# immunity_period (/docs/hyperparameters/immunity-period)

`immunity_period` is the number of blocks a freshly registered neuron cannot be pruned to make room for a new registration. Subnet owners tune it to give new miners time to earn emission before they compete for their slot; miners care because it is their grace window to prove themselves.

## How it works [#how-it-works]

When a subnet is at [`max_allowed_uids`](/docs/hyperparameters/max-allowed-uids), each new registration must recycle an existing slot. `get_neuron_to_prune` (`pallets/subtensor/src/subnets/registration.rs`) scans every UID and treats a neuron as immune while `current_block − registration_block` is less than `immunity_period`. It picks the lowest-emission non-immune neuron (ties broken by older registration, then lower UID). Owner-immune UIDs (see [`owner_immune_neuron_limit`](/docs/hyperparameters/owner-immune-neuron-limit)) are skipped entirely.

Immunity is not absolute: if pruning a non-immune neuron would leave `MinNonImmuneUids` (default 10) or fewer non-immune UIDs, the chain instead prunes the lowest-emission immune neuron. If no candidate exists at all, registration fails with `NoNeuronIdAvailable`.

The default is 4096 blocks, about 13.7 hours at 12-second blocks. Longer periods shelter newcomers but shrink the pool of prunable slots; with heavy registration churn, most of the subnet can end up immune.

<HyperparamUidLifecycle focus="immunity_period" />

## Reading and setting [#reading-and-setting]

```
btcli sudo get --netuid N --name immunity_period
```

The value is a plain block count:

```
btcli sudo set --netuid N --name immunity_period --value 4096
```

## Related [#related]

[`max_allowed_uids`](/docs/hyperparameters/max-allowed-uids), [`owner_immune_neuron_limit`](/docs/hyperparameters/owner-immune-neuron-limit), [`serving_rate_limit`](/docs/hyperparameters/serving-rate-limit), [`min_burn`](/docs/hyperparameters/min-burn), [`max_regs_per_block`](/docs/hyperparameters/max-regs-per-block)