diff --git a/.github/generate-xcode-tests-matrix.sh b/.github/generate-xcode-tests-matrix.sh
index 6eaaac9..1518707 100755
--- a/.github/generate-xcode-tests-matrix.sh
+++ b/.github/generate-xcode-tests-matrix.sh
@@ -5,8 +5,6 @@ set -e
 platforms='["macOS","iOS","tvOS","watchOS","macCatalyst","visionOS"]'
 
 includes='[
-  {"os":"macos-14", "xcode":"15.2", "swift": "5.9"},
-  {"os":"macos-14", "xcode":"15.3", "swift": "5.10"},
   {"os":"macos-15", "xcode":"16.0", "swift": "6.0"},
   {"os":"macos-15", "xcode":"16.3", "swift": "6.1"},
   {"os":"macos-26", "xcode":"26.0.1", "swift": "6.2"}
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index b33ef30..f7e1c9f 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -3,8 +3,7 @@ name: Tests
 on:
   push:
   pull_request:
-    branches:
-      - "**:**" # PRs from forks have a prefix with `owner:`
+  pull_request_target:
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
@@ -18,10 +17,6 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: "macos-14"
-            xcode: "15.1" # Swift 5.9. Same as 15.2.
-          - os: "macos-14"
-            xcode: "15.3" # Swift 5.10. Same as 15.4.
           - os: "macos-15"
             xcode: "16.0" # Swift 6.0. Same as 16.1 and 16.2.
           - os: "macos-15"
@@ -42,9 +37,9 @@ jobs:
         uses: actions/cache@v3
         with:
           path: ~/.mint
-          key: ${{ runner.os }}-mint-xcode_${{ matrix.xcode }}-${{ hashFiles('**/Mintfile') }}
+          key: ${{ runner.os }}-${{ matrix.os }}-mint-xcode_${{ matrix.xcode }}-${{ hashFiles('**/Mintfile') }}
           restore-keys: |
-            ${{ runner.os }}-mint-xcode_${{ matrix.xcode }}
+            ${{ runner.os }}-${{ matrix.os }}-mint-xcode_${{ matrix.xcode }}
 
       - run: mint bootstrap
 
@@ -52,24 +47,111 @@ jobs:
         uses: actions/cache@v3
         with:
           path: .build
-          key: ${{ runner.os }}-xcode_${{ matrix.xcode }}-swiftpm-${{ github.ref }}-${{ hashFiles('**/Package.resolved') }}
+          key: ${{ runner.os }}-${{ matrix.os }}-xcode_${{ matrix.xcode }}-swiftpm-${{ github.ref }}-${{ hashFiles('**/Package.resolved') }}
           restore-keys: |
-            ${{ runner.os }}-xcode_${{ matrix.xcode }}-swiftpm-${{ github.ref }}-
-            ${{ runner.os }}-xcode_${{ matrix.xcode }}-swiftpm-main-
-            ${{ runner.os }}-xcode_${{ matrix.xcode }}-swiftpm-
+            ${{ runner.os }}-${{ matrix.os }}-xcode_${{ matrix.xcode }}-swiftpm-${{ github.ref }}-
+            ${{ runner.os }}-${{ matrix.os }}-xcode_${{ matrix.xcode }}-swiftpm-main-
+            ${{ runner.os }}-${{ matrix.os }}-xcode_${{ matrix.xcode }}-swiftpm-
 
