WWDC 2025 - Discover Metal 4

Apple has unveiled Metal 4, a revolutionary update to their low-level graphics and compute API that promises to unlock the full performance potential of Apple Silicon. After powering complex applications like Cyberpunk 2077 and professional apps for over a decade, Metal 4 represents the next evolutionary step for developers building demanding games and applications.

What's New in Metal 4?

Metal 4 introduces fundamental changes across five key areas:

• Command Structure: Entirely new command encoding with explicit memory management
• Resource Management: Richer, more complex visual capabilities
• Shader Compilation: Faster compilation with reduced redundancy
• Machine Learning Integration: Seamless ML integration throughout your Metal app
• MetalFX Enhancements: Built-in performance boosting solutions

Device Compatibility

Metal 4 is supported on:

• Mac: Apple M1 and later chips
• iOS/iPadOS: A14 Bionic and later chips
• Uses the same Metal framework you may already have in your app

🔧 Command Encoding Revolution

The New Command Structure

Metal 4 introduces a completely redesigned command system that's both familiar and more powerful:

Traditional Metal Flow:

Metal Device → Command Queue → Command Buffer → Command Encoder

Metal 4 Enhanced Flow:

Metal Device → MTL4CommandQueue → MTL4CommandBuffer → Unified Encoders

Key Changes:

1. MTL4CommandQueue: New queue type obtained from Metal device
2. MTL4CommandBuffer: Decoupled from queues, enabling parallel encoding
3. Unified Command Encoders: Consolidation of multiple encoder types
4. MTL4RenderCommandEncoder: Features attachment mapping for efficient render target swapping

Unified Command Encoder Revolution

One of Metal 4's biggest improvements is the consolidation of command encoders. Instead of managing multiple separate encoders, Metal 4 introduces:

MTL4ComputeCommandEncoder - The new unified encoder that handles:

• Dispatch: Compute shader operations
• Blit: Memory copy and image processing operations
• Acceleration Structure: Ray tracing acceleration structure building

This unified approach means:

• Fewer encoders to manage - Reduces complexity in your rendering pipeline
• Memory savings - No need to allocate separate encoders for different operations
• Simplified workflow - One encoder handles multiple command types seamlessly

MTL4RenderCommandEncoder gets enhanced with:

• Attachment mapping - Map logical shader outputs to physical color attachments
• Dynamic attachment swapping - Change render targets on the fly without allocating new encoders
• Reduced memory overhead - Configure once, swap efficiently

Memory Management with MTL4CommandAllocator

Metal 4 introduces explicit memory management through MTL4CommandAllocator:

• Take direct control of command buffer memory usage
• Essential for maximizing system resources in modern applications
• Prevents memory waste and improves performance

Resource Management Transformation

The Evolution of Resource Usage

Modern applications have evolved from simple resource usage to complex bindless rendering:

Past: Single buffer + texture per object
Present: Hundreds of resources per scene
Metal 4 Solution: Smart resource management with argument tables

MTL4ArgumentTable

Replace traditional bind points with flexible argument tables. Metal 4 provides a new MTL4ArgumentTable type that stores the binding points your app needs. You create tables with a size based on the bind points your application requires. For bindless rendering, the argument table typically needs just one buffer binding.

Residency Sets: Unified Memory Management

Apple Silicon's unified memory requires explicit residency management. Metal 4 uses residency sets to specify resources that should be made resident and accessible to the hardware.

Key Benefits:

• Set up once at startup with all required resources
• Add to command queue once - all command buffers automatically include resources
• Background thread updates for streaming applications

Placement Sparse Resources

For applications requiring dynamic memory control, Metal 4 supports placement sparse resources. These are allocated without storage pages initially, with pages provided from a placement heap on-demand. This enables:

• Dynamic quality scaling across different devices
• Resource streaming capabilities
• Fine-grained memory allocation control

Synchronization with Barriers

Metal 4 introduces a low-overhead Barrier API for stage-to-stage synchronization. Barriers ensure that resource writes and reads occur in the correct order across different pipeline stages.

