diff --git a/.github/ISSUE_TEMPLATE/bug_report.yml b/.github/ISSUE_TEMPLATE/bug_report.yml
index 4ce9003..3d9e541 100644
--- a/.github/ISSUE_TEMPLATE/bug_report.yml
+++ b/.github/ISSUE_TEMPLATE/bug_report.yml
@@ -66,6 +66,6 @@ body:
     attributes:
       label: Environment
       description: OS and version, Xcode version.
-      placeholder: "macOS 26.1, Xcode 26.0"
+      placeholder: "macOS 27.0, Xcode 27.0"
     validations:
       required: true
diff --git a/.github/actions/select-xcode/action.yml b/.github/actions/select-xcode/action.yml
index 06d919b..54e8af4 100644
--- a/.github/actions/select-xcode/action.yml
+++ b/.github/actions/select-xcode/action.yml
@@ -7,7 +7,7 @@ description: >
 inputs:
   xcode-major:
     description: Xcode major version to select
-    default: "26"
+    default: "27"
 
 runs:
   using: composite
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d66744c..ed8f6e9 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -14,7 +14,7 @@ concurrency:
 jobs:
   build-test:
     name: Build & Test
-    runs-on: macos-15
+    runs-on: xcode-27
     permissions:
       contents: read
       id-token: write  # Codecov upload via GitHub OIDC (no static token)
@@ -34,13 +34,19 @@ jobs:
       - name: Test
         run: swift test --enable-code-coverage
 
+      # SwiftPM builds one .xctest bundle per test target (not a single
+      # <Package>PackageTests.xctest), so pass every bundle's binary to llvm-cov.
       - name: Export coverage (lcov)
         run: |
           BIN_PATH=$(swift build --show-bin-path)
+          objects=()
+          for bundle in "$BIN_PATH"/*.xctest; do
+            objects+=(-object "$bundle/Contents/MacOS/$(basename "$bundle" .xctest)")
+          done
           xcrun llvm-cov export -format=lcov \
             -instr-profile "$BIN_PATH/codecov/default.profdata" \
             -ignore-filename-regex="\.build|Tests" \
-            "$BIN_PATH/TortoiseGraphicsPackageTests.xctest/Contents/MacOS/TortoiseGraphicsPackageTests" \
+            "${objects[@]}" \
             > coverage.lcov
 
       - name: Upload coverage to Codecov
@@ -54,7 +60,7 @@ jobs:
   # parallel job, so the test job doesn't build everything twice.
   release-build:
     name: Release Build
-    runs-on: macos-15
+    runs-on: xcode-27
     steps:
       - uses: actions/checkout@v7
 
@@ -76,7 +82,7 @@ jobs:
   linux:
     name: Linux (Core + SVG)
     runs-on: ubuntu-latest
-    container: swift:6.2
+    container: swift:6.4
     steps:
       - uses: actions/checkout@v7
 
@@ -92,7 +98,7 @@ jobs:
 
   format-lint:
     name: swift-format lint
-    runs-on: macos-15
+    runs-on: xcode-27
     steps:
       - uses: actions/checkout@v7
 
diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
index e2f5789..25003b6 100644
--- a/.github/workflows/docs.yml
+++ b/.github/workflows/docs.yml
@@ -18,7 +18,7 @@ concurrency:
 jobs:
   build:
     name: Build DocC
-    runs-on: macos-15
+    runs-on: xcode-27
     steps:
       - uses: actions/checkout@v7
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index ad0c491..c8de887 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,14 @@
 # Changelog
 
+## Unreleased
+
+### Changed
+- Requires Swift 6.4+ / Xcode 27+ (was Swift 6.2+ / Xcode 26+) — the package
+  manifest now declares `swift-tools-version: 6.4`. No source changes were
+  needed: the package builds without warnings and passes all tests under
+  Swift 6.4. Platform requirements are unchanged (iOS 26+ · macOS 26+ ·
+  visionOS 26+ · Linux)
+
 ## 2.1.0
 