       - name: SwiftPM tests
-        run: swift test --enable-code-coverage | mint run xcbeautify --renderer github-actions
+        run: |
+          set -o pipefail
+          swift test --enable-code-coverage | mint run xcbeautify --renderer github-actions
+
+      - name: Convert coverage for Codecov
+        id: convert-coverage
+        uses: sersoft-gmbh/swift-coverage-action@v4
+        with:
+          ignore-conversion-failures: true
+          fail-on-empty-output: true
+
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v5
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+        with:
+          files: ${{ join(fromJSON(steps.convert-coverage.outputs.files), ',') }}
+          fail_ci_if_error: true
+
+  generate_swift_syntax_version:
+    name: Generate Swift Syntax Versions
+    runs-on: macos-26
+    outputs:
+      matrix: ${{ steps.set-matrix.outputs.matrix }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - run: brew install mint
+
+      - name: Cache Mint
+        uses: actions/cache@v3
+        with:
+          path: ~/.mint
+          key: macOS-macos-26-mint-swift-dependency-compatibility-checker
+
+      - name: Set up matrix
+        id: set-matrix
+        run: |
+          matrix="$(mint run --silent josephduffy/swift-dependency-compatibility-checker@main swift-syntax --resolve-only --github-actions-matrix)"
+          echo "${matrix}"
+          echo "matrix=${matrix}" >> "${GITHUB_OUTPUT}"
+
+  test_swift_syntax_versions:
+    name: Swift Syntax ${{ matrix.version }} Tests
+    needs:
+      - generate_swift_syntax_version
+    runs-on: macos-26
+    strategy:
+      fail-fast: false
+      matrix: ${{ fromJson(needs.generate_swift_syntax_version.outputs.matrix) }}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Select Xcode 26.0.1
+        run: sudo xcode-select --switch /Applications/Xcode_26.0.1.app
+
+      - name: Install Mint
+        run: brew install mint
+
+      - name: Cache Mint
+        uses: actions/cache@v3
+        with:
+          path: ~/.mint
+          key: macOS-macos-26-mint-xcode_26.0.1-${{ hashFiles('**/Mintfile') }}
+          restore-keys: |
+            macOS-macos-26-mint-xcode_26.0.1
+
+      - run: mint bootstrap
+
+      - run: swift package resolve
+
+      - run: swift package resolve swift-syntax --version ${{ matrix.version }}
+
+      - name: Run Tests
+        # swift-macro-testing does not compile with swift-syntax 601.0.0
+        if: ${{ matrix.version != '601.0.0' }}
+        run: |
+          set -o pipefail
+          swift test --enable-code-coverage | mint run xcbeautify --renderer github-actions
+
+      - name: Compile Project
+        if: ${{ matrix.version == '601.0.0' }}
+        run: |
+          set -o pipefail
+          swift build | mint run xcbeautify --renderer github-actions
 
       - name: Convert coverage for Codecov
         id: convert-coverage
         uses: sersoft-gmbh/swift-coverage-action@v4
+        if: ${{ matrix.version != '601.0.0' }}
         with:
           ignore-conversion-failures: true
           fail-on-empty-output: true
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v5
+        if: ${{ matrix.version != '601.0.0' }}
         env:
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
         with:
@@ -113,9 +195,9 @@ jobs:
         uses: actions/cache@v3
         with:
           path: ~/.mint
-          key: ${{ runner.os }}-mint-xcode_${{ matrix.xcode }}-${{ hashFiles('**/Mintfile') }}
+          key: ${{ runner.os }}-${{ matrix.os }}-mint-xcode_${{ matrix.xcode }}-${{ hashFiles('**/Mintfile') }}
           restore-keys: |
-            ${{ runner.os }}-mint-xcode_${{ matrix.xcode }}
+            ${{ runner.os }}-${{ matrix.os }}-mint-xcode_${{ matrix.xcode }}
 
       - run: mint bootstrap
 
@@ -123,10 +205,10 @@ jobs:
         uses: actions/cache@v3
         with:
           path: ~/Library/Developer/Xcode/DerivedData
-          key: ${{ runner.os }}-xcode_${{ matrix.xcode }}-derived_data-${{ github.ref }}
+          key: ${{ runner.os }}-${{ matrix.os }}-xcode_${{ matrix.xcode }}-derived_data-${{ github.ref }}
           restore-keys: |
-            ${{ runner.os }}-xcode_${{ matrix.xcode }}-derived_data-main
-            ${{ runner.os }}-xcode_${{ matrix.xcode }}-derived_data-
+            ${{ runner.os }}-${{ matrix.os }}-xcode_${{ matrix.xcode }}-derived_data-main
+            ${{ runner.os }}-${{ matrix.os }}-xcode_${{ matrix.xcode }}-derived_data-
 
