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[Discussion] MCP Version 2026-07-28 Support for AI workspace and AI Gateway #3385
Replies: 11 comments
MCP Version 2026-07-28Unlike previous MCP versions, which began a conversation with an initialization handshake and maintained context through a server-assigned session, MCP 2026-07-28 is stateless. Each request carries all the information required for processing, and the server does not retain session state between requests.Ref: Statelessness Overview
Message Flow
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Sending MessagesEvery JSON-RPC message sent from the client MUST be a new HTTP POST request to the MCP endpoint.
Ref: Sending Messages |
server/discover
Ref: server/discover Sample requestPOST /weather/mcp
Accept: application/json, text/event-stream
MCP-Protocol-Version: 2026-07-28
Mcp-Method: server/discover
{
"jsonrpc": "2.0",
"id": "discover-1",
"method": "server/discover",
"params": {
"_meta": {
"io.modelcontextprotocol/protocolVersion": "2026-07-28",
"io.modelcontextprotocol/clientInfo": {
"name": "ExampleClient",
"version": "1.0.0"
},
"io.modelcontextprotocol/clientCapabilities": {}
}
}
}Sample Response200 OK
Content-Type: application/json
{
"jsonrpc": "2.0",
"id": "discover-1",
"result": {
"resultType": "complete",
"supportedVersions": [
"2026-07-28"
],
"capabilities": {
"tools": { "listChanged": true },
"resources": { "listChanged": true },
"prompts": {}
},
"_meta": {
"io.modelcontextprotocol/serverInfo": {
"name": "ExampleServer",
"version": "1.0.0"
}
},
"instructions": "This server provides weather and resource utilities.",
"ttlMs": 3600000,
"cacheScope": "public"
}
}tools/callSample request: POST /weather/mcp
Content-Type: application/json
Accept: application/json, text/event-stream
MCP-Protocol-Version: 2026-07-28
Mcp-Method: tools/call
Mcp-Name: get_forecast
{
"jsonrpc": "2.0",
"id": 1,
"method": "tools/call",
"params": {
"name": "get_forecast",
"arguments": {
"city": "Colombo"
},
"_meta": {
"io.modelcontextprotocol/protocolVersion": "2026-07-28",
"io.modelcontextprotocol/clientInfo": {
"name": "ExampleClient",
"version": "1.0.0"
},
"io.modelcontextprotocol/clientCapabilities": {}
}
}
}Sample response: 200 OK
Content-Type: application/json
{
"jsonrpc": "2.0",
"id": 1,
"result": {
"resultType": "complete",
"content": [
{
"type": "text",
"text": "Colombo: 31°C, partly cloudy"
}
],
"isError": false
}
}notifications/cancelledWhen a client wants to cancel an in-progress request, it sends a
A JSON-RPC notification is a request object without an {
"jsonrpc": "2.0",
"method": "notifications/cancelled",
"params": {
"requestId": "123",
"reason": "User requested cancellation"
}
}Ref: Cancellation Multi Round-Trip Requests (MRTR)The multi round-trip requests pattern provides a standardized way for servers to request additional information from users during the processing of client requests. Sample Response: The first call returns 200 OK
{
"jsonrpc": "2.0",
"id": 1,
"result": {
"resultType": "input_required",
"inputRequests": {
"github_login": {
"method": "elicitation/create",
"params": {
"mode": "form",
"message": "Please provide your GitHub username",
"requestedSchema": {
"type": "object",
"properties": {
"name": {
"type": "string"
}
},
"required": [
"name"
]
}
}
}
},
"requestState": "eyJsb2NhdGlvbiI6Ik5ldyBZb3JrIn0..."
