Slot

Slots are the time-based unit that PoS blockchains use to coordinate block production. Each slot is a fixed length (12 seconds on Ethereum, 400ms on Solana, 1 second on most Cosmos chains) during which one specific validator has been pre-assigned the right to propose a block. If they propose a valid block on time, the slot is successful. If they’re offline or propose an invalid block, the slot is missed and the chain moves to the next slot with a different validator. Skipped slots are normal and expected.

The slot schedule is computed in advance for each epoch. At the start of an epoch, the network’s randomness source picks which validator gets each slot in that epoch, weighted by stake (validators with more stake get more slots). This gives validators time to prepare for their upcoming slots and ensures the schedule is unpredictable enough that no validator can game when they’ll be selected. The validator only knows which specific slots they have once the epoch begins.

The relationship between slots and blocks varies by chain. Most chains produce one block per slot when the assigned validator is online. Some chains have multiple proposers per slot (with various tie-breaking rules) for higher throughput. Solana’s high slot rate (400ms slots) means it produces blocks much more frequently than Ethereum, which is part of how it achieves high throughput. NEAR uses a slightly different model where multiple shards each produce chunks per slot and the chunks are aggregated into a single block.

For most users, slots are an internal implementation detail that they never need to think about. They become relevant when reading technical post-mortems about missed blocks, network outages, or validator performance issues. Validators care about their slot success rate because it directly affects their rewards: missing slots means missing rewards. The OYM project reviews of L1 chains usually note slot-level performance only when it’s anomalous; routine missed slots are background noise.