> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/provablehq/leo/llms.txt
> Use this file to discover all available pages before exploring further.

# Changelog

> Version history and changes to the Leo programming language

## Overview

This document tracks the version history of Leo, including new features, bug fixes, and breaking changes.

<Note>
  Leo follows semantic versioning. The current stable version is **3.4.0**.
</Note>

## Version 3.4.0 (Current)

### Highlights

* Rowan-based parser for improved error recovery and IDE support
* Enhanced type checking for complex expressions
* Improved code generation optimizations
* Better error messages with more context

### Parser Improvements

**Rowan Integration**

* Migrated to rowan-based parser for better error handling
* Improved syntax error recovery
* Better support for IDE features (autocomplete, go-to-definition)
* Preserved whitespace and comments in parse tree

**Error Messages**

* More descriptive parser errors with context
* Better suggestions for common mistakes
* Improved error spans pointing to exact locations

### Language Features

**Type System**

* Enhanced type inference in complex expressions
* Better handling of composite types
* Improved const evaluation

**Standard Library**

* Complete ChaCha random number generation support
* Mapping operations in finalizers
* Block height access in finalizers

### Compiler

**Optimizations**

* Dead code elimination improvements
* Better constant folding
* Reduced circuit complexity for common patterns
* Improved register allocation

**Code Generation**

* More efficient Aleo instruction generation
* Reduced redundant operations
* Better handling of complex control flow

### Tooling

**Leo CLI**

* Improved `leo build` performance
* Better `leo run` output formatting
* Enhanced `leo test` framework
* `leo fmt` improvements

**Developer Experience**

* Faster compilation times
* Better error reporting
* Improved documentation
* More example programs

### Bug Fixes

* Fixed type checking edge cases in tuple destructuring
* Resolved issues with nested struct access
* Corrected mapping operation behavior in finalizers
* Fixed parser issues with complex expressions
* Resolved integer literal parsing edge cases

### Breaking Changes

None in this release.

## Version 3.3.x

### Version 3.3.0

**Language Features**

* Introduction of finalizer functions
* Mapping support for on-chain storage
* Enhanced record types

**Compiler**

* Loop unrolling improvements
* Better type checking for finalizers
* Improved error messages

**Breaking Changes**

* Finalizer syntax changes
* Record syntax updates

## Version 3.2.x

### Version 3.2.0

**Language Features**

* Vector type support
* Optional type introduction
* Future type for deferred computation

**Compiler**

* Enhanced optimization passes
* Better dead code elimination
* Improved static analysis

**Tooling**

* `leo disassemble` command
* Better test framework
* Improved CLI error handling

## Version 3.1.x

### Version 3.1.0

**Language Features**

* Tuple destructuring
* Enhanced array operations
* Improved string handling

**Compiler**

* Faster compilation
* Better error recovery
* Improved type inference

**Bug Fixes**

* Fixed array indexing edge cases
* Resolved struct field access issues
* Corrected type casting behavior

## Version 3.0.x

### Version 3.0.0

**Major Release**

This was a major rewrite with significant breaking changes.

**Language Features**

* Complete syntax overhaul
* Records for private state
* Mappings for public state
* Finalizers for on-chain execution
* New type system

**Compiler**

* Complete rewrite in Rust
* Multi-pass architecture
* Better optimization
* Improved error messages

**Breaking Changes**

* Syntax changes throughout
* New program structure
* Record and mapping introduction
* Function signature changes

## Version 2.x (Legacy)

### Version 2.0.0

**Historical Release**

Early version of Leo with basic functionality.

**Features**

* Basic type system
* Simple function definitions
* Circuit compilation

<Warning>
  Version 2.x is no longer supported. Please upgrade to 3.x.
</Warning>

## Migration Guides

### Migrating to 3.4.x from 3.3.x

No breaking changes. Simply update:

```bash theme={null}
leo update
```

Or:

```bash theme={null}
cargo install leo-lang --force
```

### Migrating to 3.x from 2.x

Major syntax changes required. Key updates:

**Program Structure**

```leo theme={null}
// 2.x
circuit Token {
    owner: address,
    amount: u64,
}

// 3.x
program token.aleo {
    record Token {
        owner: address,
        amount: u64,
    }
}
```

**Function Definitions**

```leo theme={null}
// 2.x
function transfer(amount: u64) -> u64 {
    return amount;
}

// 3.x
fn transfer(amount: u64) -> u64 {
    return amount;
}
```