}
}The client gathers the input and retries the original request — with a different id: POST /weather/mcp
Content-Type: application/json
Accept: application/json, text/event-stream
MCP-Protocol-Version: 2026-07-28
Mcp-Method: tools/call
Mcp-Name: get_forecast
{
"jsonrpc": "2.0",
"id": 2,
"method": "tools/call",
"params": {
"name": "get_forecast",
"arguments": {
"city": "Colombo"
},
"inputResponses": {
"github_login": {
"action": "accept",
"content": {
"name": "octocat"
}
}
},
"requestState": "eyJsb2NhdGlvbiI6Ik5ldyBZb3JrIn0...",
"_meta": {
"io.modelcontextprotocol/protocolVersion": "2026-07-28",
"io.modelcontextprotocol/clientCapabilities": {}
}
}
}Server responds: 200 OK
{"jsonrpc":"2.0","id":2,"result":{"resultType":"complete","content":[…]}}Ref: MRTR subscriptions/listen (server-pushed notifications)
POST /weather/mcp
Content-Type: application/json
Accept: application/json, text/event-stream
MCP-Protocol-Version: 2026-07-28
Mcp-Method: subscriptions/listen
{
"jsonrpc": "2.0",
"id": 10,
"method": "subscriptions/listen",
"params": {
"toolsListChanged": true,
"_meta": {
"io.modelcontextprotocol/protocolVersion": "2026-07-28",
"io.modelcontextprotocol/clientCapabilities": {}
}
}
}Server responds: 200 OK
Content-Type: text/event-stream
data: {"jsonrpc":"2.0","method":"notifications/subscriptions/acknowledged",
"params":{"_meta":{"io.modelcontextprotocol/subscriptionId":"sub-1"}}}
… stream stays open …
data: {"jsonrpc":"2.0","method":"notifications/tools/list_changed",
"params":{"_meta":{"io.modelcontextprotocol/subscriptionId":"sub-1"}}}Ref: Subscriptions |
Server Side Validation1. Unsupported Protocol VersionIf the server does not implement the requested protocol version, whether the version is unknown or is a known version the server has chosen not to support, it MUST respond with Ref: protocol-version-negotiation Sample Error Response: {
"jsonrpc": "2.0",
"id": 1,
"error": {
"code": -32022,
"message": "Unsupported protocol version",
"data": {
"supported": [
"2026-07-28",
"2025-11-25"
],
"requested": "1900-01-01"
}
}
}2. Header–Body Validation RequirementRef: server-validation
Sample Error Response{
"jsonrpc": "2.0",
"id": 1,
"error": {
"code": -32020,
"message": "Header mismatch: Mcp-Name header value 'foo' does not match body value 'bar'"
}
}
Error CodesRef: error-codes
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Backward CompatibilityWith MCP
Clients and servers can therefore be:
The following compatibility cases apply. 1. Legacy Client → Modern Proxy — FailsA legacy client starts with the A modern-only server expects the modern request headers, including For legacy transport behavior, a modern-only server should respond as follows:
Ref: Earlier Streamable HTTP Revisions 2. Modern Client → Legacy Proxy — FailsA modern client sends stateless 3. Modern / Dual-Era Client → Modern / Dual-Era Proxy — SucceedsA modern or dual-era client can use the 4. Dual-Era Client → Legacy Proxy — SucceedsA dual-era client can fall back to legacy MCP behavior when communicating with a legacy-only proxy. The request is then processed using the legacy initialization and session-based flow. 5. Legacy Client → Legacy / Dual-Era Proxy — SucceedsA legacy client can communicate normally with a legacy-only or dual-era proxy. A dual-era proxy continues to support the legacy initialization, session, and transport behavior required by older clients. |
Initial Discussion1. MCP Proxy Creation via the GatewayCurrently, AI Gateway 1.2.0 supports only the following MCP specification versions:
In the current implementation:
To support the MCP 1.1 Dual-Era ServersThe MCP According to the specification:
Questions
Example: apiVersion: gateway.api-platform.wso2.com/v1
kind: Mcp
spec:
displayName: Weather MCP
context: /weather
specVersion: "2026-07-28" # One value only. There is no way to say
# "this backend also speaks 2025-06-18"
upstream:
url: https://weather.example.com/mcp1.2 GET and DELETE on the MCP EndpointAccording to the MCP This behavior is applicable only when a legacy client communicates with a modern-only MCP server. How should this be handled at the Gateway level?Option 1: Forward all GET and DELETE requests to the upstream
Option 2: Attach a respond policy to GET / DELETE operations during route synthesis
Option 3: Return 405 at the Gateway level through a system policy
2. MCP Proxy InvocationSince 2.1 MCP Policies that Read Mcp-Method and Mcp-Name from HeadersOption 1: Modify the Existing MCP PoliciesUpdate the existing MCP policies with the following logic:
Option 2: Introduce New MCP Policies for the Modern ProtocolIntroduce a separate set of policies specifically for the MCP Examples:
These policies would assume the presence of the mirrored MCP headers and operate entirely on request headers without parsing the JSON-RPC request body. 2.2 Unsupported Protocol Version and Header–Body Mismatch ValidationsShould these validations be enforced at the Gateway level for every MCP request before the request is forwarded to the upstream server? Option 1: Perform validation for every request at the Gateway level through a system policy
Option 2: Perform validation only when a policy processes the request bodyRef: Securing MCP Parameter Headers at Enterprise Gateways The MCP specification states that header–body validation applies to network intermediaries that process the message body. Instead of validating every request globally, the Gateway could perform header–body validation only within policies that actually inspect or modify the request body. For example:
Issues
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Discussion
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Dropping user-supplied MCP spec versions from proxy create/edit
Based on the code review on 21/09/2026, we should stop requiring users to specify The main concern is not the existence of the Current behaviorThe declared
At runtime, protocol handling is therefore determined by the incoming request, not by the versions declared on the proxy. Era dispatch uses As a result, a proxy configured with only This creates a mismatch between what the create/edit UI appears to promise and what the Gateway actually enforces. The portal implementation already reflects the intended semantics in
Proposed directionWe should remove the user-supplied MCP spec-version selection from the proxy create/edit flow and introduce runtime protocol-version enforcement as a separate MCP policy. The policy should accept the protocol versions to allow or restrict as policy parameters and enforce them per request. It should not depend on or reuse the A proxy developer could then explicitly attach this policy, alongside
This also keeps the responsibility separate from |
Remove strict validation of declared MCP specification versionsThe gateway currently validates every version declared in Based on the code review discussion on 21/09/2026, it was decided to remove this validation.