       - name: Run Tests
         run: |
@@ -140,7 +222,7 @@ jobs:
           fail-on-empty-output: true
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v5
         env:
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
         with:
@@ -156,7 +238,7 @@ jobs:
       fail-fast: false
       matrix:
         os: ["ubuntu-latest"]
-        swift: ["5.9.2", "5.10", "6.0", "6.1", "6.2"]
+        swift: ["6.0", "6.1", "6.2"]
 
     steps:
       - uses: actions/checkout@v4
@@ -192,8 +274,8 @@ jobs:
       - name: Install Swift
         uses: compnerd/gha-setup-swift@main
         with:
-          branch: ${{ matrix.branch }}
-          tag: ${{ matrix.tag }}
+          swift-version: ${{ matrix.branch }}
+          swift-build: ${{ matrix.tag }}
 
       - name: swift test
         run: swift test
diff --git a/Mintfile b/Mintfile
index 18627cf..ec13f25 100644
--- a/Mintfile
+++ b/Mintfile
@@ -1,2 +1,2 @@
 josephduffy/xcutils@v0.3.0
-tuist/xcbeautify@1.0.1
+cpisciotta/xcbeautify@2.30.1
diff --git a/Package.swift b/Package.swift
index 4d33b48..d43f0de 100644
--- a/Package.swift
+++ b/Package.swift
@@ -19,7 +19,8 @@ let package = Package(
     ),
   ],
   dependencies: [
-    .package(url: "https://github.com/swiftlang/swift-syntax", from: "509.1.0"),
+    // Tests (specifically swift-snapshot-testing) do not support 601.0.0 but the project does build.
+    .package(url: "https://github.com/swiftlang/swift-syntax", "509.1.0"..<"603.0.0"),
     // We only really need swift-macro-testing 0.3.0 or newer but 0.4.0 is required to compile due
     // to breaking changes in swift-snapshot-testing.
     .package(url: "https://github.com/pointfreeco/swift-macro-testing.git", from: "0.4.0"),
@@ -45,12 +46,7 @@ let package = Package(
     .macro(
       name: "HashableMacroMacros",
       dependencies: [
-        .targetItem(
-            name: "HashableMacroFoundation",
-            condition: .when(
-                platforms: [.macOS, .iOS, .tvOS, .watchOS, .macCatalyst]
-            )
-        ),
+        "HashableMacroFoundation",
         .product(name: "SwiftDiagnostics", package: "swift-syntax"),
         .product(name: "SwiftSyntax", package: "swift-syntax"),
         .product(name: "SwiftSyntaxMacros", package: "swift-syntax"),
diff --git a/Package@swift-5.9.swift b/Package@swift-5.9.swift
deleted file mode 100644
index ca616c4..0000000
--- a/Package@swift-5.9.swift
+++ /dev/null
@@ -1,73 +0,0 @@
-// swift-tools-version: 5.9
-import CompilerPluginSupport
-import PackageDescription
-
-let package = Package(
-  name: "HashableMacro",
-  platforms: [
-    .macOS(.v10_15),
-    .iOS(.v13),
-    .tvOS(.v13),
-    .watchOS(.v6),
-    .macCatalyst(.v13),
-    .visionOS(.v1),
-  ],
-  products: [
-    .library(
-      name: "HashableMacro",
-      targets: ["HashableMacro"]
-    ),
-  ],
-  dependencies: [
-    .package(url: "https://github.com/swiftlang/swift-syntax", from: "509.1.0"),
-    // We only really need swift-macro-testing 0.3.0 or newer but 0.4.0 is required to compile due
-    // to breaking changes in swift-snapshot-testing.
-    .package(url: "https://github.com/pointfreeco/swift-macro-testing.git", from: "0.4.0"),
-  ],
-  targets: [
-    .target(
-        name: "HashableMacro",
-        dependencies: [
-            .targetItem(
-                name: "HashableMacroFoundation",
-                condition: .when(
-                    platforms: [.macOS, .iOS, .tvOS, .watchOS, .macCatalyst, .visionOS]
-                )
-            ),
-            "HashableMacroMacros",
-        ],
-        swiftSettings: [.enableExperimentalFeature("StrictConcurrency")]
-    ),
-    .target(
-        name: "HashableMacroFoundation",
-        swiftSettings: [.enableExperimentalFeature("StrictConcurrency")]
-    ),
-    .macro(
-      name: "HashableMacroMacros",
-      dependencies: [
-        .targetItem(
-            name: "HashableMacroFoundation",
-            condition: .when(
-                platforms: [.macOS, .iOS, .tvOS, .watchOS, .macCatalyst]
-            )
-        ),
-        .product(name: "SwiftDiagnostics", package: "swift-syntax"),
-        .product(name: "SwiftSyntax", package: "swift-syntax"),
-        .product(name: "SwiftSyntaxMacros", package: "swift-syntax"),
-        .product(name: "SwiftCompilerPlugin", package: "swift-syntax"),
-      ],
-      swiftSettings: [.enableExperimentalFeature("StrictConcurrency")]
-    ),
-    .testTarget(
-      name: "HashableMacroTests",
-      dependencies: [
-        "HashableMacro",
-        "HashableMacroMacros",
-        .product(name: "MacroTesting", package: "swift-macro-testing"),
-        .product(name: "SwiftSyntaxMacros", package: "swift-syntax"),
-        .product(name: "SwiftSyntaxMacrosTestSupport", package: "swift-syntax"),
-      ],
-      swiftSettings: [.enableExperimentalFeature("StrictConcurrency")]
-    ),
-  ]
-)
diff --git a/Sources/HashableMacroMacros/Macros/HashableMacro+Hashable.swift b/Sources/HashableMacroMacros/Macros/HashableMacro+Hashable.swift
index fbab69e..a5d52d8 100644
--- a/Sources/HashableMacroMacros/Macros/HashableMacro+Hashable.swift
+++ b/Sources/HashableMacroMacros/Macros/HashableMacro+Hashable.swift
@@ -55,16 +55,29 @@ extension HashableMacro {
             )
         }
 
