diff --git a/src/client/streamableHttp.test.ts b/src/client/streamableHttp.test.ts
new file mode 100644
index 000000000..0dc582d46
--- /dev/null
+++ b/src/client/streamableHttp.test.ts
@@ -0,0 +1,316 @@
+import { StreamableHTTPClientTransport } from "./streamableHttp.js";
+import { JSONRPCMessage } from "../types.js";
+
+
+describe("StreamableHTTPClientTransport", () => {
+  let transport: StreamableHTTPClientTransport;
+
+  beforeEach(() => {
+    transport = new StreamableHTTPClientTransport(new URL("http://localhost:1234/mcp"));
+    jest.spyOn(global, "fetch");
+  });
+
+  afterEach(async () => {
+    await transport.close().catch(() => { });
+    jest.clearAllMocks();
+  });
+
+  it("should send JSON-RPC messages via POST", async () => {
+    const message: JSONRPCMessage = {
+      jsonrpc: "2.0",
+      method: "test",
+      params: {},
+      id: "test-id"
+    };
+
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      status: 202,
+      headers: new Headers(),
+    });
+
+    await transport.send(message);
+
+    expect(global.fetch).toHaveBeenCalledWith(
+      expect.anything(),
+      expect.objectContaining({
+        method: "POST",
+        headers: expect.any(Headers),
+        body: JSON.stringify(message)
+      })
+    );
+  });
+
+  it("should send batch messages", async () => {
+    const messages: JSONRPCMessage[] = [
+      { jsonrpc: "2.0", method: "test1", params: {}, id: "id1" },
+      { jsonrpc: "2.0", method: "test2", params: {}, id: "id2" }
+    ];
+
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      status: 200,
+      headers: new Headers({ "content-type": "text/event-stream" }),
+      body: null
+    });
+
+    await transport.send(messages);
+
+    expect(global.fetch).toHaveBeenCalledWith(
+      expect.anything(),
+      expect.objectContaining({
+        method: "POST",
+        headers: expect.any(Headers),
+        body: JSON.stringify(messages)
+      })
+    );
+  });
+
+  it("should store session ID received during initialization", async () => {
+    const message: JSONRPCMessage = {
+      jsonrpc: "2.0",
+      method: "initialize",
+      params: {
+        clientInfo: { name: "test-client", version: "1.0" },
+        protocolVersion: "2025-03-26"
+      },
+      id: "init-id"
+    };
+
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      status: 200,
+      headers: new Headers({ "mcp-session-id": "test-session-id" }),
+    });
+
+    await transport.send(message);
+
+    // Send a second message that should include the session ID
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      status: 202,
+      headers: new Headers()
+    });
+
+    await transport.send({ jsonrpc: "2.0", method: "test", params: {} } as JSONRPCMessage);
+
+    // Check that second request included session ID header
+    const calls = (global.fetch as jest.Mock).mock.calls;
+    const lastCall = calls[calls.length - 1];
+    expect(lastCall[1].headers).toBeDefined();
+    expect(lastCall[1].headers.get("mcp-session-id")).toBe("test-session-id");
+  });
+
+  it("should handle 404 response when session expires", async () => {
+    const message: JSONRPCMessage = {
+      jsonrpc: "2.0",
+      method: "test",
+      params: {},
+      id: "test-id"
+    };
+
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: false,
+      status: 404,
+      statusText: "Not Found",
+      text: () => Promise.resolve("Session not found"),
+      headers: new Headers()
+    });
+
+    const errorSpy = jest.fn();
+    transport.onerror = errorSpy;
+
+    await expect(transport.send(message)).rejects.toThrow("Error POSTing to endpoint (HTTP 404)");
+    expect(errorSpy).toHaveBeenCalled();
+  });
+
+  it("should handle non-streaming JSON response", async () => {
+    const message: JSONRPCMessage = {
+      jsonrpc: "2.0",
+      method: "test",
+      params: {},
+      id: "test-id"
+    };
+
+    const responseMessage: JSONRPCMessage = {
+      jsonrpc: "2.0",
+      result: { success: true },
+      id: "test-id"
+    };
+
