diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 974ab4e..b11ca71 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -13,6 +13,19 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
+      # Zig 0.15.1 cannot read the arm64e-only stubs in macOS SDK 26.4+.
+      # Keep the ARM runner and Zig version; select a compatible installed SDK.
+      - name: Select compatible macOS SDK
+        if: runner.os == 'macOS'
+        env:
+          DEVELOPER_DIR: /Applications/Xcode_26.2.app/Contents/Developer
+        run: |
+          test -d "$DEVELOPER_DIR"
+          echo "DEVELOPER_DIR=$DEVELOPER_DIR" >> "$GITHUB_ENV"
+          sdkroot="$(xcrun --sdk macosx --show-sdk-path)"
+          echo "SDKROOT=$sdkroot" >> "$GITHUB_ENV"
+          xcodebuild -version
+          xcrun --sdk macosx --show-sdk-version
       - uses: mlugg/setup-zig@v2
         with:
           version: 0.15.1
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 951f3d7..98db2db 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,9 +1,15 @@
 # Changelog
 
-## Unreleased
+## 0.4.0
 
-- Frontend-inline option length decoding to avoid error-result stack temporaries
-- Exhaustively check option length values, truncation/overflow errors and cursor movement
+- Add public `Observe` values for subscribe/unsubscribe requests (#7)
+- Frontend-inline option length decoding to avoid error-result stack temporaries (#8)
+- Exhaustively check option length values, truncation/overflow errors and cursor movement (#8)
+
+## 0.3.0
+
+- Add allocation-free `Packet.peekKind`, `Packet.peekMsgId`, and `Packet.peekOption` helpers (#6)
+- Add `Packet.emptyAck` and `Packet.emptyRst` wire helpers (#6)
 
 ## 0.2.1
 
diff --git a/README.md b/README.md
index 9c96dea..c29646a 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,13 @@ Handles binary CoAP message serialization only -- no transport, no retransmissio
 - RFC 7959 -- Block-Wise Transfers (option parsing)
 - RFC 8516 -- Too Many Requests Response Code
 
+## Toolchain
+
+The minimum Zig version is 0.15.1. On Apple Silicon, unpatched Zig 0.15 cannot
+read the arm64e-only system-library stubs in macOS SDK 26.4 and newer. Select a
+compatible Xcode installation using `DEVELOPER_DIR`; CI uses Xcode 26.2/SDK 26.2
+without changing the Zig version or ARM runner.
+
 ## Installation
 
 Add as a Zig package dependency:
diff --git a/build.zig.zon b/build.zig.zon
index 52555d7..3fb096f 100644
--- a/build.zig.zon
+++ b/build.zig.zon
@@ -1,6 +1,6 @@
 .{
     .name = .coapz,
-    .version = "0.3.0",
+    .version = "0.4.0",
     .minimum_zig_version = "0.15.1",
     .fingerprint = 0xad0f5d16c82d3290,
     .dependencies = .{},