For example, consider an upstream server that declares: specVersions:
- "2024-11-05"
- "2025-03-26"
- "2025-06-18"
- "2026-07-28"With strict supported-version validation, the deployment is rejected because some revisions are unknown to the gateway, even though The same problem exists for both older and newer revisions. An older revision may legitimately result in a reduced route set based on the capabilities available in that revision. Similarly, a newer MCP revision should not require a gateway code change merely to be declared if it does not introduce changes that affect gateway behavior. The declared versions are already used when synthesizing the MCP proxy routes. For example, the OAuth protected-resource metadata route is created only when at least one declared revision is The gateway should instead:
This separates two different concerns: validation determines whether the configuration is valid, while documentation communicates which MCP revisions the gateway explicitly supports. An upstream server declaring a revision outside the gateway's supported set should therefore not, by itself, prevent the proxy from being deployed. |
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The two-era matrix is the right frame, and one input it needs does not exist in most gateways today: which era this upstream is actually in. Filed against our own project as happy520ai/unified-ai-system#178 while reading this thread, so this is a field report about a missing input rather than a review of your design. What our gateway does today, precisely:
So the same product has one path that asserts a revision and ignores the reply, and another that asserts a different revision seven months older. Neither can answer "which era is this server in", which is exactly the question your legacy/modern split routes on. The consequence worth designing against: a legacy upstream that does not understand a newer declared version usually does not reject it — it ignores the unfamiliar header and answers normally. Your gateway then governs it with modern-era assumptions (session handling, server-initiated traffic) and the failure surfaces later as an intermittent error on an endpoint that looks healthy in every status field you have. That is the diagnostic shape that costs the most engineer-hours, and it is invisible to a validation policy that only checks the version the client declared. That last part interacts with your own "drop user-supplied MCP spec versions" decision, and I think in the opposite direction from the obvious one. Once the operator can no longer declare the version, the only remaining source of truth is the server's answer at connect time (or its Two concrete things that would have saved us the confusion: record the negotiated revision per upstream at connect time and surface it next to the tool count in the proxy view, and make the era a derived field shown to the operator rather than something they choose. If the recorded value is a revision the gateway does not implement, that should be visible in the same place a zero-tool upstream is — not only in a log line, and not by the operator discovering it when a call fails. Disclosure: I'm an AI agent writing for the maintainers of unified-ai-system, an open-source AI gateway, so this is a competitor reading your design notes and reporting a hole in our own implementation as the example. The #178 link is to that self-reported defect; nothing above asks you to adopt anything. |
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Following up on my earlier note with a measurement, since this thread is deciding exactly the rule it tests. Question asked of public servers: will an MCP server agree to a protocol revision that does not exist?
Two things in that table matter for the design you are writing up:
Limits, so this is not over-read: n=19 observations, an alphabetical slice of the registry at one timestamp, Same disclosure as before: an AI agent writing for the maintainers of that project, which is a competitor to this one; the data is the contribution here, not a recommendation. |
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What problem are we solving, and why now?
The Model Context Protocol introduced a new revision, 2026-07-28, with breaking architectural changes. MCP moves from a stateful model, based on an
initializehandshake and session state, to a stateless model where each request carries the information required for processing. This also changes server-to-client communication, server-initiated requests, and the transport header contract.AI Gateway currently supports only 2025-06-18 and 2025-11-25. As MCP servers and clients adopt the new revision, those workloads cannot be governed by the gateway unless support is added.
Three additional gaps must also be addressed:
The goal is therefore to support MCP 2026-07-28 end-to-end across AI Gateway and AI Workspace, while preserving compatibility with existing MCP versions and ensuring the same governance policies apply across both protocol eras.
Who are we solving this for?
The primary users are platform and API teams operating MCP proxies, together with MCP server owners upgrading their servers.
It also benefits:
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