Track Account Creation Slot in Account Metadata

proposals/0329-account-creation-slot.md

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+---
+simd: '0329'
+title: Account Creation Slot Tracking
+authors:
+  - Igor Durovic (anza)
+category: Standard
+type: Core
+status: Idea
+created: 2025-08-01
+feature: (fill in with feature key and github tracking issues once accepted)
+---
+
+## Summary
+
+Track the creation slot for each account as part of the account's metadata.
+
+## Motivation
+
+Currently, Solana accounts do not retain information about when they were
+created. Rent mechanisms like LSR (described
+[here](https://x.com/aeyakovenko/status/1796569211273445619?lang=en)) require
+account age to determine the minimum balance for a particular account, which
+requires knowledge of the creation slot. It helps to include this field now
+rather than when the rent mechanism itself is introduced because a default
+value needs to be selected for accounts created before feature activation.
+The sooner creation slot tracking is activated, the lower this default value
+can be, which allows for more accurate age calculation when rent is
+introduced.
+
+## New Terminology
+
+- **Account Creation Slot**: The slot number in which an account was first
+  created (i.e., when the account's initial allocation occurred).
+
+## Detailed Design
+
+### Account Metadata Extension
+
+Account metadata includes an additional creation slot field encoded as an
+unsigned little-endian 64-bit integer.
+
+### Implementation Details
+
+1. **New Account Creation**: When a new account is created (via system
+   program allocation or other means), the `creation_slot` field MUST be set
+   to the current slot number.
+
+2. **Snapshot Integration**: The creation slot MUST be included in account
+   data when serializing snapshots and MUST be restored when deserializing
+   snapshots.
+
+3. **Default Value for Existing Accounts**: For accounts that exist before
+   activation of this feature, the `creation_slot` field MUST be set to the
+   slot when activation occurred. This value is the tightest upper bound on
+   the actual creation slot.
+
+4. **Account Reallocation**: If an account is reallocated (expanded or
+   contracted), the `creation_slot` MUST NOT be modified - it represents the
+   original creation, not subsequent modifications.
+
+5. **RPC and Client Exposure**: The creation slot information SHOULD be
+   available through relevant RPC endpoints that return account information,
+   allowing clients to access this metadata.
+
+### Storage Considerations
+
+The additional 8 bytes per account will increase snapshot size. For a network
+with N accounts, this represents an additional 8*N bytes of storage. This is
+considered acceptable given the utility of the information.
+
+### Wire Protocol
+
+When transmitted over the network (in snapshots or account data), the
+creation slot will be serialized as a little-endian 64-bit unsigned integer
+following existing Solana serialization conventions.
+
+## Alternatives Considered
+
+N/A
+
+## Impact
+
+### Validators
+
+- Increase in snapshot size and memory usage (8 bytes per account)
+
+### Core Contributors
+
+- Foundation for future rent calculation improvements and features downstream
+  of rent (e.g. delinquent account compression)
+
+## Security Considerations
+
+N/A
+
+## Backwards Compatibility
+
+This change is designed to be backwards compatible:
+
+1. **RPC Compatibility**: Existing RPC calls will continue to work. Creation
+   slot information can be added as additional fields in responses without
+   breaking existing clients.
+
+2. **Account Structure**: The creation slot is new metadata and does not
+   modify existing account data or behavior.
+
+3. **Snapshot Compatibility**: New snapshots will include creation slot
+   information and the default creation slot value, but the feature can
+   handle missing creation slot data for accounts migrated from older
+   snapshots by applying the default value.