Key Pipeline Stages:

• Dispatch: Compute operations
• Fragment: Rendering operations
• Vertex: Geometry processing

The barriers work stage-to-stage, so you need to consider which stage each operation runs in. For example, a texture processing compute operation followed by a render that uses that texture would require a dispatch-to-fragment barrier.

Shader Compilation Improvements

MTL4Compiler Interface

Dedicated compilation contexts provide explicit control:

• Separate from Metal device
• Inherits thread priority for quality-of-service
• Enables scheduling improvements

Flexible Render Pipeline States

Optimize compilation for shared Metal IR:

1. Create unspecialized pipeline once
2. Specialize for different color states
3. Reuse compiled IR across pipelines

This dramatically reduces compilation time for pipelines sharing common code.

Machine Learning Integration

Metal 4 makes ML a first-class citizen with comprehensive tensor support.

Metal Tensors

Multi-dimensional data containers that extend beyond 2D:

• Native API integration
• Metal Shading Language support
• Complex indexing handled automatically

Two Integration Approaches:

1. Machine Learning Command Encoder

• For large-scale networks
• Command-level interleaving with graphics
• Compatible with CoreML package format

2. Shader-Embedded ML

• For smaller networks
• Direct integration into shader pipelines
• Uses Metal Performance Primitives
• Optimized tensor operations

Neural Material Evaluation Workflow

Traditional approach requires multiple pipeline stages:

1. Sample latent textures
2. Create input tensors
3. Perform inference
4. Use output for shading

Metal 4 approach combines these into a single shader dispatch, allowing operations to share thread memory for better performance. This eliminates the need to sync tensors from device memory between each step.

MetalFX Enhancements

New Features:

1. Frame Interpolation: Generate intermediate frames for higher refresh rates
2. Denoising: Remove noise from ray-traced images during upscaling
3. Enhanced Upscaling: Render low-resolution, upscale for performance

Performance Benefits:

• Reduced GPU time per frame
• Higher refresh rates without quality loss
• Perfect for high-resolution displays

📈 Adoption Strategy

Phase 1: Compilation

• Easiest starting point
• Integrate MTL4Compiler for quality-of-service improvements
• Add flexible render pipelines

Phase 2: Command Encoding

• Adopt new command generation model
• Leverage parallel encoding
• Integrate machine learning capabilities

Phase 3: Resource Management

• Implement residency sets (easy win)
• Add barriers for synchronization
• Consider placement sparse for streaming

Gradual Migration Approach

Metal 4 allows gradual adoption where you can mix traditional Metal command queues with MTL4CommandQueues. For placement sparse resources, you can use Metal events to synchronize work between the queues:

1. Traditional Metal queue continues existing render work
2. MTL4CommandQueue handles placement sparse mapping operations
3. Metal events coordinate between the two queues
4. Submit non-dependent work first to keep hardware fully utilized

Developer Tools Support

Metal 4 comes with full tooling support:

• API and Shader Validation: Identify common problems
• Metal Debugger: Deep dive into Metal 4 usage
• Metal Performance HUD: Real-time performance overlay
• Metal System Trace: Performance analysis
• Xcode 16: Built-in Metal 4 project template

Key Takeaways

Remember the "5 Pillars" of Metal 4:

1. Command Encoding: New unified structure with explicit memory management
2. Resource Management: Argument tables, residency sets, and sparse resources
3. Synchronization: Low-overhead barriers for stage coordination
4. Compilation: Flexible pipelines and improved shader compilation
5. Machine Learning: First-class tensor support and seamless integration

Performance Wins:

• Parallel encoding across command buffer types
• Reduced compilation time through flexible pipelines
• Efficient memory usage with explicit management
• ML acceleration with optimized tensor operations
• Higher frame rates through MetalFX improvements

Getting Started

1. Download: Available in the upcoming developer beta
2. Sample Code: Available now on Apple Developer
3. Xcode Template: Create new project → Game → Metal 4
4. Documentation: Full documentation on Apple Developer website

Metal 4 represents a significant leap forward in graphics and compute capabilities, designed specifically for the next generation of games and professional applications. With its modular adoption approach, you can integrate new features where they provide the most benefit to your specific use case.

The future of high-performance graphics on Apple platforms starts with Metal 4 – and that future is available today.