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      status: 200,
+      headers: new Headers({ "content-type": "application/json" }),
+      json: () => Promise.resolve(responseMessage)
+    });
+
+    const messageSpy = jest.fn();
+    transport.onmessage = messageSpy;
+
+    await transport.send(message);
+
+    expect(messageSpy).toHaveBeenCalledWith(responseMessage);
+  });
+
+  it("should attempt initial GET connection and handle 405 gracefully", async () => {
+    // Mock the server not supporting GET for SSE (returning 405)
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: false,
+      status: 405,
+      statusText: "Method Not Allowed"
+    });
+
+    // We expect the 405 error to be caught and handled gracefully
+    // This should not throw an error that breaks the transport
+    await transport.start();
+    await expect(transport.openSseStream()).rejects.toThrow('Failed to open SSE stream: Method Not Allowed');
+
+    // Check that GET was attempted
+    expect(global.fetch).toHaveBeenCalledWith(
+      expect.anything(),
+      expect.objectContaining({
+        method: "GET",
+        headers: expect.any(Headers)
+      })
+    );
+
+    // Verify transport still works after 405
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      status: 202,
+      headers: new Headers()
+    });
+
+    await transport.send({ jsonrpc: "2.0", method: "test", params: {} } as JSONRPCMessage);
+    expect(global.fetch).toHaveBeenCalledTimes(2);
+  });
+
+  it("should handle successful initial GET connection for SSE", async () => {
+    // Set up readable stream for SSE events
+    const encoder = new TextEncoder();
+    const stream = new ReadableStream({
+      start(controller) {
+        // Send a server notification via SSE
+        const event = 'event: message\ndata: {"jsonrpc": "2.0", "method": "serverNotification", "params": {}}\n\n';
+        controller.enqueue(encoder.encode(event));
+      }
+    });
+
+    // Mock successful GET connection
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      status: 200,
+      headers: new Headers({ "content-type": "text/event-stream" }),
+      body: stream
+    });
+
+    const messageSpy = jest.fn();
+    transport.onmessage = messageSpy;
+
+    await transport.start();
+    await transport.openSseStream();
+
+    // Give time for the SSE event to be processed
+    await new Promise(resolve => setTimeout(resolve, 50));
+
+    expect(messageSpy).toHaveBeenCalledWith(
+      expect.objectContaining({
+        jsonrpc: "2.0",
+        method: "serverNotification",
+        params: {}
+      })
+    );
+  });
+
+  it("should handle multiple concurrent SSE streams", async () => {
+    // Mock two POST requests that return SSE streams
+    const makeStream = (id: string) => {
+      const encoder = new TextEncoder();
+      return new ReadableStream({
+        start(controller) {
+          const event = `event: message\ndata: {"jsonrpc": "2.0", "result": {"id": "${id}"}, "id": "${id}"}\n\n`;
+          controller.enqueue(encoder.encode(event));
+        }
+      });
+    };
+
+    (global.fetch as jest.Mock)
+      .mockResolvedValueOnce({
+        ok: true, 
+        status: 200,
+        headers: new Headers({ "content-type": "text/event-stream" }),
+        body: makeStream("request1")
+      })
+      .mockResolvedValueOnce({
+        ok: true,
+        status: 200,
+        headers: new Headers({ "content-type": "text/event-stream" }),
+        body: makeStream("request2")
+      });
+
+    const messageSpy = jest.fn();
+    transport.onmessage = messageSpy;
+
+    // Send two concurrent requests
+    await Promise.all([
+      transport.send({ jsonrpc: "2.0", method: "test1", params: {}, id: "request1" }),
+      transport.send({ jsonrpc: "2.0", method: "test2", params: {}, id: "request2" })
+    ]);
+
+    // Give time for SSE processing
+    await new Promise(resolve => setTimeout(resolve, 100));
+
+    // Both streams should have delivered their messages
+    expect(messageSpy).toHaveBeenCalledTimes(2);
