Neurons are server nodes in each subnet. To become a validator or miner on a subnet you must register a neuron.

Neuron Registration

To obtain a UID (unique slot number for a neuron) on a particular subnet you must register your hotkey. The cost of the slot is variable and can be found using the command line btcli subnets list. The recycle cost is the cost to register a neuron).

The number of registrations per epoch is defined in the subnet parameters (default: 3) and if all three slots are registered in a given epoch the cost will increase for the next epoch. If some but not all slots are filled the costs will remain the same for the next epoch. If none of the slots are registered then the cost for the next epoch will decrease.

This allows the registration costs to be defined by natural market forces of demand. A historical chart is available on the subnet's page on Taostats to see the current costs for each subnet:

All new miners & validators are placed into immunity for a preset amount of time. The immunity period can be adjusted per subnet. A miner with immunity cannot be de-registered.

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Immunity period

To retrieve the immunity period (in blocks), you can use the Bittensor CLI to select a Subnet. The output includes the immunity_period. For subnet 1, it is 7200 blocks:

btcli sudo get
Enter netuid [0/1/2/3/4/5/6/7/8/9/10/11/12/13/14/15/16/17/18/19/20/21/22/23/24/25/26/27/28/29/30/31/32] (0): 1
Bittensor Version: Current 6.6.0/Latest 6.7.0
Please update to the latest version at your earliest convenience. Run the following command to upgrade:

python -m pip install --upgrade bittensor
  Subnet Hyperparameters - NETUID: 1 - finney  
 HYPERPARAMETER            VALUE               
 rho                       10                  
 kappa                     32767               
 immunity_period           7200                
 min_allowed_weights       8                   
 max_weight_limit          455                 
 tempo                     99                  
 min_difficulty            1000000000000000000 
 max_difficulty            1000000000000000000 
 weights_version           10000               
 weights_rate_limit        100                 
 adjustment_interval       112                 
 activity_cutoff           5000                
 registration_allowed      True                
 target_regs_per_interval  2                   
 min_burn                  50000000            
 max_burn                  100000000000        
 bonds_moving_avg          900000              
 max_regs_per_block        1                   
 serving_rate_limit        10                  
 max_validators            128         

Recycling of Fees

Any tao spent on registration is recycled - it is returned to the unissued supply (thus slowly lengthening the time until the next halvening). The tao recycled for registration is NOT returned to the miner upon de-registration and is considered part of the operational costs to be factored into the profitability calculations when mining.

Registration Cost

Registration cost is based on the demand, the more registrations, the higher the cost. In the parameters above, the min/max burn denotes the range of the registration cost in 1e-9 tao (rao).

Neuron De-registration

When a new miner/validator registers their hotkey, the neuron/node with the lowest emissions ranking in the subnet is de-registered.

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Miners & validators that have immunity cannot be de-registered.

If your subnet is deregistered for a new subnet, all neurons are de-registered.