diff --git a/dist/index.cjs b/dist/index.cjs
index 1c43bac25a1037416fdf2ddfb4534ba0897a2e69..7e2108326f368ccbc48897195d57e370a4553855 100644
--- a/dist/index.cjs
+++ b/dist/index.cjs
@@ -3154,6 +3154,7 @@ var Client = class extends require_src.Protocol {
 	*/
 	async _connectPlainLegacy(transport, options) {
 		await super.connect(transport);
+		transport.onsessionexpired = () => this._legacyHandshake(transport, options);
 		if (transport.sessionId !== void 0) {
 			const negotiatedProtocolVersion = this._negotiatedProtocolVersion;
 			if (negotiatedProtocolVersion !== void 0) transport.setProtocolVersion?.(negotiatedProtocolVersion);
@@ -3170,6 +3171,7 @@ var Client = class extends require_src.Protocol {
 	* the handshake; its completion sets the negotiated (legacy) version.
 	*/
 	async _legacyHandshake(transport, options) {
+		transport.onsessionexpired = () => this._legacyHandshake(transport, options);
 		const legacyVersions = require_src.legacyProtocolVersions(this._supportedProtocolVersions);
 		try {
 			const offeredVersion = legacyVersions[0];
@@ -3208,6 +3210,7 @@ var Client = class extends require_src.Protocol {
 			await super.connect(transport);
 			const negotiatedProtocolVersion = this._negotiatedProtocolVersion;
 			if (negotiatedProtocolVersion !== void 0 && transport.setProtocolVersion) transport.setProtocolVersion(negotiatedProtocolVersion);
+			if (negotiatedProtocolVersion !== void 0 && !require_src.isModernProtocolVersion(negotiatedProtocolVersion)) transport.onsessionexpired = () => this._legacyHandshake(transport, options);
 			return;
 		}
 		this._resetConnectionState();
@@ -5211,10 +5214,32 @@ var StreamableHTTPClientTransport = class {
 		}
 	}
 	async send(message, options) {
-		return this._send(message, options, false);
+		return this._send(message, options, false, 0, false);
+	}
+	async _recoverSession(expiredSessionId) {
+		if (this._sessionRecovery) return this._sessionRecovery;
+		if (!this.onsessionexpired) return false;
+		if (this._sessionId !== expiredSessionId) return true;
+		this._sessionId = void 0;
+		this._sessionRecovery = Promise.resolve().then(() => this.onsessionexpired()).then(() => true);
+		try {
+			return await this._sessionRecovery;
+		} catch (error) {
+			this._sessionId = void 0;
+			await this.close();
+			throw error;
+		} finally {
+			this._sessionRecovery = void 0;
+		}
 	}
-	async _send(message, options, isAuthRetry, stepUpRetries = 0) {
+	async _send(message, options, isAuthRetry, stepUpRetries = 0, isSessionRetry = false) {
 		try {
+			const isHandshake = Array.isArray(message) ? message.some((m) => require_src.isInitializeRequest(m)) : require_src.isInitializeRequest(message);
+			const isInitialized = Array.isArray(message) ? message.some((m) => require_src.isInitializedNotification(m)) : require_src.isInitializedNotification(message);
+			if (this._sessionRecovery && !isHandshake && !isInitialized) {
+				await this._sessionRecovery;
+				options?.requestSignal?.throwIfAborted();
+			}
 			const { resumptionToken, onresumptiontoken } = options || {};
 			if (resumptionToken) {
 				this._startOrAuthSse({
@@ -5226,8 +5251,8 @@ var StreamableHTTPClientTransport = class {
 			}
 			const headers = await this._commonHeaders();