+    
+    // Verify received messages without assuming specific order
+    expect(messageSpy.mock.calls.some(call => {
+      const msg = call[0];
+      return msg.id === "request1" && msg.result?.id === "request1";
+    })).toBe(true);
+    
+    expect(messageSpy.mock.calls.some(call => {
+      const msg = call[0];
+      return msg.id === "request2" && msg.result?.id === "request2";
+    })).toBe(true);
+  });
+
+  it("should include last-event-id header when resuming a broken connection", async () => {
+    // First make a successful connection that provides an event ID
+    const encoder = new TextEncoder();
+    const stream = new ReadableStream({
+      start(controller) {
+        const event = 'id: event-123\nevent: message\ndata: {"jsonrpc": "2.0", "method": "serverNotification", "params": {}}\n\n';
+        controller.enqueue(encoder.encode(event));
+        controller.close();
+      }
+    });
+
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      status: 200,
+      headers: new Headers({ "content-type": "text/event-stream" }),
+      body: stream
+    });
+
+    await transport.start();
+    await transport.openSseStream();
+    await new Promise(resolve => setTimeout(resolve, 50));
+
+    // Now simulate attempting to reconnect
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      status: 200,
+      headers: new Headers({ "content-type": "text/event-stream" }),
+      body: null
+    });
+
+    await transport.openSseStream();
+
+    // Check that Last-Event-ID was included
+    const calls = (global.fetch as jest.Mock).mock.calls;
+    const lastCall = calls[calls.length - 1];
+    expect(lastCall[1].headers.get("last-event-id")).toBe("event-123");
+  });
+});
\ No newline at end of file
diff --git a/src/client/streamableHttp.ts b/src/client/streamableHttp.ts
new file mode 100644
index 000000000..0c667e35b
--- /dev/null
+++ b/src/client/streamableHttp.ts
@@ -0,0 +1,312 @@
+import { Transport } from "../shared/transport.js";
+import { JSONRPCMessage, JSONRPCMessageSchema } from "../types.js";
+import { auth, AuthResult, OAuthClientProvider, UnauthorizedError } from "./auth.js";
+import { EventSourceParserStream } from 'eventsource-parser/stream';
+export class StreamableHTTPError extends Error {
+  constructor(
+    public readonly code: number | undefined,
+    message: string | undefined,
+  ) {
+    super(`Streamable HTTP error: ${message}`);
+  }
+}
+
+/**
+ * Configuration options for the `StreamableHTTPClientTransport`.
+ */
+export type StreamableHTTPClientTransportOptions = {
+  /**
+   * An OAuth client provider to use for authentication.
+   * 
+   * When an `authProvider` is specified and the connection is started:
+   * 1. The connection is attempted with any existing access token from the `authProvider`.
+   * 2. If the access token has expired, the `authProvider` is used to refresh the token.
+   * 3. If token refresh fails or no access token exists, and auth is required, `OAuthClientProvider.redirectToAuthorization` is called, and an `UnauthorizedError` will be thrown from `connect`/`start`.
+   * 
+   * After the user has finished authorizing via their user agent, and is redirected back to the MCP client application, call `StreamableHTTPClientTransport.finishAuth` with the authorization code before retrying the connection.
+   * 
+   * If an `authProvider` is not provided, and auth is required, an `UnauthorizedError` will be thrown.
+   * 
+   * `UnauthorizedError` might also be thrown when sending any message over the transport, indicating that the session has expired, and needs to be re-authed and reconnected.
+   */
+  authProvider?: OAuthClientProvider;
+
+  /**
+   * Customizes HTTP requests to the server.
+   */
+  requestInit?: RequestInit;
+};
+
+/**
+ * Client transport for Streamable HTTP: this implements the MCP Streamable HTTP transport specification.
+ * It will connect to a server using HTTP POST for sending messages and HTTP GET with Server-Sent Events
+ * for receiving messages.
