Solana Improvement Documents (SIMDs) Summary

Solana Improvement Documents (SIMDs) are formal design documents used to propose, discuss, review and track substantial changes to Solana and its development processes. 

They provide a structured way for developers and community members to examine technical changes before they are implemented or activated.

A SIMD is not automatically a live network upgrade. Proposals move through stages such as Draft, Review, Accepted, Implemented and Activated, making the status of each document important when assessing what has actually changed on Solana.

Key Takeaways

• Solana Improvement Documents provide a structured framework for documenting and reviewing substantial changes to Solana's protocol, interfaces, networking and development processes.
• A SIMD can remain a proposal for some time. Accepted, Implemented and Activated describe different points in the development lifecycle.
• Notable SIMDs have addressed areas such as account-state hashing, transaction formats and validator functionality, showing how the network's technical architecture continues to develop.

What Are Solana Improvement Documents (SIMDs)?

Solana Improvement Documents, commonly shortened to SIMDs, are design documents that describe proposed or accepted changes to Solana and its surrounding ecosystem.

The SIMD project aims to standardise high-quality documentation for Solana and track both past and ongoing improvements. SIMD-0001, titled Solana Proposal Process, establishes the framework used to develop and review proposals.

The documents are useful because protocol changes can affect several parts of the network at once. A change to transaction validity, validator behaviour, networking or an interface may require developers and other ecosystem participants to understand the proposed design before it becomes part of the network.

SIMDs therefore serve several purposes. They explain why a change is being proposed, describe how it would work, identify potential trade-offs and provide a record of the decisions surrounding the change.

They can also help developers distinguish between an idea under discussion and a feature that has already been implemented and activated.

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How Does the Solana SIMD Process Work?

The SIMD process has several stages. Understanding them is essential when reviewing a Solana Improvement Document because the status provides important context about whether a proposal is merely being considered or has already become part of the network.

Idea and Draft

The process starts with an idea. Before creating a formal proposal, the SIMD process recommends discussing and vetting the idea with the Solana community.

If the concept moves forward, it becomes a Draft. The author prepares the document using the proposal format and submits it for review.

A draft normally needs to explain the motivation behind the change, its proposed design, potential effects and relevant alternatives. The goal is to give reviewers enough information to assess the proposal rather than simply describe an intended outcome.

Review and Acceptance

The Review stage is where technical feedback becomes particularly important.

According to SIMD-0001, the proposal owner is responsible for gathering and incorporating feedback. Relevant core contributors are involved in the review, with discussions documented through the SIMD repository.

A proposal can then move to Accepted once the relevant contributors have reached sufficient agreement. Acceptance does not mean the change is already running on Solana.

This distinction is important for anyone researching Solana SIMDs. A proposal can be accepted while still waiting for development work to be completed.

Implementation and Activation

Once development teams have completed the relevant work, the proposal can reach the Implemented stage.

Activation comes later. Under the SIMD process, a proposal receives Activated status after it has been implemented, tested and activated on Solana mainnet beta.

This creates a useful distinction:

Accepted: The proposal has passed the relevant review process.

Implemented: The required development work has been completed.

Activated: The implemented and tested feature has been activated on mainnet beta.

A reader looking at a SIMD should therefore check its current status rather than assuming that an accepted proposal is already active.

Other SIMD Statuses

Not every proposal follows a straight path from Draft to Activated.

A proposal can become Living when it is designed to be continually updated rather than reach a final state. SIMD-0001 itself is classified as Living.

A proposal can become Stagnant after a prolonged period without activity. It can also be Withdrawn by its author.

These statuses help readers understand why a SIMD may appear in the repository without becoming a completed network change.

What Types of SIMDs Exist?

SIMDs are not all designed for the same type of change. The proposal process distinguishes between Standard, Meta and Advisory proposals.

Standard SIMDs

Standard proposals cover changes that affect most or all Solana implementations. They include changes involving the protocol, consensus, block or transaction validity, application standards and interoperability.

Standard SIMDs are divided into areas such as Core, Networking and Interfaces.

Core proposals cover changes affecting consensus or substantial validator behaviour.

Networking proposals address changes or substantial improvements to Solana's network protocol specifications.

Interfaces proposals cover breaking changes involving client JSON RPC API specifications and standards.

This means that a SIMD number alone does not tell readers what part of Solana is being changed. The category and type should also be checked.

Meta and Advisory Proposals

Meta SIMDs focus on processes surrounding Solana rather than directly changing the protocol itself. They can cover procedures, guidelines, decision-making processes and aspects of the development environment.

Advisory proposals provide clarifying information or notices about changes that do not require the type of protocol-breaking consensus associated with a Standard proposal.

The distinction matters because not every SIMD represents a change to validator consensus or network execution.

Notable Solana SIMDs to Know

Looking at individual proposals makes the SIMD process easier to understand. Rather than treating every SIMD as equally important, it is more useful to examine proposals that illustrate different types of technical development.

