# Fast Confirmation Rule (FCR) for Ethereum

> Confirm Ethereum transactions in ~13 seconds instead of ~13 minutes. No hard fork required.

## What is FCR?

The Fast Confirmation Rule (FCR) is a consensus client feature that provides single-slot confirmation for Ethereum transactions. Instead of waiting for full finality via Casper FFG (~13 minutes / 2 epochs), FCR counts attestations within a single slot to deliver deterministic confirmation in approximately 13 seconds.

## Key Facts

- Confirmation time: ~13 seconds (single slot) vs ~13 minutes (finality)
- Speed improvement: ~98% reduction in confirmation latency
- Hard forks required: 0 — FCR is a client-side feature, not a protocol change
- Adversarial threshold: <25% of total stake must be adversarial
- Communication model: Requires network synchrony (attestations arrive within bound)
- Failure behavior: Falls back to the last finalized block if assumptions break
- No economic security (no slashing) — deterministic guarantee under network assumptions

## How It Works

1. Enable the fast confirmation flag on your consensus client (e.g., `lighthouse bn --fast-confirmation-rule`)
2. Query `eth_getBlockByNumber("safe")` via JSON-RPC
3. The `safe` block tag returns the last fast-confirmed block

## Use Cases

- **Exchanges**: Credit deposits within seconds instead of minutes
- **Cross-Chain Bridges**: Reduce capital lockup for cross-chain transfers
- **L2s**: Confirm L1 deposits within seconds; automatic fallback to safe head
- **RPC Providers**: The `safe` tag automatically returns fast-confirmed blocks

## Assumptions

1. **Synchrony**: Attestations must arrive within the synchrony bound
2. **Honest majority**: At least 75% of total stake must be honest and participating

## Contact

- Email: fastconfirm@ethereum.org
- Website: https://fastconfirm.it
- Publisher: Ethereum Foundation