feat: implement MCP protocol version per transport support (#404)

- Add protocolVersion() method to transport and transport provider interfaces and implementations
- Replace hardcoded HTTP header strings with HttpHeaders constants
- Update protocol versions to be transport-specific rather than global
- Deprecate McpSchema.LATEST_PROTOCOL_VERSION in favor of transport-specific versions
- Standardize header names: MCP-Protocol-Version, mcp-session-id, last-event-id
- Update clients and servers to use transport.protocolVersion() for initialization
- Refactor tests to use transport-specific protocol versions
- Include MCP-Protocol-Version header in all GET/POST/DELETE requests
- Update WebClientStreamableHttpTransport, WebFluxSseClientTransport,
  HttpClientSseClientTransport, and HttpClientStreamableHttpTransport

Related to #398 , #363 , #250

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/client/transport/WebClientStreamableHttpTransport.java

@@ -23,6 +23,7 @@ import com.fasterxml.jackson.databind.ObjectMapper;
 
 import io.modelcontextprotocol.spec.DefaultMcpTransportSession;
 import io.modelcontextprotocol.spec.DefaultMcpTransportStream;
+import io.modelcontextprotocol.spec.HttpHeaders;
 import io.modelcontextprotocol.spec.McpClientTransport;
 import io.modelcontextprotocol.spec.McpError;
 import io.modelcontextprotocol.spec.McpSchema;
@@ -66,6 +67,8 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
 
 	private static final Logger logger = LoggerFactory.getLogger(WebClientStreamableHttpTransport.class);
 
+	private static final String MCP_PROTOCOL_VERSION = "2025-03-26";
+
 	private static final String DEFAULT_ENDPOINT = "/mcp";
 
 	/**
@@ -103,6 +106,11 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
 		this.activeSession.set(createTransportSession());
 	}
 
+	@Override
+	public String protocolVersion() {
+		return MCP_PROTOCOL_VERSION;
+	}
+
 	/**
 	 * Create a stateful builder for creating {@link WebClientStreamableHttpTransport}
 	 * instances.
@@ -128,12 +136,20 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
 
 	private DefaultMcpTransportSession createTransportSession() {
 		Function<String, Publisher<Void>> onClose = sessionId -> sessionId == null ? Mono.empty()
-				: webClient.delete().uri(this.endpoint).headers(httpHeaders -> {
+				: webClient.delete()
-					httpHeaders.add("mcp-session-id", sessionId);
+					.uri(this.endpoint)
-				}).retrieve().toBodilessEntity().onErrorComplete(e -> {
+					.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
-					logger.warn("Got error when closing transport", e);
+					.headers(httpHeaders -> {
-					return true;
+						httpHeaders.add(HttpHeaders.MCP_SESSION_ID, sessionId);
-				}).then();
+						httpHeaders.add(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION);
+					})
+					.retrieve()
+					.toBodilessEntity()
+					.onErrorComplete(e -> {
+						logger.warn("Got error when closing transport", e);
+						return true;
+					})
+					.then();
 		return new DefaultMcpTransportSession(onClose);
 	}
 