+        let hashFunctionType: AttributedTypeSyntax
+
+        #if canImport(SwiftSyntax600)
+        hashFunctionType = AttributedTypeSyntax(
+            specifiers: [
+                .simpleTypeSpecifier(SimpleTypeSpecifierSyntax(specifier: .keyword(.inout)))
+            ],
+            baseType: TypeSyntax(stringLiteral: "Hasher")
+        )
+        #else
+        hashFunctionType = AttributedTypeSyntax(
+            specifier: .keyword(.inout),
+            baseType: TypeSyntax(stringLiteral: "Hasher")
+        )
+        #endif
+
         let hashFunctionSignature = FunctionSignatureSyntax(
             parameterClause: FunctionParameterClauseSyntax(
                 parameters: [
                     FunctionParameterSyntax(
                         firstName: .identifier("into"),
                         secondName: .identifier("hasher"),
-                        type: AttributedTypeSyntax(
-                            specifier: .keyword(.inout),
-                            baseType: TypeSyntax(stringLiteral: "Hasher")
-                        )
+                        type: hashFunctionType
                     ),
                 ]
             )
diff --git a/Tests/HashableMacroTests/HashableMacroTests.swift b/Tests/HashableMacroTests/HashableMacroTests.swift
index 8c10714..77d34ef 100644
--- a/Tests/HashableMacroTests/HashableMacroTests.swift
+++ b/Tests/HashableMacroTests/HashableMacroTests.swift
@@ -192,6 +192,13 @@ final class HashableMacroTests: XCTestCase {
 
     func testEmbeddedType() throws {
         #if canImport(HashableMacroMacros)
+        #if canImport(SwiftSyntax600)
+        let outputsFullTypeName = true
+        #else
+        // This should always out e.g. `extension Outer.InnerStruct` but the tester does not output
+        // this until Swift Syntax 600.0.0.
+        let outputsFullTypeName = false
+        #endif
         assertMacro(testMacros) {
             """
             enum Outer {
@@ -212,7 +219,6 @@ final class HashableMacroTests: XCTestCase {
             }
             """
         } expansion: {
-            // This should be e.g. `extension Outer.InnerStruct` but the tester does not output this.
             """
             enum Outer {
                 struct InnerStruct {
@@ -227,25 +233,25 @@ final class HashableMacroTests: XCTestCase {
                 }
             }
 