 			this._applyBodyDerivedHeaders(headers, message);
-			const isHandshake = Array.isArray(message) ? message.some((m) => require_src.isInitializeRequest(m)) : require_src.isInitializeRequest(message);
 			if (isHandshake) headers.delete("mcp-session-id");
+			const requestSessionId = headers.get("mcp-session-id") || void 0;
 			if (options?.headers !== void 0) for (const [name, value] of Object.entries(options.headers)) {
 				if (RESERVED_REQUEST_HEADER_NAMES.has(name.toLowerCase())) continue;
 				headers.set(name, value);
@@ -5249,8 +5274,14 @@ var StreamableHTTPClientTransport = class {
 				signal
 			};
 			const response = await (this._fetch ?? fetch)(this._url, init);
-			if (isHandshake && response.ok) this._sessionId = response.headers.get("mcp-session-id") || void 0;
+			if (isHandshake && response.ok && (requestSessionId === void 0 || this._sessionId === requestSessionId)) this._sessionId = response.headers.get("mcp-session-id") || void 0;
 			if (!response.ok) {
+				if (response.status === 404 && requestSessionId && !isSessionRetry && !isInitialized) {
+					if (await this._recoverSession(requestSessionId)) {
+						options?.requestSignal?.throwIfAborted();
+						return this._send(message, options, isAuthRetry, stepUpRetries, true);
+					}
+				}
 				if (response.status === 401 && this._authProvider) {
 					if (response.headers.has("www-authenticate")) {
 						const { resourceMetadataUrl, scope } = extractWWWAuthenticateParams(response);
@@ -5264,7 +5295,7 @@ var StreamableHTTPClientTransport = class {
 							fetchFn: this._fetchWithInit
 						});
 						await response.text?.().catch(() => {});
-						return this._send(message, options, true, stepUpRetries);
+						return this._send(message, options, true, stepUpRetries, isSessionRetry);
 					}
 					await response.text?.().catch(() => {});
 					if (isAuthRetry) throw new require_src.SdkHttpError(require_src.SdkErrorCode.ClientHttpAuthentication, "Server returned 401 after re-authentication", {
@@ -5284,7 +5315,7 @@ var StreamableHTTPClientTransport = class {
 							statusText: response.statusText,
 							text
 						}, stepUpRetries) !== "AUTHORIZED") throw new UnauthorizedError();
-						return this._send(message, options, isAuthRetry, stepUpRetries + 1);
+						return this._send(message, options, isAuthRetry, stepUpRetries + 1, isSessionRetry);
 					}
 				}
 				if (response.status === 400 && typeof text === "string" && this._isModernEnvelopedRequest(message)) try {
diff --git a/dist/index.mjs b/dist/index.mjs
index 77e2389913cb5c5c2b047f95d990ab2892bef923..4b5e4ff2869189d600ca644488a7749668c39747 100644
--- a/dist/index.mjs
+++ b/dist/index.mjs
@@ -3151,6 +3151,7 @@ var Client = class extends Protocol {
 	*/
 	async _connectPlainLegacy(transport, options) {
 		await super.connect(transport);
+		transport.onsessionexpired = () => this._legacyHandshake(transport, options);
 		if (transport.sessionId !== void 0) {
 			const negotiatedProtocolVersion = this._negotiatedProtocolVersion;
 			if (negotiatedProtocolVersion !== void 0) transport.setProtocolVersion?.(negotiatedProtocolVersion);
@@ -3167,6 +3168,7 @@ var Client = class extends Protocol {
 	* the handshake; its completion sets the negotiated (legacy) version.
