chemicL · Nov 9, 2026 · Nov 10, 2026
diff --git a/.github/workflows/conformance.yml b/.github/workflows/conformance.yml
@@ -107,6 +107,45 @@ jobs:
             --spec-version 2025-11-25 \
             --expected-failures ./conformance-tests/conformance-baseline.yml
 
+  modern-client:
+    name: Modern Client Conformance (2026-07-28)
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        scenario:
+        - tools_call
+        - request-metadata
+        - sep-2322-client-request-state
+        - http-standard-headers
+        - http-custom-headers
+        - http-invalid-tool-headers
+        - json-schema-ref-no-deref
+        - json-schema-2020-12-preservation
+    steps:
+      - uses: actions/checkout@v7
+
+      - name: Set up JDK 17
+        uses: actions/setup-java@v6
+        with:
+          java-version: '17'
+          distribution: 'temurin'
+          cache: 'maven'
+
+      - name: Build client
+        run: ./mvnw clean install -DskipTests
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+
+      - name: Run conformance test
+        run: |
+          npx --yes "$CONFORMANCE" client \
+            --command 'java -jar conformance-tests/client-modern/target/client-modern-*-SNAPSHOT.jar' \
+            --scenario ${{ matrix.scenario }} \
+            --spec-version 2026-07-28
+
   auth:
     name: Auth Conformance
     runs-on: ubuntu-latest

diff --git a/conformance-tests/VALIDATION_RESULTS.md b/conformance-tests/VALIDATION_RESULTS.md
@@ -9,6 +9,7 @@ Last validated: **2026-10-02** against conformance suite
 ## Summary
 
 **Modern Server Tests (2026-07-28 requirements):** 37/37 required scenarios passed (`server-servlet-modern`)
+**Modern Client Tests (2026-07-28):** 8/8 non-auth client scenarios passed, 62/62 checks (`client-modern`)
 **Server Tests (active suite):** 73/73 checks passed (31 scenarios, 100%)
 **Server Tests (SEP-1613 `json-schema-2020-12`):** 5/5 checks passed (SEP-2106 checks skipped — post-2025-11-25 spec additions)
 **Client Tests:** 3/4 scenarios passed; `sse-retry` fails (tracked in `conformance-baseline.yml`)
@@ -44,6 +45,31 @@ in the anchor release (`0.2.0-alpha.10`) as `not_scored`. Pending scenarios are
   `http-custom-header-server-validation` (10/10, SEP-2243 custom headers, against the `test_x_mcp_header` tool)
 - **Failing — tasks extension (`tasks-*`, SEP-2663):** not implemented
 
+## Modern Client Test Results (2026-07-28)
+
+The `client-modern` module drives `io.modelcontextprotocol.modern.client.McpSyncClient` over
+`HttpClientMcpTransport`. Last validated on **2026-11-05** with `--spec-version 2026-07-28`.
+
+### Passing (8/8 scenarios, 62/62 checks)
+
+- **tools_call (2/2):** tool discovery and invocation
+- **request-metadata (6/6, SEP-2575):** `_meta` with version, capabilities and client info on every
+  request, `MCP-Protocol-Version` matching `_meta`, retry after `-32022`
+- **sep-2322-client-request-state (5/5, SEP-2322):** `requestState` echoed byte for byte and omitted
+  when absent, a new JSON-RPC id per retry, no MRTR state on other requests, missing `resultType` as
+  `complete`
+- **http-standard-headers (9/9, SEP-2243):** `Mcp-Method` and `Mcp-Name` on tools, resources and prompts
+- **http-custom-headers (18/18, SEP-2243):** `Mcp-Param-*` mirroring, Base64 encoding of unsafe values,
+  omitted `null` arguments
+- **http-invalid-tool-headers (12/12, SEP-2243):** tools with invalid `x-mcp-header` annotations left out,
+  valid tools kept
+- **json-schema-ref-no-deref (1/1, SEP-2106)** and **json-schema-2020-12-preservation (9/9, SEP-1613)**
+
+### Not covered
+
+- **auth/\*:** the modern client has no OAuth support of its own; authorization plugs in through
+  `McpHttpRequestCustomizer` and `McpHttpAuthorizationErrorHandler`.
+
 ## Server Test Results
 