@@ -186,10 +202,11 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
 			Disposable connection = webClient.get()
 				.uri(this.endpoint)
 				.accept(MediaType.TEXT_EVENT_STREAM)
+				.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
 				.headers(httpHeaders -> {
-					transportSession.sessionId().ifPresent(id -> httpHeaders.add("mcp-session-id", id));
+					transportSession.sessionId().ifPresent(id -> httpHeaders.add(HttpHeaders.MCP_SESSION_ID, id));
 					if (stream != null) {
-						stream.lastId().ifPresent(id -> httpHeaders.add("last-event-id", id));
+						stream.lastId().ifPresent(id -> httpHeaders.add(HttpHeaders.LAST_EVENT_ID, id));
 					}
 				})
 				.exchangeToFlux(response -> {
@@ -246,13 +263,14 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
 			Disposable connection = webClient.post()
 				.uri(this.endpoint)
 				.accept(MediaType.APPLICATION_JSON, MediaType.TEXT_EVENT_STREAM)
+				.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
 				.headers(httpHeaders -> {
-					transportSession.sessionId().ifPresent(id -> httpHeaders.add("mcp-session-id", id));
+					transportSession.sessionId().ifPresent(id -> httpHeaders.add(HttpHeaders.MCP_SESSION_ID, id));
 				})
 				.bodyValue(message)
 				.exchangeToFlux(response -> {
 					if (transportSession
-						.markInitialized(response.headers().asHttpHeaders().getFirst("mcp-session-id"))) {
+						.markInitialized(response.headers().asHttpHeaders().getFirst(HttpHeaders.MCP_SESSION_ID))) {
 						// Once we have a session, we try to open an async stream for
 						// the server to send notifications and requests out-of-band.
 						reconnect(null).contextWrite(sink.contextView()).subscribe();

mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/client/transport/WebFluxSseClientTransport.java

@@ -9,6 +9,8 @@ import java.util.function.Function;
 
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
+
+import io.modelcontextprotocol.spec.HttpHeaders;
 import io.modelcontextprotocol.spec.McpClientTransport;
 import io.modelcontextprotocol.spec.McpError;
 import io.modelcontextprotocol.spec.McpSchema;
@@ -62,6 +64,8 @@ public class WebFluxSseClientTransport implements McpClientTransport {
 
 	private static final Logger logger = LoggerFactory.getLogger(WebFluxSseClientTransport.class);
 
+	private static final String MCP_PROTOCOL_VERSION = "2024-11-05";
+
 	/**
 	 * Event type for JSON-RPC messages received through the SSE connection. The server
 	 * sends messages with this event type to transmit JSON-RPC protocol data.
@@ -166,6 +170,11 @@ public class WebFluxSseClientTransport implements McpClientTransport {
 		this.sseEndpoint = sseEndpoint;
 	}
 
+	@Override
+	public String protocolVersion() {
+		return MCP_PROTOCOL_VERSION;
+	}
+
 	/**
 	 * Establishes a connection to the MCP server using Server-Sent Events (SSE). This
 	 * method initiates the SSE connection and sets up the message processing pipeline.
@@ -250,6 +259,7 @@ public class WebFluxSseClientTransport implements McpClientTransport {
 				return webClient.post()
 					.uri(messageEndpointUri)
 					.contentType(MediaType.APPLICATION_JSON)
+					.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
 					.bodyValue(jsonText)
 					.retrieve()
 					.toBodilessEntity()
@@ -282,6 +292,7 @@ public class WebFluxSseClientTransport implements McpClientTransport {
 			.get()
 			.uri(this.sseEndpoint)
 			.accept(MediaType.TEXT_EVENT_STREAM)
+			.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
 			.retrieve()
 			.bodyToFlux(SSE_TYPE)
 			.retryWhen(Retry.from(retrySignal -> retrySignal.handle(inboundRetryHandler)));

mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/server/transport/WebFluxSseServerTransportProvider.java

@@ -79,6 +79,8 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 	 */
 	public static final String ENDPOINT_EVENT_TYPE = "endpoint";
 
+	private static final String MCP_PROTOCOL_VERSION = "2025-06-18";
+
 	/**
 	 * Default SSE endpoint path as specified by the MCP transport specification.
 	 */
@@ -212,6 +214,11 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 		}
 	}
 
+	@Override
+	public String protocolVersion() {
+		return "2024-11-05";
+	}
+
 	@Override
 	public void setSessionFactory(McpServerSession.Factory sessionFactory) {
 		this.sessionFactory = sessionFactory;

mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/server/transport/WebFluxStatelessServerTransport.java

@@ -21,7 +21,6 @@ import reactor.core.publisher.Mono;
 
 import java.io.IOException;
 import java.util.List;
-import java.util.function.Function;
 
 /**
  * Implementation of a WebFlux based {@link McpStatelessServerTransport}.

mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/server/transport/WebFluxStreamableServerTransportProvider.java

@@ -95,6 +95,11 @@ public class WebFluxStreamableServerTransportProvider implements McpStreamableSe
 
 	}
 
+	@Override
+	public String protocolVersion() {
+		return "2025-03-26";
+	}
+
 	@Override
 	public void setSessionFactory(McpStreamableServerSession.Factory sessionFactory) {
 		this.sessionFactory = sessionFactory;

mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcSseServerTransportProvider.java

@@ -209,6 +209,11 @@ public class WebMvcSseServerTransportProvider implements McpServerTransportProvi
 		}
 	}
 
+	@Override
+	public String protocolVersion() {
+		return "2024-11-05";
+	}
+
 	@Override
 	public void setSessionFactory(McpServerSession.Factory sessionFactory) {
 		this.sessionFactory = sessionFactory;

mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcStreamableServerTransportProvider.java

@@ -147,6 +147,11 @@ public class WebMvcStreamableServerTransportProvider implements McpStreamableSer
 		}
 	}
 
+	@Override
+	public String protocolVersion() {
+		return "2025-03-26";
+	}
+
 	@Override
 	public void setSessionFactory(McpStreamableServerSession.Factory sessionFactory) {
 		this.sessionFactory = sessionFactory;

mcp-spring/mcp-spring-webmvc/src/test/java/io/modelcontextprotocol/server/WebMvcSseCustomContextPathTests.java

@@ -91,8 +91,15 @@ class WebMvcSseCustomContextPathTests {
 		@Bean
 		public WebMvcSseServerTransportProvider webMvcSseServerTransportProvider() {
 
-			return new WebMvcSseServerTransportProvider(new ObjectMapper(), CUSTOM_CONTEXT_PATH, MESSAGE_ENDPOINT,
+			return WebMvcSseServerTransportProvider.builder()
-					WebMvcSseServerTransportProvider.DEFAULT_SSE_ENDPOINT);
+				.objectMapper(new ObjectMapper())
+				.baseUrl(CUSTOM_CONTEXT_PATH)
+				.messageEndpoint(MESSAGE_ENDPOINT)
+				.sseEndpoint(WebMvcSseServerTransportProvider.DEFAULT_SSE_ENDPOINT)
+				.build();
+			// return new WebMvcSseServerTransportProvider(new ObjectMapper(),
+			// CUSTOM_CONTEXT_PATH, MESSAGE_ENDPOINT,
+			// WebMvcSseServerTransportProvider.DEFAULT_SSE_ENDPOINT);
 		}
 
 		@Bean

mcp/src/main/java/io/modelcontextprotocol/client/McpAsyncClient.java

@@ -272,9 +272,8 @@ public class McpAsyncClient {
 				asyncProgressNotificationHandler(progressConsumersFinal));
 
 		this.initializer = new LifecycleInitializer(clientCapabilities, clientInfo,
-				List.of(McpSchema.LATEST_PROTOCOL_VERSION), initializationTimeout,
+				List.of(transport.protocolVersion()), initializationTimeout, ctx -> new McpClientSession(requestTimeout,
-				ctx -> new McpClientSession(requestTimeout, transport, requestHandlers, notificationHandlers,
+						transport, requestHandlers, notificationHandlers, con -> con.contextWrite(ctx)));
-						con -> con.contextWrite(ctx)));
 		this.transport.setExceptionHandler(this.initializer::handleException);
 	}
 

mcp/src/main/java/io/modelcontextprotocol/client/transport/HttpClientSseClientTransport.java

@@ -61,6 +61,10 @@ import reactor.core.publisher.Sinks;
  */
 public class HttpClientSseClientTransport implements McpClientTransport {
 
+	private static final String MCP_PROTOCOL_VERSION = "2024-11-05";
+
+	private static final String MCP_PROTOCOL_VERSION_HEADER_NAME = "MCP-Protocol-Version";
+
 	private static final Logger logger = LoggerFactory.getLogger(HttpClientSseClientTransport.class);
 