+ */
+export class StreamableHTTPClientTransport implements Transport {
+  private _abortController?: AbortController;
+  private _url: URL;
+  private _requestInit?: RequestInit;
+  private _authProvider?: OAuthClientProvider;
+  private _sessionId?: string;
+  private _lastEventId?: string;
+
+  onclose?: () => void;
+  onerror?: (error: Error) => void;
+  onmessage?: (message: JSONRPCMessage) => void;
+
+  constructor(
+    url: URL,
+    opts?: StreamableHTTPClientTransportOptions,
+  ) {
+    this._url = url;
+    this._requestInit = opts?.requestInit;
+    this._authProvider = opts?.authProvider;
+  }
+
+  private async _authThenStart(): Promise<void> {
+    if (!this._authProvider) {
+      throw new UnauthorizedError("No auth provider");
+    }
+
+    let result: AuthResult;
+    try {
+      result = await auth(this._authProvider, { serverUrl: this._url });
+    } catch (error) {
+      this.onerror?.(error as Error);
+      throw error;
+    }
+
+    if (result !== "AUTHORIZED") {
+      throw new UnauthorizedError();
+    }
+
+    return await this._startOrAuthStandaloneSSE();
+  }
+
+  private async _commonHeaders(): Promise<HeadersInit> {
+    const headers: HeadersInit = {};
+    if (this._authProvider) {
+      const tokens = await this._authProvider.tokens();
+      if (tokens) {
+        headers["Authorization"] = `Bearer ${tokens.access_token}`;
+      }
+    }
+
+    if (this._sessionId) {
+      headers["mcp-session-id"] = this._sessionId;
+    }
+
+    return headers;
+  }
+
+  private async _startOrAuthStandaloneSSE(): Promise<void> {
+    try {
+      // Try to open an initial SSE stream with GET to listen for server messages
+      // This is optional according to the spec - server may not support it
+      const commonHeaders = await this._commonHeaders();
+      const headers = new Headers(commonHeaders);
+      headers.set('Accept', 'text/event-stream');
+
+      // Include Last-Event-ID header for resumable streams
+      if (this._lastEventId) {
+        headers.set('last-event-id', this._lastEventId);
+      }
+
+      const response = await fetch(this._url, {
+        method: 'GET',
+        headers,
+        signal: this._abortController?.signal,
+      });
+
+      if (!response.ok) {
+        if (response.status === 401 && this._authProvider) {
+          // Need to authenticate
+          return await this._authThenStart();
+        }
+
+        const error = new StreamableHTTPError(
+          response.status,
+          `Failed to open SSE stream: ${response.statusText}`,
+        );
+        this.onerror?.(error);
+        throw error;
+      }
+
+      // Successful connection, handle the SSE stream as a standalone listener
+      this._handleSseStream(response.body);
+    } catch (error) {
+      this.onerror?.(error as Error);
+      throw error;
+    }
+  }
+
+  private _handleSseStream(stream: ReadableStream<Uint8Array> | null): void {
+    if (!stream) {
+      return;
+    }
+    // Create a pipeline: binary stream -> text decoder -> SSE parser
+    const eventStream = stream
+      .pipeThrough(new TextDecoderStream())
+      .pipeThrough(new EventSourceParserStream());
+
+    const reader = eventStream.getReader();
+    const processStream = async () => {
+      try {
+        while (true) {
+          const { done, value: event } = await reader.read();
+          if (done) {
+            break;
+          }
+
+          // Update last event ID if provided
+          if (event.id) {
+            this._lastEventId = event.id;
+          }
+
+          // Handle message events (default event type is undefined per docs)
+          // or explicit 'message' event type
+          if (!event.event || event.event === 'message') {
+            try {
+              const message = JSONRPCMessageSchema.parse(JSON.parse(event.data));
+              this.onmessage?.(message);
+            } catch (error) {
+              this.onerror?.(error as Error);
+            }
+          }
+        }
+      } catch (error) {
+        this.onerror?.(error as Error);
+      }
+    };
+
+    processStream();
+  }
+
+  async start() {
+    if (this._abortController) {
+      throw new Error(
+        "StreamableHTTPClientTransport already started! If using Client class, note that connect() calls start() automatically.",
+      );
+    }
+
+    this._abortController = new AbortController();
+  }
+
+  /**
+   * Call this method after the user has finished authorizing via their user agent and is redirected back to the MCP client application. This will exchange the authorization code for an access token, enabling the next connection attempt to successfully auth.
