Hyperparameters

kappa

Majority-stake threshold at which a weight counts as consensus-supported in Yuma Consensus.

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kappa is the majority-stake threshold of Yuma Consensus: the fraction of active stake that must support a weight level for it to count as consensus. It shapes how much a stake majority can discipline outlier validators, so validators and subnet designers both care — but only root governance can change it.

How it works

Each epoch, the chain computes a per-miner consensus score as a stake-weighted median (weighted_median_col in pallets/subtensor/src/epoch/math.rs, called from epoch/run_epoch.rs with kappa as the majority ratio): the highest weight level such that validators holding at least kappa of active stake set a weight at or above it. Every weight above that consensus value is clipped down to it (inplace_col_clip), and the clipped matrix drives ranks, incentive, and validator trust. In the classic sigmoid formulation, kappa is also the midpoint of the trust curve that rho steepens.

Stored as u16 where 65535 = 1.0; the default 32767 means 0.5 — a simple stake majority. Raising it demands broader agreement before a weight survives clipping; lowering it lets smaller stake coalitions set consensus. The full pipeline is described in Yuma Consensus.

rho / kappa trust sigmoid

kappa is the midpoint of the trust sigmoid, sigmoid_safe in epoch/math.rs: trust = 1 / (1 + e^(−rho × (x − kappa))). The dashed marker is the majority threshold — alignment crossing kappa flips trust through 0.5, from mostly-distrusted to mostly-trusted. Slide kappa to move the crossing.

Trust at midpoint

0.50

always 0.5 at x = kappa

Slope at midpoint

2.50

rho / 4

kappa raw (u16)

32768

65535 = 1.0; 32767 ≈ 0.5

10
0.50

Reading and setting

Inspect with:

btcli sudo get --netuid N --name kappa

Not settable by the subnet owner — root/governance only (sudo_set_kappa in the AdminUtils pallet requires the root origin). When set, the raw value is a u16: 32767 ≈ 0.5.

rho · tempo · activity_cutoff · max_validators