 	/** SSE event type for JSON-RPC messages */
@@ -211,6 +215,11 @@ public class HttpClientSseClientTransport implements McpClientTransport {
 		this.httpRequestCustomizer = httpRequestCustomizer;
 	}
 
+	@Override
+	public String protocolVersion() {
+		return MCP_PROTOCOL_VERSION;
+	}
+
 	/**
 	 * Creates a new builder for {@link HttpClientSseClientTransport}.
 	 * @param baseUri the base URI of the MCP server
@@ -391,6 +400,7 @@ public class HttpClientSseClientTransport implements McpClientTransport {
 				.uri(uri)
 				.header("Accept", "text/event-stream")
 				.header("Cache-Control", "no-cache")
+				.header(MCP_PROTOCOL_VERSION_HEADER_NAME, MCP_PROTOCOL_VERSION)
 				.GET();
 			return Mono.from(this.httpRequestCustomizer.customize(builder, "GET", uri, null));
 		}).flatMap(requestBuilder -> Mono.create(sink -> {
@@ -516,7 +526,10 @@ public class HttpClientSseClientTransport implements McpClientTransport {
 	private Mono<HttpResponse<String>> sendHttpPost(final String endpoint, final String body) {
 		final URI requestUri = Utils.resolveUri(baseUri, endpoint);
 		return Mono.defer(() -> {
-			var builder = this.requestBuilder.copy().uri(requestUri).POST(HttpRequest.BodyPublishers.ofString(body));
+			var builder = this.requestBuilder.copy()
+				.uri(requestUri)
+				.header(MCP_PROTOCOL_VERSION_HEADER_NAME, MCP_PROTOCOL_VERSION)
+				.POST(HttpRequest.BodyPublishers.ofString(body));
 			return Mono.from(this.httpRequestCustomizer.customize(builder, "POST", requestUri, body));
 		}).flatMap(customizedBuilder -> {
 			var request = customizedBuilder.build();

mcp/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java

@@ -28,6 +28,7 @@ import com.fasterxml.jackson.databind.ObjectMapper;
 import io.modelcontextprotocol.client.transport.ResponseSubscribers.ResponseEvent;
 import io.modelcontextprotocol.spec.DefaultMcpTransportSession;
 import io.modelcontextprotocol.spec.DefaultMcpTransportStream;
+import io.modelcontextprotocol.spec.HttpHeaders;
 import io.modelcontextprotocol.spec.McpClientTransport;
 import io.modelcontextprotocol.spec.McpError;
 import io.modelcontextprotocol.spec.McpSchema;
@@ -72,6 +73,8 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
 
 	private static final Logger logger = LoggerFactory.getLogger(HttpClientStreamableHttpTransport.class);
 
+	private static final String MCP_PROTOCOL_VERSION = "2025-03-26";
+
 	private static final String DEFAULT_ENDPOINT = "/mcp";
 
 	/**
@@ -131,6 +134,11 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
 		this.httpRequestCustomizer = httpRequestCustomizer;
 	}
 
+	@Override
+	public String protocolVersion() {
+		return MCP_PROTOCOL_VERSION;
+	}
+
 	public static Builder builder(String baseUri) {
 		return new Builder(baseUri);
 	}
@@ -157,12 +165,14 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
 	}
 
 	private Publisher<Void> createDelete(String sessionId) {
+
 		var uri = Utils.resolveUri(this.baseUri, this.endpoint);
 		return Mono.defer(() -> {
 			var builder = this.requestBuilder.copy()
 				.uri(uri)
 				.header("Cache-Control", "no-cache")
-				.header("mcp-session-id", sessionId)
+				.header(HttpHeaders.MCP_SESSION_ID, sessionId)
+				.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
 				.DELETE();
 			return Mono.from(this.httpRequestCustomizer.customize(builder, "DELETE", uri, null));
 		}).flatMap(requestBuilder -> {
@@ -221,16 +231,18 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
 				HttpRequest.Builder requestBuilder = this.requestBuilder.copy();
 