 ### Added
diff --git a/CLAUDE.md b/CLAUDE.md
index d023721..e04e660 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -91,7 +91,7 @@ SVG tests avoid raw string literals (`#"..."#`) when the expected string contain
 **Drawing-scenario golden tests.** `Tests/TortoiseTestSupport/` (a non-product target) defines `DrawingScenario.all` — feature-grouped tortoise programs that together cover every `TortoiseCommand` case. Both renderers are verified against the same scenarios via pointfreeco/swift-snapshot-testing:
 
 - `TortoiseSVGTests/DrawingScenarioSVGTests` compares full SVG strings against goldens in `Tests/TortoiseSVGTests/__Snapshots__/`.
-- `TortoiseUITests/DrawingScenarioCanvasTests` (macOS-only, `#if os(macOS)`) renders `TortoiseCanvas` via `ImageRenderer` (`scale = 2`, instant mode forced by prepending `speed = 0`) and compares PNGs in `Tests/TortoiseUITests/__Snapshots__/` with `precision: 0.995, perceptualPrecision: 0.98` to absorb OS-level antialiasing drift.
+- `TortoiseUITests/DrawingScenarioCanvasTests` (macOS-only, `#if os(macOS)`) renders `TortoiseCanvas` via `ImageRenderer` (`scale = 2`, instant mode forced by prepending `speed = 0`) and compares PNGs in `Tests/TortoiseUITests/__Snapshots__/` with `.canvasGolden` (byte-wise `precision: 0.995`, defined in `CanvasGoldenSnapshotting.swift`) to absorb OS-level antialiasing drift. **Do not add `perceptualPrecision`**: swift-snapshot-testing's perceptual path passes a bare `CGRect` to `CIAreaAverage`, which Core Image on macOS 27 rejects with an uncaught exception that kills the whole test process. It only triggers when bytes differ, so it passes on the recording macOS and crashes on the CI runner's. Tracked in #49 (still reproduces on Xcode 27.0 GA; re-check once the runner image ships a GA macOS 27).
 
 After intentionally changing scenario programs or renderer output, re-record **both** golden sets in the same commit and visually inspect them:
 
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index ceba104..71ff472 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -5,7 +5,7 @@ requests, documentation fixes, and pull requests are all welcome.
 
 ## Requirements
 
-- **Swift** 6.2+ / **Xcode** 26+
+- **Swift** 6.4+ / **Xcode** 27+
 - **macOS** to run the full test suite — the golden image tests in
   `TortoiseUITests` render a SwiftUI view and are macOS-only.
 
@@ -73,10 +73,14 @@ Rules:
   visible output — add or update a scenario so both renderers stay covered.
 
 The PNG goldens depend on OS-level rendering. The current set was recorded on
-**macOS 26** (Xcode 26); CI compares them on `macos-15` runners, with a small
-tolerance (`precision: 0.995`, `perceptualPrecision: 0.98`) absorbing
-antialiasing drift between OS versions. If a PR bumps the CI runner image
-(`runs-on: macos-XX`) or you re-record on a different macOS version, confirm
+**macOS 26** (Xcode 26); CI compares them on the `xcode-27` runner image
+(macOS 27), with a small
+byte-wise tolerance (`precision: 0.995`, defined once as `.canvasGolden` in
+`Tests/TortoiseUITests/CanvasGoldenSnapshotting.swift`) absorbing
+antialiasing drift between OS versions. Don't add `perceptualPrecision`: that
+comparison crashes the test process on macOS 27
+([#49](https://github.com/temoki/TortoiseGraphics2/issues/49)). If a PR bumps the CI runner image
+(`runs-on:`) or you re-record on a different macOS version, confirm
 the PNG golden tests still pass in CI — and if they don't, re-record both
 golden sets and visually inspect them as described above.
 
diff --git a/Package.swift b/Package.swift
index da5d70d..49e2fef 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,4 +1,4 @@
-// swift-tools-version: 6.2
+// swift-tools-version: 6.4
 import PackageDescription
 
 var products: [Product] = [
diff --git a/README.md b/README.md
index 5fd18af..60ad5c2 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 # TortoiseGraphics2
 
