SIMD 0301: Remove BankHash From Votes

proposals/0301-remove-bank-hash-from-votes.md

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+---
+simd: "0301"
+title: Remove BankHash from Votes
+authors:
+  - Max Resnick (Anza)
+category: Standard
+type: Core
+status: Draft
+created: 2025-06-10
+feature: (fill in with feature key and github tracking issues once accepted)
+supersedes: (optional - fill this in if the SIMD supersedes a previous SIMD)
+superseded-by:
+  (optional - fill this in if the SIMD is superseded by a subsequent SIMD)
+extends:
+  (optional - fill this in if the SIMD extends the design of a previous SIMD)
+---
+
+## Summary
+
+This proposal would remove BankHash from votes on Solana to allow voting before
+replay is complete. If all the prerequisites are satisfied before Alpenglow is
+ready to rollout then it can be activated with Alpenglow. Otherwise it must be a
+feature flag.
+
+This is a very long line of text that should be wrapped by Prettier at eighty
+characters if proseWrap is set to always and printWidth is set to eighty.
+
+## Motivation
+
+Currently, votes include the BankHash, which ties votes to a fully executed bank
+state. Removing BankHash from votes allows validators to vote before execution
+completes. This is also called Asynchronous Execution.
+
+The synchronous confirmation flow after Alpenglow looks like this:
+
+```text
+| ----- leader broadcasts the block through rotor -------|
+        |------------------ validator recieves block ------------|       |-- validator broadcasts votes--| <-  certificate is formed
+              |--------------- validator executes block -----------------|
+```
+
+After this feature flag activates validators will be able to vote before they
+finish executing the block:
+
+```text
+| ----- leader broadcasts the block through rotor -------|
+        |------------------ validator recieves block ------------||-- validator broadcasts votes--| <-  certificate is formed
+              |--------------- validator executes block -----------------|
+```
+
+## Detailed Design
+
+This proposal contains a single change:
+
+1. Remove BankHash from votes. Validators will no longer include the BankHash in
+   their vote messages.
+
+## Dependencies
+
+| SIMD Number                                                                             | Description                                 | Status    |
+| --------------------------------------------------------------------------------------- | ------------------------------------------- | --------- |
+| [SIMD-0159](https://github.com/solana-foundation/solana-improvement-documents/pull/159) | Pre-compile Instruction Verification        | Activated |
+| [SIMD-0191](https://github.com/solana-foundation/solana-improvement-documents/pull/191) | Loaded Data Size and Program Account Checks | Activated |
+| [SIMD-0192](https://github.com/solana-foundation/solana-improvement-documents/pull/192) | Address Lookup Table Relaxation             | Review    |
+| [SIMD-0290](https://github.com/solana-foundation/solana-improvement-documents/pull/290) | Fee-payer Account Relaxation                | Review    |
+| [SIMD-0295](https://github.com/solana-foundation/solana-improvement-documents/pull/295) | Relax CU limit overage                      | Review    |
+| [SIMD-0297](https://github.com/solana-foundation/solana-improvement-documents/pull/297) | Durable Nonce Relaxation                    | Review    |
+| [SIMD-0298](https://github.com/solana-foundation/solana-improvement-documents/pull/298) | Add BankHash to Block Header                | Review    |
+
+## Impact
+
+This change is not expected to have any direct impact on app developers. It is a
+consensus-breaking change and will require all validators to update their
+software to the new vote structure. Validators running older versions will be
+unable to participate in consensus once the feature flag is activated.
+
+## Security Considerations
+
+Removing BankHash from votes does not introduce new security risks by itself
+when coupled with SIMD-0298 which adds the BankHash of the parent to each block,
+because the BankHash is still part of consensus.
+
+## Drawbacks
+
+## Backwards Compatibility
+
+Either the prerequisites are all satisfied by the time Alpenglow is ready, in
+which case we can just launch alpenglow votes without the BankHash in them, or
+we will need a feature flag.
+
+This proposal requires a breaking change to the vote structure. All validators
+must implement the new vote format. The change will be gated behind a feature
+flag and activated in a coordinated manner. Validators running older versions
+will be unable to participate in consensus once the feature flag is activated.
+
+This is a very long line of text that should be wrapped by Prettier at eighty
+characters if proseWrap is set to always and printWidth is set to eighty.