 				if (transportSession != null && transportSession.sessionId().isPresent()) {
-					requestBuilder = requestBuilder.header("mcp-session-id", transportSession.sessionId().get());
+					requestBuilder = requestBuilder.header(HttpHeaders.MCP_SESSION_ID,
+							transportSession.sessionId().get());
 				}
 
 				if (stream != null && stream.lastId().isPresent()) {
-					requestBuilder = requestBuilder.header("last-event-id", stream.lastId().get());
+					requestBuilder = requestBuilder.header(HttpHeaders.LAST_EVENT_ID, stream.lastId().get());
 				}
 
 				var builder = requestBuilder.uri(uri)
 					.header("Accept", TEXT_EVENT_STREAM)
 					.header("Cache-Control", "no-cache")
+					.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
 					.GET();
 				return Mono.from(this.httpRequestCustomizer.customize(builder, "GET", uri, null));
 			})
@@ -377,13 +389,15 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
 				HttpRequest.Builder requestBuilder = this.requestBuilder.copy();
 
 				if (transportSession != null && transportSession.sessionId().isPresent()) {
-					requestBuilder = requestBuilder.header("mcp-session-id", transportSession.sessionId().get());
+					requestBuilder = requestBuilder.header(HttpHeaders.MCP_SESSION_ID,
+							transportSession.sessionId().get());
 				}
 
 				var builder = requestBuilder.uri(uri)
 					.header("Accept", APPLICATION_JSON + ", " + TEXT_EVENT_STREAM)
 					.header("Content-Type", APPLICATION_JSON)
 					.header("Cache-Control", "no-cache")
+					.header(HttpHeaders.PROTOCOL_VERSION, MCP_PROTOCOL_VERSION)
 					.POST(HttpRequest.BodyPublishers.ofString(jsonBody));
 				return Mono.from(this.httpRequestCustomizer.customize(builder, "GET", uri, jsonBody));
 			}).flatMapMany(requestBuilder -> Flux.<ResponseEvent>create(responseEventSink -> {

mcp/src/main/java/io/modelcontextprotocol/server/McpAsyncServer.java

@@ -115,7 +115,7 @@ public class McpAsyncServer {
 
 	private final ConcurrentHashMap<McpSchema.CompleteReference, McpServerFeatures.AsyncCompletionSpecification> completions = new ConcurrentHashMap<>();
 
-	private List<String> protocolVersions = List.of(McpSchema.LATEST_PROTOCOL_VERSION);
+	private List<String> protocolVersions;
 
 	private McpUriTemplateManagerFactory uriTemplateManagerFactory = new DeafaultMcpUriTemplateManagerFactory();
 
@@ -145,6 +145,8 @@ public class McpAsyncServer {
 		Map<String, McpRequestHandler<?>> requestHandlers = prepareRequestHandlers();
 		Map<String, McpNotificationHandler> notificationHandlers = prepareNotificationHandlers(features);
 
+		this.protocolVersions = List.of(mcpTransportProvider.protocolVersion());
+
 		mcpTransportProvider.setSessionFactory(transport -> new McpServerSession(UUID.randomUUID().toString(),
 				requestTimeout, transport, this::asyncInitializeRequestHandler, requestHandlers, notificationHandlers));
 	}
@@ -168,6 +170,8 @@ public class McpAsyncServer {
 		Map<String, McpRequestHandler<?>> requestHandlers = prepareRequestHandlers();
 		Map<String, McpNotificationHandler> notificationHandlers = prepareNotificationHandlers(features);
 
+		this.protocolVersions = List.of(mcpTransportProvider.protocolVersion());
+
 		mcpTransportProvider.setSessionFactory(new DefaultMcpStreamableServerSessionFactory(requestTimeout,
 				this::asyncInitializeRequestHandler, requestHandlers, notificationHandlers));
 	}

mcp/src/main/java/io/modelcontextprotocol/server/McpStatelessAsyncServer.java

@@ -63,7 +63,7 @@ public class McpStatelessAsyncServer {
 
 	private final ConcurrentHashMap<McpSchema.CompleteReference, McpStatelessServerFeatures.AsyncCompletionSpecification> completions = new ConcurrentHashMap<>();
 
