. Zero is excluded by design: with no exit path for collateral, k = 0 would make the lock permanently unrecoverable — a burn with extra steps.

The deterrence math, briefly: an adversary who plans to farm emissions and abandon the hotkey must collect roughly T / (1 + k) (T = registration price) before validators stop scoring them, just to break even. Lower k raises that bar; see the worked example.

Reading and setting

btcli sudo get --netuid N --name collateral_drain_ratio

Fixed-point decimal; owner or root, rate-limited, outside the weights window:

btcli sudo set --netuid N --name collateral_drain_ratio --value 0.5

Common settings: 1.0 (default, earn-back at par), 0.2–0.5 (slow release for long-horizon or gameable-score subnets), 2.0 (fast release where the entry gate matters more than ongoing lockup).

Related

collateral_lock_share, burn_half_life, Registration collateral guide