-[![Swift](https://img.shields.io/badge/Swift-6.2-orange.svg)](https://swift.org)
+[![Swift](https://img.shields.io/badge/Swift-6.4-orange.svg)](https://swift.org)
 [![Swift Package Manager](https://img.shields.io/badge/Swift%20Package%20Manager-compatible-brightgreen.svg)](https://swift.org/package-manager)
 [![License](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE)
 [![codecov](https://codecov.io/gh/temoki/TortoiseGraphics2/graph/badge.svg)](https://codecov.io/gh/temoki/TortoiseGraphics2)
@@ -68,8 +68,8 @@ and testing all share a single source of truth.
 
 ## Requirements
 
-- **Swift** 6.2+
-- **Xcode** 26+ (Apple platforms)
+- **Swift** 6.4+
+- **Xcode** 27+ (Apple platforms)
 - **Platforms** iOS 26+ · macOS 26+ · visionOS 26+ · Linux (`TortoiseCore` / `TortoiseSVG` only — `TortoiseUI` requires SwiftUI)
 
 ## Installation
diff --git a/Tests/TortoiseUITests/CanvasGoldenSnapshotting.swift b/Tests/TortoiseUITests/CanvasGoldenSnapshotting.swift
new file mode 100644
index 0000000..c88c2dc
--- /dev/null
+++ b/Tests/TortoiseUITests/CanvasGoldenSnapshotting.swift
@@ -0,0 +1,23 @@
+#if os(macOS)
+    import AppKit
+    import SnapshotTesting
+
+    extension Snapshotting where Value == NSImage, Format == NSImage {
+        /// The comparison every canvas PNG golden uses.
+        ///
+        /// Byte-wise with a small tolerance, deliberately *without*
+        /// `perceptualPrecision`. swift-snapshot-testing's perceptual path passes a
+        /// bare `CGRect` as `CIAreaAverage`'s `inputExtent`, which Core Image on
+        /// macOS 27 rejects with an uncaught `-[NSConcreteValue CGRectValue]`
+        /// exception — crashing the whole test process rather than failing one
+        /// test. An exact match never reaches that path, which is why the goldens
+        /// still pass on the macOS they were recorded on.
+        ///
+        /// Still reproduces on Xcode 27.0 GA (27A266a); the CI runner's macOS 27 is
+        /// itself still a beta build, so whether `perceptualPrecision` can ever come
+        /// back is tracked in #49.
+        static var canvasGolden: Snapshotting {
+            .image(precision: 0.995)
+        }
+    }
+#endif
diff --git a/Tests/TortoiseUITests/DrawingScenarioCanvasTests.swift b/Tests/TortoiseUITests/DrawingScenarioCanvasTests.swift
index b5aa61d..9b2a4d1 100644
--- a/Tests/TortoiseUITests/DrawingScenarioCanvasTests.swift
+++ b/Tests/TortoiseUITests/DrawingScenarioCanvasTests.swift
@@ -30,7 +30,7 @@
             }
             assertSnapshot(
                 of: image,
-                as: .image(precision: 0.995, perceptualPrecision: 0.98),
+                as: .canvasGolden,
                 named: scenario.name,
                 testName: "scenario"
             )
diff --git a/Tests/TortoiseUITests/TortoiseSpriteTests.swift b/Tests/TortoiseUITests/TortoiseSpriteTests.swift
index 964f972..ad57fc8 100644
--- a/Tests/TortoiseUITests/TortoiseSpriteTests.swift
+++ b/Tests/TortoiseUITests/TortoiseSpriteTests.swift
@@ -183,7 +183,7 @@ extension CGSize {
                 return
             }
             assertSnapshot(
-                of: image, as: .image(precision: 0.995, perceptualPrecision: 0.98),
+                of: image, as: .canvasGolden,
                 fileID: fileID, file: filePath, testName: function, line: line, column: column)
         }
     }