-	private List<String> protocolVersions = List.of(McpSchema.LATEST_PROTOCOL_VERSION);
+	private List<String> protocolVersions;
 
 	private McpUriTemplateManagerFactory uriTemplateManagerFactory = new DeafaultMcpUriTemplateManagerFactory();
 
@@ -118,6 +118,8 @@ public class McpStatelessAsyncServer {
 			requestHandlers.put(McpSchema.METHOD_COMPLETION_COMPLETE, completionCompleteRequestHandler());
 		}
 
+		this.protocolVersions = List.of(mcpTransport.protocolVersion());
+
 		McpStatelessServerHandler handler = new DefaultMcpStatelessServerHandler(requestHandlers, Map.of());
 		mcpTransport.setMcpHandler(handler);
 	}

mcp/src/main/java/io/modelcontextprotocol/server/transport/HttpServletSseServerTransportProvider.java

@@ -178,6 +178,11 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
 		}
 	}
 
+	@Override
+	public String protocolVersion() {
+		return "2024-11-05";
+	}
+
 	/**
 	 * Creates a new HttpServletSseServerTransportProvider instance with the default SSE
 	 * endpoint.

mcp/src/main/java/io/modelcontextprotocol/server/transport/HttpServletStreamableServerTransportProvider.java

@@ -154,6 +154,11 @@ public class HttpServletStreamableServerTransportProvider extends HttpServlet
 
 	}
 
+	@Override
+	public String protocolVersion() {
+		return "2025-03-26";
+	}
+
 	@Override
 	public void setSessionFactory(McpStreamableServerSession.Factory sessionFactory) {
 		this.sessionFactory = sessionFactory;

mcp/src/main/java/io/modelcontextprotocol/server/transport/StdioServerTransportProvider.java

@@ -88,6 +88,11 @@ public class StdioServerTransportProvider implements McpServerTransportProvider
 		this.outputStream = outputStream;
 	}
 
+	@Override
+	public String protocolVersion() {
+		return "2024-11-05";
+	}
+
 	@Override
 	public void setSessionFactory(McpServerSession.Factory sessionFactory) {
 		// Create a single session for the stdio connection

mcp/src/main/java/io/modelcontextprotocol/spec/HttpHeaders.java

@@ -17,4 +17,9 @@ public interface HttpHeaders {
 	 */
 	String LAST_EVENT_ID = "last-event-id";
 
+	/**
+	 * Identifies the MCP protocol version.
+	 */
+	String PROTOCOL_VERSION = "MCP-Protocol-Version";
+
 }

mcp/src/main/java/io/modelcontextprotocol/spec/McpSchema.java

@@ -44,6 +44,7 @@ public final class McpSchema {
 	private McpSchema() {
 	}
 
+	@Deprecated
 	public static final String LATEST_PROTOCOL_VERSION = "2025-03-26";
 
 	public static final String JSONRPC_VERSION = "2.0";

mcp/src/main/java/io/modelcontextprotocol/spec/McpServerTransportProviderBase.java

@@ -55,4 +55,12 @@ public interface McpServerTransportProviderBase {
 	 */
 	Mono<Void> closeGracefully();
 
+	/**
+	 * Returns the protocol version supported by this transport provider.
+	 * @return the protocol version as a string
+	 */
+	default String protocolVersion() {
+		return "2024-11-05";
+	}
+
 }

mcp/src/main/java/io/modelcontextprotocol/spec/McpStatelessServerTransport.java

@@ -22,4 +22,8 @@ public interface McpStatelessServerTransport {
 	 */
 	Mono<Void> closeGracefully();
 
+	default String protocolVersion() {
+		return "2025-03-26";
+	}
+
 }