+   */
+  async finishAuth(authorizationCode: string): Promise<void> {
+    if (!this._authProvider) {
+      throw new UnauthorizedError("No auth provider");
+    }
+
+    const result = await auth(this._authProvider, { serverUrl: this._url, authorizationCode });
+    if (result !== "AUTHORIZED") {
+      throw new UnauthorizedError("Failed to authorize");
+    }
+  }
+
+  async close(): Promise<void> {
+    // Abort any pending requests
+    this._abortController?.abort();
+
+    this.onclose?.();
+  }
+
+  async send(message: JSONRPCMessage | JSONRPCMessage[]): Promise<void> {
+    try {
+      const commonHeaders = await this._commonHeaders();
+      const headers = new Headers({ ...commonHeaders, ...this._requestInit?.headers });
+      headers.set("content-type", "application/json");
+      headers.set("accept", "application/json, text/event-stream");
+
+      const init = {
+        ...this._requestInit,
+        method: "POST",
+        headers,
+        body: JSON.stringify(message),
+        signal: this._abortController?.signal,
+      };
+
+      const response = await fetch(this._url, init);
+
+      // Handle session ID received during initialization
+      const sessionId = response.headers.get("mcp-session-id");
+      if (sessionId) {
+        this._sessionId = sessionId;
+      }
+
+      if (!response.ok) {
+        if (response.status === 401 && this._authProvider) {
+          const result = await auth(this._authProvider, { serverUrl: this._url });
+          if (result !== "AUTHORIZED") {
+            throw new UnauthorizedError();
+          }
+
+          // Purposely _not_ awaited, so we don't call onerror twice
+          return this.send(message);
+        }
+
+        const text = await response.text().catch(() => null);
+        throw new Error(
+          `Error POSTing to endpoint (HTTP ${response.status}): ${text}`,
+        );
+      }
+
+      // If the response is 202 Accepted, there's no body to process
+      if (response.status === 202) {
+        return;
+      }
+
+      // Get original message(s) for detecting request IDs
+      const messages = Array.isArray(message) ? message : [message];
+
+      // Extract IDs from request messages for tracking responses
+      const requestIds = messages.filter(msg => 'method' in msg && 'id' in msg)
+        .map(msg => 'id' in msg ? msg.id : undefined)
+        .filter(id => id !== undefined);
+
+      // If we have request IDs and an SSE response, create a unique stream ID
+      const hasRequests = requestIds.length > 0;
+
+      // Check the response type
+      const contentType = response.headers.get("content-type");
+
+      if (hasRequests) {
+        if (contentType?.includes("text/event-stream")) {
+          // For streaming responses, create a unique stream ID based on request IDs
+          this._handleSseStream(response.body);
+        } else if (contentType?.includes("application/json")) {
+          // For non-streaming servers, we might get direct JSON responses
+          const data = await response.json();
+          const responseMessages = Array.isArray(data)
+            ? data.map(msg => JSONRPCMessageSchema.parse(msg))
+            : [JSONRPCMessageSchema.parse(data)];
+
+          for (const msg of responseMessages) {
+            this.onmessage?.(msg);
+          }
+        }
+      }
+    } catch (error) {
+      this.onerror?.(error as Error);
+      throw error;
+    }
+  }
+
+  /**
+   * Opens SSE stream to receive messages from the server.
+   * 
+   * This allows the server to push messages to the client without requiring the client
+   * to first send a request via HTTP POST. Some servers may not support this feature.
+   * If authentication is required but fails, this method will throw an UnauthorizedError.
+   */
+  async openSseStream(): Promise<void> {
+    if (!this._abortController) {
+      throw new Error(
+        "StreamableHTTPClientTransport not started! Call connect() before openSseStream().",
+      );
+    }
+    await this._startOrAuthStandaloneSSE();
+  }
+}
\ No newline at end of file