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Metal Flash Attention

Metal Flash Attention is an MIT-licensed Swift library that ports FlashAttention to Apple silicon using Metal, with single-headed attention kernels compiled at runtime through JIT.

Explore the practical guide ↓

Independent OpenViST project profile, based on linked sources.

Metal Flash Attention — OpenViST project profile in AI Developer Tools & SDKs.
OpenViST project illustration. See the linked sources for product details.
Understand the project

Practical overview

When it fits

Use it when developing or examining single-headed FlashAttention kernels for Apple silicon, especially when exploring Metal performance constraints or adapting the source.

Who it is for

  • Developers studying attention-kernel bottlenecks on Apple silicon.
  • Swift and Metal developers experimenting with attention algorithms and kernel modifications.

Documented uses

  • Build and run the library’s documented test suite.
  • Inspect a test’s console output through an Xcode project workflow.
  • Study the implementation’s handling of register pressure, parallelism, and backward-pass memory use.
  • Use the source as a starting point for documented kernel customizations such as multi-head, mask, or block-sparse support.
Before you choose

Requirements & limits

The repository is public on GitHub and identifies its license as MIT. The README documents macOS package build and test commands.

  • The implementation is limited to single-headed attention; multi-head and mask support are described as possible code modifications.
  • Its backward pass uses more computation while reducing memory relative to the referenced FlashAttention implementation.
  • The README measures performance in gigainstructions per second and cautions that its model has limits, including at small head dimensions on M3-generation hardware.
  • The documented macOS build uses -Xswiftc -Ounchecked for performance-sensitive CPU code.

Check current requirements in the official documentation. Source-based guidance does not mean OpenViST has run or independently tested this project.

Source-based practical guide

Build and test the Swift package

Compile the repository and run its documented test suite on macOS.

Before you start

  • macOS
  • Swift package workflow
  • The metal-flash-attention repository

Steps

  1. Clone the repository with the command below.

    Documented command
    git clone https://github.com/philipturner/metal-flash-attention

  2. Build it with swift build -Xswiftc -Ounchecked.

  3. Run the tests with swift test -Xswiftc -Ounchecked.

Expected outcome

The package is built and the repository’s test suite is run.

Guide limitations

  • The documented commands describe a macOS workflow; they do not establish compatibility with other environments.
  • The README’s expected test duration is guidance, not a test result verified here.
Documentation 1 ↗
Source-based practical guide

Bring a repository test into an Xcode project

Set up a documented Xcode workflow that invokes a repository test and displays console output.

Before you start

  • Xcode project using the SwiftUI template
  • The repository added as a Swift package dependency
  • A function that invokes a selected test and returns a String

Steps

  1. Set the Swift compiler optimization option to -Ounchecked in the project’s build settings.

  2. Add the repository as a Swift package dependency.

  3. Choose a test under Tests/FlashAttention and copy its raw source into the project.

  4. Invoke the test from the function and inspect the Xcode console output.

Expected outcome

The selected test is invoked through the documented project workflow, with output available in the Xcode console.

Guide limitations

  • The README describes this as a developer feedback workflow; it does not document a general application integration interface.
  • The workflow’s compatibility with both macOS and iOS is stated in the README, not independently verified here.
Documentation 1 ↗
Evidence and transparency

Sources & review

Official repository ↗
Source record details
Source availability
Active
Sources checked
14 October 2026
Original website title
philipturner/metal-flash-attention · Official homepage title · retained in its source language
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