 	*/
 	async _legacyHandshake(transport, options) {
+		transport.onsessionexpired = () => this._legacyHandshake(transport, options);
 		const legacyVersions = legacyProtocolVersions(this._supportedProtocolVersions);
 		try {
 			const offeredVersion = legacyVersions[0];
@@ -3205,6 +3207,7 @@ var Client = class extends Protocol {
 			await super.connect(transport);
 			const negotiatedProtocolVersion = this._negotiatedProtocolVersion;
 			if (negotiatedProtocolVersion !== void 0 && transport.setProtocolVersion) transport.setProtocolVersion(negotiatedProtocolVersion);
+			if (negotiatedProtocolVersion !== void 0 && !isModernProtocolVersion(negotiatedProtocolVersion)) transport.onsessionexpired = () => this._legacyHandshake(transport, options);
 			return;
 		}
 		this._resetConnectionState();
@@ -5208,10 +5211,32 @@ var StreamableHTTPClientTransport = class {
 		}
 	}
 	async send(message, options) {
-		return this._send(message, options, false);
+		return this._send(message, options, false, 0, false);
+	}
+	async _recoverSession(expiredSessionId) {
+		if (this._sessionRecovery) return this._sessionRecovery;
+		if (!this.onsessionexpired) return false;
+		if (this._sessionId !== expiredSessionId) return true;
+		this._sessionId = void 0;
+		this._sessionRecovery = Promise.resolve().then(() => this.onsessionexpired()).then(() => true);
+		try {
+			return await this._sessionRecovery;
+		} catch (error) {
+			this._sessionId = void 0;
+			await this.close();
+			throw error;
+		} finally {
+			this._sessionRecovery = void 0;
+		}
 	}
-	async _send(message, options, isAuthRetry, stepUpRetries = 0) {
+	async _send(message, options, isAuthRetry, stepUpRetries = 0, isSessionRetry = false) {
 		try {
+			const isHandshake = Array.isArray(message) ? message.some((m) => isInitializeRequest(m)) : isInitializeRequest(message);
+			const isInitialized = Array.isArray(message) ? message.some((m) => isInitializedNotification(m)) : isInitializedNotification(message);
+			if (this._sessionRecovery && !isHandshake && !isInitialized) {
+				await this._sessionRecovery;
+				options?.requestSignal?.throwIfAborted();
+			}
 			const { resumptionToken, onresumptiontoken } = options || {};
 			if (resumptionToken) {
 				this._startOrAuthSse({
@@ -5223,8 +5248,8 @@ var StreamableHTTPClientTransport = class {
 			}
 			const headers = await this._commonHeaders();
 			this._applyBodyDerivedHeaders(headers, message);
-			const isHandshake = Array.isArray(message) ? message.some((m) => isInitializeRequest(m)) : isInitializeRequest(message);
 			if (isHandshake) headers.delete("mcp-session-id");
+			const requestSessionId = headers.get("mcp-session-id") || void 0;
 			if (options?.headers !== void 0) for (const [name, value] of Object.entries(options.headers)) {
 				if (RESERVED_REQUEST_HEADER_NAMES.has(name.toLowerCase())) continue;
 				headers.set(name, value);
@@ -5246,8 +5271,14 @@ var StreamableHTTPClientTransport = class {
 				signal
 			};
 			const response = await (this._fetch ?? fetch)(this._url, init);
-			if (isHandshake && response.ok) this._sessionId = response.headers.get("mcp-session-id") || void 0;
+			if (isHandshake && response.ok && (requestSessionId === void 0 || this._sessionId === requestSessionId)) this._sessionId = response.headers.get("mcp-session-id") || void 0;
 			if (!response.ok) {
+				if (response.status === 404 && requestSessionId && !isSessionRetry && !isInitialized) {
+					if (await this._recoverSession(requestSessionId)) {
+						options?.requestSignal?.throwIfAborted();
+						return this._send(message, options, isAuthRetry, stepUpRetries, true);
+					}
+				}
 				if (response.status === 401 && this._authProvider) {
 					if (response.headers.has("www-authenticate")) {
 						const { resourceMetadataUrl, scope } = extractWWWAuthenticateParams(response);
@@ -5261,7 +5292,7 @@ var StreamableHTTPClientTransport = class {
 							fetchFn: this._fetchWithInit
 						});
 						await response.text?.().catch(() => {});
-						return this._send(message, options, true, stepUpRetries);
+						return this._send(message, options, true, stepUpRetries, isSessionRetry);
 					}
 					await response.text?.().catch(() => {});
 					if (isAuthRetry) throw new SdkHttpError(SdkErrorCode.ClientHttpAuthentication, "Server returned 401 after re-authentication", {
@@ -5281,7 +5312,7 @@ var StreamableHTTPClientTransport = class {
 							statusText: response.statusText,
 							text
 						}, stepUpRetries) !== "AUTHORIZED") throw new UnauthorizedError();
-						return this._send(message, options, isAuthRetry, stepUpRetries + 1);
+						return this._send(message, options, isAuthRetry, stepUpRetries + 1, isSessionRetry);
 					}
 				}
 				if (response.status === 400 && typeof text === "string" && this._isModernEnvelopedRequest(message)) try {