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Merge pull request modelcontextprotocol#476 from koic/support_2026_07_28_as_latest_protocol_version
Support 2026-07-28 as the Latest Protocol Version
2 parents ba88d9f + dc25610 commit d20eac0

6 files changed

Lines changed: 60 additions & 16 deletions

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‎conformance/expected_failures.yml‎

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@@ -1,2 +1,6 @@
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server: []
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client: []
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client:
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# TODO: The conformance framework's client-initialization check pins the expected requested version to 2025-11-25,
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# while this SDK's latest protocol version is 2026-07-28. Remove once the @modelcontextprotocol/conformance package
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# accepts 2026-07-28.
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- initialize

‎docs/building-clients.md‎

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@@ -22,7 +22,7 @@ Call `MCP::Client#connect` to perform the MCP [initialization handshake](https:/
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```ruby
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client.connect
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# => { "protocolVersion" => "2025-11-25", "capabilities" => {...}, "serverInfo" => {...} }
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# => { "protocolVersion" => "2026-07-28", "capabilities" => {...}, "serverInfo" => {...} }
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client.connected? # => true
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client.server_info # => cached InitializeResult
@@ -99,7 +99,7 @@ After `connect` succeeds, the HTTP transport captures the `Mcp-Session-Id` heade
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```ruby
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http_transport.session_id # => "abc123..."
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http_transport.protocol_version # => "2025-11-25"
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http_transport.protocol_version # => "2026-07-28"
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```
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If the server terminates the session, subsequent requests return HTTP 404 and the transport raises `MCP::Client::SessionExpiredError` (a subclass of `RequestHandlerError`). Session state is cleared automatically; callers should start a new session by calling `connect` again.

‎lib/mcp/configuration.rb‎

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@@ -2,16 +2,17 @@
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module MCP
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class Configuration
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LATEST_STABLE_PROTOCOL_VERSION = "2025-11-25"
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LATEST_STABLE_PROTOCOL_VERSION = "2026-07-28"
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SUPPORTED_STABLE_PROTOCOL_VERSIONS = [
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LATEST_STABLE_PROTOCOL_VERSION, "2025-06-18", "2025-03-26", "2024-11-05",
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LATEST_STABLE_PROTOCOL_VERSION, "2025-11-25", "2025-06-18", "2025-03-26", "2024-11-05",
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].freeze
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DEFAULT_NEGOTIATED_PROTOCOL_VERSION = "2025-03-26"
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# Protocol versions of the stateless "modern" lifecycle introduced by the MCP 2026-07-28 spec release (SEP-2575).
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# Modern versions are deliberately kept out of `SUPPORTED_STABLE_PROTOCOL_VERSIONS`: the modern lifecycle has
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# no `initialize` handshake, so these versions are never negotiated (each request carries its own version in `_meta`
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# and is validated against this list independently), and `protocol_version=` keeps rejecting them for the same reason.
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# 2026-07-28 serves both lifecycles of the dual-era model: it is negotiable through the legacy `initialize`
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# handshake (so it also appears in `SUPPORTED_STABLE_PROTOCOL_VERSIONS`), and it is the version of the modern
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# lifecycle, where each request carries its own version in `_meta` and is validated against this list
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# independently, with no handshake.
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# https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2575
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LATEST_MODERN_PROTOCOL_VERSION = "2026-07-28"
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SUPPORTED_MODERN_PROTOCOL_VERSIONS = [LATEST_MODERN_PROTOCOL_VERSION].freeze

