KappaSet

Event Re-added v101 → v219, v233 → v265, v273 → v277, v290 → current #18

Emitted when kappa parameter is changed.

Useful for: subnet ownersvalidatorsminersanalyticsdevelopers

The Big Picture

Kappa is a consensus parameter that controls how 'strict' the consensus mechanism is. It affects how much validator agreement is required for miners to receive high scores. Higher kappa means stricter consensus - miners need more validators to agree on their quality to earn top rewards. Lower kappa is more lenient - even miners with mixed evaluations can earn well. Subnet owners tune kappa to balance between rewarding clear consensus winners vs giving more miners a chance.

Why This Matters

Kappa affects how your validator evaluations translate into miner rewards. If you're a miner, higher kappa means you need more validators to agree you're good. If you're a validator, kappa affects how much your individual evaluation matters vs the consensus.

Example Scenario

Subnet 4 has wide variance in validator evaluations - some miners rated high by some validators, low by others. The owner increases kappa to reward only miners with strong consensus. KappaSet fires with the new value. After this, miners with mixed evaluations see lower rewards while consensus favorites benefit.

Common Questions

What's a typical kappa value?: Varies widely by subnet. The parameter is scaled (often 0-65535 representing 0-1). Check your subnet's current value and documentation for what values mean in practice.
How does kappa interact with validator count?: With more validators, kappa's effect is more pronounced. High kappa with many validators creates very strict consensus. Low kappa with few validators creates very loose consensus.
Can kappa be changed frequently?: Typically rate-limited to prevent instability. Frequent kappa changes would make rewards unpredictable. Subnet owners usually set it once and adjust rarely.

Use Cases

Tune consensus sensitivity for subnet
Monitor consensus parameter changes
Analyze how kappa affects reward distribution
Model emission outcomes under different kappa values

How to Use This Event

→ Monitor kappa changes on subnets you mine on
→ Track kappa evolution to understand subnet strategy
→ Model reward impacts of kappa changes

From Chain Metadata

Kappa is set for a subnet.

Triggers

Preconditions

Caller has admin/sudo privileges
New kappa is within valid range (typically 0-65535)

Effects

Postconditions

Kappa updated for subnet
Future consensus calculations use new kappa

Side Effects

Affects consensus mechanism calculations
Changes how validator agreement translates to miner scores

Event Data

#	Name	Type	Description
0	arg0	u16	Event field #0 (u16)
1	arg1	u16	Event field #1 (u16)

Code Examples

import { ApiPromise, WsProvider } from "@polkadot/api";
import { stringCamelCase } from "@polkadot/util";

const provider = new WsProvider("wss://entrypoint-finney.opentensor.ai:443");
const api = await ApiPromise.create({ provider });

// Subscribe to KappaSet events
api.query.system.events((events) => {
  events
    .filter(({ event }) =>
      event.section === stringCamelCase("SubtensorModule") &&
      event.method === "KappaSet"
    )
    .forEach(({ event }) => {
      console.log("KappaSet:", event.data.toHuman());
    });
});

Version History

Version:

v101 block 1 2 args

v233 block 4,920,350 2 args

v273 block 5,659,032 2 args

v290 block 5,947,548 2 args Current

Runtime Info

View Source

Pallet Index: 7
Event Index: 18
First Version: v101
Current Version: v393

Back to SubtensorModule Events