SIMD-0215: Accounts Lattice Hash

SIMD-0215, titled Homomorphic Hashing of Account State, proposes the Accounts Lattice Hash.

The proposal describes a new hash designed to maintain a hash of Solana's total account state. Its stated motivation is to make it practical to maintain an account-state hash as the network scales.

SIMD-0215 is currently marked Activated in the official repository.

The proposal is also an example of how one SIMD can provide the foundation for later changes. The Accounts Lattice Hash is referenced by subsequent proposals dealing with snapshot hashing and the removal of the Accounts Delta Hash.

SIMD-0220: Snapshots Use Accounts Lattice Hash

SIMD-0220 proposes using the Accounts Lattice Hash as the Snapshot Hash.

The proposal explains that this change replaces the previous Merkle-based account hashing calculation used in snapshots with the Accounts Lattice Hash introduced by SIMD-0215.

SIMD-0220 is marked Activated.

This example shows why related SIMDs should sometimes be reviewed together. A technical change can establish a component that later proposals use to modify another part of Solana's architecture.

SIMD-0223: Removes Accounts Delta Hash

SIMD-0223 follows the Accounts Lattice Hash work and proposes removing the Accounts Delta Hash.

The proposal argues that once the Accounts Lattice Hash is available, the Merkle-based Accounts Delta Hash becomes redundant. Its implementation also changes the bank hash and therefore affects consensus.

SIMD-0223 is marked Activated.

Together, SIMDs 0215, 0220 and 0223 illustrate how protocol improvements can be developed across multiple related proposals rather than as a single isolated change.

SIMD-0385: Transaction V1 Format

SIMD-0385 provides a different example. Titled Transaction V1 Format, the proposal introduces a new transaction format intended to address limitations in the existing legacy and v0 transaction formats.

The proposed format includes a different approach to transaction configuration and is designed to support larger transaction sizes while changing how certain transaction parameters are represented.

The proposal is currently marked Review, which makes it particularly useful when explaining the difference between a proposal and an activated network change.

A proposal can contain detailed technical specifications without necessarily being part of the live Solana protocol. Its status remains an essential part of interpreting the document.

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Why Do SIMDs Matter for Solana?

SIMDs matter because protocol development can involve complex technical trade-offs that affect validators, developers and applications.

A formal proposal gives participants a common document to examine. Instead of discussing a potential upgrade only through short announcements or informal conversations, the SIMD process creates a more detailed record of the motivation, design and expected impact.

The process also improves transparency. Developers can see why a change was proposed, reviewers can raise technical concerns, and future contributors can refer back to previous design decisions.

For validators and developers, the documents can provide an early indication of changes that may require software updates or ecosystem adjustments.

For SOL users and researchers, SIMDs provide another way to understand how Solana is developing beneath the surface. However, readers should avoid treating every proposal as a guaranteed future upgrade.

A proposal describes an intended change. Its eventual implementation depends on technical review, development, testing and activation.

How to Read a Solana SIMD

Readers do not need to understand every technical detail to review a Solana Improvement Document effectively.

Start with the SIMD number and title. These identify the proposal and provide its basic subject.

Next, check the category, type and status. These indicate what part of Solana the proposal concerns and how far it has progressed.

The Summary provides a short explanation of the proposed change, while the Motivation explains why the author believes the change is needed.

The Detailed Design is useful for readers who want to understand how the proposal would work technically.

The Impact section can help identify which parts of the ecosystem could be affected. Security considerations and backwards compatibility are also important when evaluating a protocol change.

Finally, always check the proposal's current status. A SIMD marked Review should not be described in the same way as one marked Activated.

Conclusion

Solana Improvement Documents provide a structured way to understand how significant changes to Solana are proposed, reviewed and introduced. They cover areas ranging from validator and consensus changes to networking, interfaces and development processes.

The most important point when reviewing a Solana SIMD is its status. A proposal in Draft or Review represents an idea under development, while Accepted, Implemented and Activated describe progressively later stages. 

By checking the proposal's category, technical design and current status, readers can distinguish between proposed changes and features that have actually reached the network.

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FAQ

What does SIMD mean in Solana?

SIMD stands for Solana Improvement Document. It is a formal document used to describe and review proposed or accepted changes involving Solana and its development processes.

What is the purpose of a Solana Improvement Document?

A SIMD provides a structured record of a proposed change, including its motivation, design, potential impact and relevant trade-offs. It also creates a framework for technical review.

How does a Solana SIMD become activated?

A proposal generally moves from Idea to Draft, Review and Accepted before implementation. It can then become Implemented once development is complete and Activated after testing and activation on Solana mainnet beta.

Are all Solana SIMDs implemented?

No. SIMDs can remain in Review, become Stagnant or be Withdrawn. Even an Accepted proposal is not necessarily an implemented or activated feature.

Where can I review Solana SIMDs?

Solana Improvement Documents are maintained in the official SIMD repository, where readers can review individual proposals, their technical details and their current statuses.

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