‎test/mcp/configuration_test.rb‎

Lines changed: 7 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -54,7 +54,7 @@ class ConfigurationTest < ActiveSupport::TestCase
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Configuration.new(protocol_version: "DRAFT-2025-v3")
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end
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57-
assert_equal("protocol_version must be 2025-11-25, 2025-06-18, 2025-03-26, or 2024-11-05", exception.message)
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assert_equal("protocol_version must be 2026-07-28, 2025-11-25, 2025-06-18, 2025-03-26, or 2024-11-05", exception.message)
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end
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test "raises ArgumentError when protocol_version is not a supported protocol version" do
@@ -63,7 +63,7 @@ class ConfigurationTest < ActiveSupport::TestCase
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custom_version = "2025-03-27"
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config.protocol_version = custom_version
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end
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assert_equal("protocol_version must be 2025-11-25, 2025-06-18, 2025-03-26, or 2024-11-05", exception.message)
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assert_equal("protocol_version must be 2026-07-28, 2025-11-25, 2025-06-18, 2025-03-26, or 2024-11-05", exception.message)
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end
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test "exposes the SEP-2575 modern protocol versions" do
@@ -73,12 +73,11 @@ class ConfigurationTest < ActiveSupport::TestCase
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refute Configuration.modern_protocol_version?("2025-11-25")
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end
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test "raises ArgumentError when setting a modern protocol version" do
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# Modern versions (SEP-2575) are never negotiated via `initialize`, so they are deliberately not settable as
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# the legacy fallback version.
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assert_raises(ArgumentError) do
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Configuration.new(protocol_version: Configuration::LATEST_MODERN_PROTOCOL_VERSION)
81-
end
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test "accepts 2026-07-28 as the protocol version" do
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# 2026-07-28 serves both lifecycles of the dual-era model (SEP-2575), so it is negotiable through
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# the legacy `initialize` handshake and settable as the fallback version.
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config = Configuration.new(protocol_version: Configuration::LATEST_MODERN_PROTOCOL_VERSION)
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assert_equal "2026-07-28", config.protocol_version
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end
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test "raises ArgumentError when protocol_version is not a boolean value" do

‎test/mcp/server/transports/streamable_http_transport_test.rb‎

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@@ -1993,6 +1993,32 @@ def string
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assert_equal 200, response[0]
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end
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test "POST request with the 2026-07-28 MCP-Protocol-Version header succeeds" do
1997+
init_request = create_rack_request(
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"POST",
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"/",
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{ "CONTENT_TYPE" => "application/json" },
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{ jsonrpc: "2.0", method: "initialize", id: "init", params: initialize_params(protocolVersion: "2026-07-28") }.to_json,
2002+
)
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init_response = @transport.handle_request(init_request)
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assert_equal "2026-07-28", JSON.parse(init_response[2][0])["result"]["protocolVersion"]
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session_id = init_response[1]["mcp-session-id"]
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request = create_rack_request(
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"POST",
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"/",
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{
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"CONTENT_TYPE" => "application/json",
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"HTTP_MCP_SESSION_ID" => session_id,
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"HTTP_MCP_PROTOCOL_VERSION" => "2026-07-28",
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},
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{ jsonrpc: "2.0", method: "tools/list", id: "list" }.to_json,
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)
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response = @transport.handle_request(request)
2019+
assert_equal 200, response[0]
2020+
end
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test "POST request without MCP-Protocol-Version header succeeds" do
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init_request = create_rack_request(
19982024
"POST",

‎test/mcp/server_test.rb‎

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@@ -2036,6 +2036,20 @@ def read_resource_request(uri)
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assert_equal Configuration::LATEST_STABLE_PROTOCOL_VERSION, response[:result][:protocolVersion]
20372037
end
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2039+
test "server negotiates 2026-07-28 when the client requests it via initialize" do
2040+
server = Server.new(name: "test_server")
2041+
2042+
request = {
2043+
jsonrpc: "2.0",
2044+
method: "initialize",
2045+
id: 1,
2046+
params: initialize_params(protocolVersion: "2026-07-28"),
2047+
}
2048+
2049+
response = server.handle(request)
2050+
assert_equal "2026-07-28", response[:result][:protocolVersion]
2051+
end
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test "server removes description and icons from server_info when negotiating to 2025-06-18" do
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server = Server.new(
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name: "test_server",

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