diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d8f1ecae..224c468e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -118,6 +118,41 @@ jobs:
           path: examples/target/generated-pdfs/**
           if-no-files-found: error
 
+  binary-compat:
+    name: Binary Compatibility (japicmp vs v1.6.5)
+    if: github.event_name == 'pull_request'
+    needs: architecture-and-documentation-guards
+    runs-on: ubuntu-latest
+    env:
+      JAVA_TOOL_OPTIONS: -Djava.awt.headless=true
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v6
+
+      - name: Set up Temurin JDK 17
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: '17'
+          cache: maven
+
+      - name: Compare public API against baseline
+        # The `japicmp` profile pulls the v1.6.5 jar from JitPack and
+        # diffs it against the freshly-built artifact. Fails the job on
+        # any binary-incompatible modification to the public surface.
+        # Source-incompatible changes are reported only (phased policy).
+        # See Track E1 in the v1.6.5→1.7 readiness taskboard.
+        run: ./mvnw -B -ntp -DskipTests -P japicmp verify -pl .
+
+      - name: Upload japicmp report
+        if: always()
+        uses: actions/upload-artifact@v7
+        with:
+          name: japicmp-report-${{ github.run_id }}
+          path: target/japicmp/**
+          if-no-files-found: ignore
+
   perf-smoke:
     name: Performance Smoke Check
     if: github.event_name == 'pull_request'
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c7c30d53..484b3c5a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,25 @@
 All notable changes to GraphCompose are documented here. Versions
 follow semantic versioning; release dates are ISO 8601.
 
+## v1.6.6 — Planned
+
+First Maven Central release. Adds publishable sources/javadoc jars,
+GPG-signed artifacts, a binary-compatibility gate against v1.6.5, and
+the metadata Maven Central requires. Zero breaking changes; users on
+JitPack continue to resolve through the existing coordinates.
+
+### Build
+
+- **Binary-compatibility gate against v1.6.5** (`japicmp` profile,
+  Track E1). The new `binary-compat` CI job builds the artifact on every
+  pull request and diffs it against `com.github.DemchaAV:GraphCompose:v1.6.5`
+  pulled from JitPack. Binary-incompatible modifications to the public
+  surface fail the build; source-incompatible changes are reported only
+  (phased policy, will tighten after the 1.6.6 cut). Run locally with
+  `./mvnw -DskipTests -P japicmp verify -pl .`; HTML/MD/XML reports
+  land in `target/japicmp/`. JitPack repository is scoped to the
+  `japicmp` profile, so downstream consumers do not inherit it.
+
 ## v1.6.5 — 2026-05-30
 
 ### Templates v2
diff --git a/pom.xml b/pom.xml
index cc3dc92b..7242a31c 100644
--- a/pom.xml
+++ b/pom.xml
@@ -68,6 +68,10 @@
         <maven.compiler.plugin.version>3.15.0</maven.compiler.plugin.version>
         <maven.javadoc.plugin.version>3.12.0</maven.javadoc.plugin.version>
         <maven.surefire.plugin.version>3.5.5</maven.surefire.plugin.version>
+
+        <!-- Binary compatibility baseline (japicmp profile) -->
+        <japicmp.version>0.23.1</japicmp.version>
+        <japicmp.baseline>v1.6.5</japicmp.baseline>
     </properties>
 
     <dependencyManagement>
@@ -355,4 +359,66 @@
             </plugin>
         </plugins>
     </build>
+
+    <profiles>
+        <!--
+            Binary-compatibility baseline against the last published
+            release. Activated with `-P japicmp`. Resolves the baseline
+            artifact from JitPack (kept profile-local so consumers do
+            NOT inherit a JitPack repository). Fails the build on any
+            binary-incompatible modification to the public surface;
+            source-incompatible changes are reported but do not fail
+            (yet) so the team can phase the policy in. Tracked in the
+            v1.6.6 stabilization (Track E1).
+        -->
+        <profile>
+            <id>japicmp</id>
+            <repositories>
+                <repository>
+                    <id>jitpack.io</id>
+                    <url>https://jitpack.io</url>
+                </repository>
+            </repositories>
+            <build>
+                <plugins>
+                    <plugin>
+                        <groupId>com.github.siom79.japicmp</groupId>
+                        <artifactId>japicmp-maven-plugin</artifactId>
+                        <version>${japicmp.version}</version>
+                        <executions>
+                            <execution>
+                                <id>japicmp-against-baseline</id>
+                                <phase>verify</phase>
+                                <goals>
+                                    <goal>cmp</goal>
+                                </goals>
+                            </execution>
+                        </executions>
+                        <configuration>
+                            <oldVersion>
+                                <dependency>
+                                    <groupId>com.github.DemchaAV</groupId>
+                                    <artifactId>GraphCompose</artifactId>
+                                    <version>${japicmp.baseline}</version>
+                                </dependency>
+                            </oldVersion>
+                            <newVersion>
+                                <file>
+                                    <path>${project.build.directory}/${project.build.finalName}.jar</path>
+                                </file>
+                            </newVersion>
+                            <parameter>
+                                <onlyModified>true</onlyModified>
+                                <breakBuildOnBinaryIncompatibleModifications>true</breakBuildOnBinaryIncompatibleModifications>
+                                <breakBuildOnSourceIncompatibleModifications>false</breakBuildOnSourceIncompatibleModifications>
+                                <includeSynthetic>false</includeSynthetic>
+                                <reportOnlyFilename>true</reportOnlyFilename>
+                                <skipPomModules>true</skipPomModules>
+                            </parameter>
+                        </configuration>
+                    </plugin>
+                </plugins>
+            </build>
+        </profile>
+    </profiles>
 </project>