diff --git a/mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcStreamableServerTransportProvider.java b/mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcStreamableServerTransportProvider.java
index fa51a013..df5babae 100644
--- a/mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcStreamableServerTransportProvider.java
+++ b/mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcStreamableServerTransportProvider.java
@@ -90,7 +90,7 @@ public class WebMvcStreamableServerTransportProvider implements McpStreamableSer
 	private McpStreamableServerSession.Factory sessionFactory;
 
 	/**
-	 * Map of active client sessions, keyed by mcp-session-id.
+	 * Map of active client sessions, keyed by Mcp-Session-Id.
 	 */
 	private final ConcurrentHashMap<String, McpStreamableServerSession> sessions = new ConcurrentHashMap<>();
 
@@ -241,7 +241,7 @@ private ServerResponse handleGet(ServerRequest request) {
 		McpTransportContext transportContext = this.contextExtractor.extract(request, new DefaultMcpTransportContext());
 
 		if (!request.headers().asHttpHeaders().containsKey(HttpHeaders.MCP_SESSION_ID)) {
-			return ServerResponse.badRequest().body("Session ID required in mcp-session-id header");
+			return ServerResponse.badRequest().body("Session ID required in " + HttpHeaders.MCP_SESSION_ID + " header");
 		}
 
 		String sessionId = request.headers().asHttpHeaders().getFirst(HttpHeaders.MCP_SESSION_ID);
@@ -434,7 +434,7 @@ private ServerResponse handleDelete(ServerRequest request) {
 		McpTransportContext transportContext = this.contextExtractor.extract(request, new DefaultMcpTransportContext());
 
 		if (!request.headers().asHttpHeaders().containsKey(HttpHeaders.MCP_SESSION_ID)) {
-			return ServerResponse.badRequest().body("Session ID required in mcp-session-id header");
+			return ServerResponse.badRequest().body("Session ID required in " + HttpHeaders.MCP_SESSION_ID + " header");
 		}
 
 		String sessionId = request.headers().asHttpHeaders().getFirst(HttpHeaders.MCP_SESSION_ID);
diff --git a/mcp/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java b/mcp/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java
index 3cfa7359..f61ba139 100644
--- a/mcp/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java
+++ b/mcp/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java
@@ -416,8 +416,10 @@ public Mono<Void> sendMessage(McpSchema.JSONRPCMessage sentMessage) {
 					})).onErrorMap(CompletionException.class, t -> t.getCause()).onErrorComplete().subscribe();
 
 			})).flatMap(responseEvent -> {
-				if (transportSession.markInitialized(
-						responseEvent.responseInfo().headers().firstValue("mcp-session-id").orElseGet(() -> null))) {
+				if (transportSession.markInitialized(responseEvent.responseInfo()
+					.headers()
+					.firstValue(HttpHeaders.MCP_SESSION_ID)
+					.orElseGet(() -> null))) {
 					// Once we have a session, we try to open an async stream for
 					// the server to send notifications and requests out-of-band.
 
diff --git a/mcp/src/main/java/io/modelcontextprotocol/server/transport/HttpServletStreamableServerTransportProvider.java b/mcp/src/main/java/io/modelcontextprotocol/server/transport/HttpServletStreamableServerTransportProvider.java
index 8b95ec60..419238d1 100644
--- a/mcp/src/main/java/io/modelcontextprotocol/server/transport/HttpServletStreamableServerTransportProvider.java
+++ b/mcp/src/main/java/io/modelcontextprotocol/server/transport/HttpServletStreamableServerTransportProvider.java
@@ -103,7 +103,7 @@ public class HttpServletStreamableServerTransportProvider extends HttpServlet
 	private McpStreamableServerSession.Factory sessionFactory;
 
 	/**
-	 * Map of active client sessions, keyed by mcp-session-id.
+	 * Map of active client sessions, keyed by Mcp-Session-Id.
 	 */
 	private final ConcurrentHashMap<String, McpStreamableServerSession> sessions = new ConcurrentHashMap<>();
 
@@ -256,7 +256,7 @@ protected void doGet(HttpServletRequest request, HttpServletResponse response)
 		String sessionId = request.getHeader(HttpHeaders.MCP_SESSION_ID);
 
 		if (sessionId == null || sessionId.isBlank()) {
-			badRequestErrors.add("Session ID required in mcp-session-id header");
+			badRequestErrors.add("Session ID required in " + HttpHeaders.MCP_SESSION_ID + " header");
 		}
 
 		if (!badRequestErrors.isEmpty()) {
@@ -438,7 +438,7 @@ protected void doPost(HttpServletRequest request, HttpServletResponse response)
 			String sessionId = request.getHeader(HttpHeaders.MCP_SESSION_ID);
 
 			if (sessionId == null || sessionId.isBlank()) {
-				badRequestErrors.add("Session ID required in mcp-session-id header");
+				badRequestErrors.add("Session ID required in " + HttpHeaders.MCP_SESSION_ID + " header");
 			}
 
 			if (!badRequestErrors.isEmpty()) {
@@ -545,7 +545,7 @@ protected void doDelete(HttpServletRequest request, HttpServletResponse response
 
 		if (request.getHeader(HttpHeaders.MCP_SESSION_ID) == null) {
 			this.responseError(response, HttpServletResponse.SC_BAD_REQUEST,
-					new McpError("Session ID required in mcp-session-id header"));
+					new McpError("Session ID required in " + HttpHeaders.MCP_SESSION_ID + " header"));
 			return;
 		}
 
diff --git a/mcp/src/main/java/io/modelcontextprotocol/spec/HttpHeaders.java b/mcp/src/main/java/io/modelcontextprotocol/spec/HttpHeaders.java
index 65b80957..370b4707 100644
--- a/mcp/src/main/java/io/modelcontextprotocol/spec/HttpHeaders.java
+++ b/mcp/src/main/java/io/modelcontextprotocol/spec/HttpHeaders.java
@@ -14,7 +14,7 @@ public interface HttpHeaders {
 	/**
 	 * Identifies individual MCP sessions.
 	 */
-	String MCP_SESSION_ID = "mcp-session-id";
+	String MCP_SESSION_ID = "Mcp-Session-Id";
 
 	/**
 	 * Identifies events within an SSE Stream.