 ### Active Suite — Passing (31/31 scenarios, 73/73 checks)

diff --git a/conformance-tests/client-modern/README.md b/conformance-tests/client-modern/README.md
@@ -0,0 +1,41 @@
+# MCP Conformance Tests - Modern Client
+
+Conformance client for the stateless **2026-07-28** MCP revision, built on the synchronous
+`io.modelcontextprotocol.modern.client.McpSyncClient` over `HttpClientMcpTransport`. The legacy
+(2025-11-25) clients live in [`client-jdk-http-client`](../client-jdk-http-client) and
+[`client-spring-http-client`](../client-spring-http-client).
+
+Each scenario uses the client as an application would: list, call, read, get. The protocol details the
+suite checks are the client's job, so the scenarios contain none of them.
+
+## Scenarios
+
+| Scenario | What the client does |
+|---|---|
+| `tools_call` | Lists the tools and calls the first one |
+| `request-metadata` | `server/discover`, then `tools/list`; the server rejects the first request with `-32022` |
+| `sep-2322-client-request-state` | Continues one call round by round with `callOnce()`, calling another tool in between, and lets the client run the others with its elicitation handler |
+| `http-standard-headers` | Lists and uses every tool, resource and prompt |
+| `http-custom-headers` | Calls the tools named in `MCP_CONFORMANCE_CONTEXT` with their arguments |
+| `http-invalid-tool-headers` | Calls every listed tool; tools with invalid `x-mcp-header` annotations aren't listed |
+| `json-schema-ref-no-deref` | Lists the tools |
+| `json-schema-2020-12-preservation` | Sends the listed input schema back through `json_schema_echo` |
+
+The `auth/*` scenarios of the 2026-07-28 requirement set aren't covered: the modern client has no OAuth
+support of its own, only the HTTP hooks an authorization integration plugs into.
+
+## Running
+
+```bash
+./mvnw clean install -DskipTests
+
+npx @modelcontextprotocol/[email protected] client \
+  --command "java -jar conformance-tests/client-modern/target/client-modern-2.2.0-SNAPSHOT.jar" \
+  --scenario http-custom-headers \
+  --spec-version 2026-07-28
+```
+
+The client reads the scenario from `MCP_CONFORMANCE_SCENARIO`, optional scenario data from
+`MCP_CONFORMANCE_CONTEXT`, and the server URL from its last argument. It logs to stderr.
+
+See [VALIDATION_RESULTS.md](../VALIDATION_RESULTS.md) for the latest results.
diff --git a/conformance-tests/client-modern/pom.xml b/conformance-tests/client-modern/pom.xml
@@ -0,0 +1,89 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>io.modelcontextprotocol.sdk</groupId>
+		<artifactId>conformance-tests</artifactId>
+		<version>2.2.0-SNAPSHOT</version>
+	</parent>
+	<artifactId>client-modern</artifactId>
+	<packaging>jar</packaging>
+	<name>MCP Conformance Tests - Modern Client</name>
+	<description>Conformance client for the modern (2026-07-28) Java MCP SDK client</description>
+	<url>https://github.com/modelcontextprotocol/java-sdk</url>
+
+	<scm>
+		<url>https://github.com/modelcontextprotocol/java-sdk</url>
+		<connection>scm:git:git://github.com/modelcontextprotocol/java-sdk.git</connection>
+		<developerConnection>scm:git:ssh://[email protected]/modelcontextprotocol/java-sdk.git</developerConnection>
+	</scm>
+
+	<properties>
+		<module.name>io.modelcontextprotocol.sdk.conformance.client.modern</module.name>
+		<maven.deploy.skip>true</maven.deploy.skip>
+	</properties>
+
+	<dependencies>
+		<dependency>
+			<groupId>io.modelcontextprotocol.sdk</groupId>
+			<artifactId>mcp-core</artifactId>
+			<version>2.2.0-SNAPSHOT</version>
+		</dependency>
+		<dependency>
+			<groupId>io.modelcontextprotocol.sdk</groupId>
+			<artifactId>mcp-json-jackson3</artifactId>
+			<version>2.2.0-SNAPSHOT</version>
+		</dependency>
+
+		<!-- Logging -->
+		<dependency>
+			<groupId>ch.qos.logback</groupId>
+			<artifactId>logback-classic</artifactId>
+			<version>${logback.version}</version>
+			<scope>runtime</scope>
+		</dependency>
+	</dependencies>
+
+	<build>
+		<plugins>
+			<!-- Maven Shade Plugin for creating executable JAR with dependencies -->
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-shade-plugin</artifactId>
+				<version>3.6.2</version>
+				<executions>
+					<execution>
+						<phase>package</phase>
+						<goals>
+							<goal>shade</goal>
+						</goals>
+						<configuration>
+							<transformers>
+								<transformer
+									implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
+									<mainClass>
+										io.modelcontextprotocol.conformance.client.modern.ModernConformanceClient</mainClass>
+								</transformer>
+								<transformer
+									implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer" />
+							</transformers>
+							<filters>
+								<filter>
+									<artifact>*:*</artifact>
+									<excludes>
+										<exclude>META-INF/*.SF</exclude>
+										<exclude>META-INF/*.DSA</exclude>
+										<exclude>META-INF/*.RSA</exclude>
+									</excludes>
+								</filter>
+							</filters>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
+		</plugins>
+	</build>
+
+</project>