-            extension InnerStruct {
+            extension \(outputsFullTypeName ? "Outer." : "")InnerStruct {
                 func hash(into hasher: inout Hasher) {
                     hasher.combine(self.hashedProperty)
                 }
             }
 
-            extension InnerStruct {
+            extension \(outputsFullTypeName ? "Outer." : "")InnerStruct {
                 static func ==(lhs: Self, rhs: Self) -> Bool {
                     return lhs.hashedProperty == rhs.hashedProperty
                 }
             }
 
-            extension InnerClass {
+            extension \(outputsFullTypeName ? "Outer." : "")InnerClass {
                 final func hash(into hasher: inout Hasher) {
                     hasher.combine(self.hashedProperty)
                 }
             }
 
-            extension InnerClass {
+            extension \(outputsFullTypeName ? "Outer." : "")InnerClass {
                 static func ==(lhs: Outer.InnerClass, rhs: Outer.InnerClass) -> Bool {
                     return lhs.hashedProperty == rhs.hashedProperty
                 }
@@ -1001,6 +1007,27 @@ final class HashableMacroTests: XCTestCase {
 
     func testHashedAttachedToMultiplePropertyDeclaration() throws {
         #if canImport(HashableMacroMacros)
+        #if canImport(SwiftSyntax510)
+        assertMacro(testMacros) {
+            """
+            @Hashable(_disableNSObjectSubclassSupport: true)
+            struct TestStruct {
+                @Hashed
+                var hashedProperty, secondHashedProperty: String
+            }
+            """
+        } diagnostics: {
+            """
+            @Hashable(_disableNSObjectSubclassSupport: true)
+            struct TestStruct {
+                @Hashed
+                ┬──────
+                ╰─ 🛑 peer macro can only be applied to a single variable
+                var hashedProperty, secondHashedProperty: String
+            }
+            """
+        }
+        #else
         assertMacro(testMacros) {
             """
             @Hashable(_disableNSObjectSubclassSupport: true)
@@ -1030,6 +1057,7 @@ final class HashableMacroTests: XCTestCase {
             }
             """
         }
+        #endif
         #else
         throw XCTSkip("Macros are only supported when running tests for the host platform")
         #endif
@@ -1516,8 +1544,20 @@ final class HashableMacroTests: XCTestCase {
     // MARK: - Edge cases
 
     func testPropertyAfterIfConfig() throws {
+        #if canImport(SwiftSyntax602)
+        let includesCompilerConditionals = true
+        #else
         // The `#if os(macOS)` will be parsed an attribute of the
         // `notHashedProperty` property.
+        let includesCompilerConditionals = false
+        #endif
+        let conditionalNotHashed =
+            """
+            #if os(macOS)
+                @NotHashed
+                #endif
+                
+            """
         #if canImport(HashableMacroMacros)
         assertMacro(testMacros) {
             """
@@ -1525,18 +1565,14 @@ final class HashableMacroTests: XCTestCase {
             struct Test {
                 @Hashed
                 var hashablePropery: String
-
-                #if os(macOS)
-                @NotHashed
-                #endif
-                var notHashedProperty: String
+                \(conditionalNotHashed)var notHashedProperty: String
             }
             """
         } expansion: {
             """
             struct Test {
                 var hashablePropery: String
-                var notHashedProperty: String
+                \(includesCompilerConditionals ? conditionalNotHashed : "")var notHashedProperty: String
             }
 
             extension Test {