diff --git a/README.md b/README.md
index a7dc6927..d1db291d 100644
--- a/README.md
+++ b/README.md
@@ -148,7 +148,7 @@ server.notify_tools_list_changed()
 #### Rails Controller
 
 When added to a Rails controller on a route that handles POST requests, your server will be compliant with non-streaming
-[Streamable HTTP](https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http) transport
+[Streamable HTTP](https://modelcontextprotocol.io/specification/2025-06-18/basic/transports#streamable-http) transport
 requests.
 
 You can use the `Server#handle_json` method to handle requests.
@@ -340,7 +340,7 @@ MCP::Server.protocol_version = nil
 
 If an invalid `protocol_version` value is set, an `ArgumentError` is raised.
 
-Be sure to check the [MCP spec](https://modelcontextprotocol.io/specification/2025-03-26) for the protocol version to understand the supported features for the version being set.
+Be sure to check the [MCP spec](https://modelcontextprotocol.io/specification) for the protocol version to understand the supported features for the version being set.
 
 ### Exception Reporting
 
diff --git a/lib/mcp/configuration.rb b/lib/mcp/configuration.rb
index 038be59a..30dcc5a6 100644
--- a/lib/mcp/configuration.rb
+++ b/lib/mcp/configuration.rb
@@ -2,8 +2,8 @@
 
 module MCP
   class Configuration
-    DEFAULT_PROTOCOL_VERSION = "2024-11-05"
-    SUPPORTED_PROTOCOL_VERSIONS = ["2025-06-18", "2025-03-26", DEFAULT_PROTOCOL_VERSION]
+    DEFAULT_PROTOCOL_VERSION = "2025-06-18"
+    SUPPORTED_PROTOCOL_VERSIONS = [DEFAULT_PROTOCOL_VERSION, "2025-03-26", "2024-11-05"]
 
     attr_writer :exception_reporter, :instrumentation_callback, :protocol_version, :validate_tool_call_arguments
 
diff --git a/test/mcp/server/transports/streamable_http_transport_test.rb b/test/mcp/server/transports/streamable_http_transport_test.rb
index 2e86696c..34cd529c 100644
--- a/test/mcp/server/transports/streamable_http_transport_test.rb
+++ b/test/mcp/server/transports/streamable_http_transport_test.rb
@@ -84,7 +84,7 @@ class StreamableHTTPTransportTest < ActiveSupport::TestCase
           body = JSON.parse(response[2][0])
           assert_equal "2.0", body["jsonrpc"]
           assert_equal "123", body["id"]
-          assert_equal "2024-11-05", body["result"]["protocolVersion"]
+          assert_equal "2025-06-18", body["result"]["protocolVersion"]
         end
 
         test "handles GET request with valid session ID" do
diff --git a/test/mcp/server_test.rb b/test/mcp/server_test.rb
index e1b12d34..3e5853f0 100644
--- a/test/mcp/server_test.rb
+++ b/test/mcp/server_test.rb
@@ -114,7 +114,7 @@ class ServerTest < ActiveSupport::TestCase
         jsonrpc: "2.0",
         id: 1,
         result: {
-          protocolVersion: "2024-11-05",
+          protocolVersion: "2025-06-18",
           capabilities: {
             prompts: { listChanged: true },
             resources: { listChanged: true },