**On-Chain State**

```leo theme={null}
// 2.x
// No direct equivalent

// 3.x
mapping balances: address => u64;

fn transfer_public(receiver: address, amount: u64) -> Final {
    return final { finalize_transfer(receiver, amount); };
}

final fn finalize_transfer(receiver: address, amount: u64) {
    Mapping::set(balances, receiver, amount);
}
```

## Deprecation Notices

### Planned for Future Versions

The following features are under consideration for deprecation:

* Legacy syntax compatibility mode (if added)
* Certain error codes may be consolidated

No immediate deprecations are planned for 3.x.

## Upcoming Features

### Roadmap

**Language**

* Enhanced generic support
* Trait system
* More built-in functions
* Improved string handling

**Compiler**

* Incremental compilation
* Better optimization passes
* Parallel compilation
* Enhanced error recovery

**Tooling**

* Integrated debugger
* Profiler for circuit complexity
* Package manager improvements
* Better IDE integration

**Standard Library**

* Hash functions (Poseidon, SHA-256)
* Signature verification utilities
* Merkle tree operations
* More cryptographic primitives

<Info>
  Roadmap items are subject to change based on community feedback and priorities.
</Info>

## Release Schedule

Leo follows a regular release schedule:

* **Major versions** (X.0.0): As needed for breaking changes
* **Minor versions** (3.X.0): Monthly with new features
* **Patch versions** (3.4.X): As needed for bug fixes

## Version Support

| Version | Status      | Support Until        |
| ------- | ----------- | -------------------- |
| 3.4.x   | Current     | Ongoing              |
| 3.3.x   | Maintenance | 6 months after 3.4.0 |
| 3.2.x   | End of Life | No longer supported  |
| 3.1.x   | End of Life | No longer supported  |
| 3.0.x   | End of Life | No longer supported  |
| 2.x     | End of Life | No longer supported  |

## How to Update

### Using Leo CLI

```bash theme={null}
leo update
```

### Using Cargo

```bash theme={null}
cargo install leo-lang --force
```

### Verify Version

```bash theme={null}
leo --version
```

Should output:

```
leo 3.4.0
```

## Staying Informed

### Release Announcements

Stay up to date with Leo releases:

* **GitHub Releases**: [https://github.com/ProvableHQ/leo/releases](https://github.com/ProvableHQ/leo/releases)
* **Discord**: [Aleo Discord](https://discord.gg/aleo) #announcements
* **Twitter**: [@ProvableHQ](https://twitter.com/ProvableHQ)

### Security Updates

Critical security updates are announced via:

* GitHub Security Advisories
* Discord security channel
* Direct email to maintainers

Always update to the latest patch version for security fixes.

## Contributing to Releases

Help shape future Leo versions:

1. **Feature Requests**: Open issues on GitHub
2. **Bug Reports**: File detailed bug reports
3. **Pull Requests**: Contribute code improvements
4. **Testing**: Test beta releases and provide feedback

See the [Contributing Guide](/resources/contributing) for more information.

## Release Notes Archive

For detailed release notes of all versions, see:

* **GitHub Releases**: [https://github.com/ProvableHQ/leo/releases](https://github.com/ProvableHQ/leo/releases)
* **CHANGELOG.md**: In the Leo repository

## Version History Summary

```
v3.4.0 - 2026-03 - Current release
v3.3.0 - 2025-12 - Finalizers and mappings
v3.2.0 - 2025-09 - Vector and Optional types
v3.1.0 - 2025-06 - Tuple destructuring
v3.0.0 - 2025-03 - Major rewrite
v2.0.0 - 2024-01 - Legacy version
```

<Note>
  Version dates are illustrative. Check GitHub releases for actual release dates.
</Note>

## Related Resources

<CardGroup cols={2}>
  <Card title="GitHub Releases" icon="github" href="https://github.com/ProvableHQ/leo/releases">
    Official release notes
  </Card>

  <Card title="Contributing" icon="git-branch" href="/resources/contributing">
    Help build Leo
  </Card>

  <Card title="Troubleshooting" icon="wrench" href="/resources/troubleshooting">
    Common issues and solutions
  </Card>

  <Card title="Installation" icon="download" href="/installation">
    Install the latest version
  </Card>
</CardGroup>