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Bump ModelContextProtocol from 1.3.0 to 2.4.0 - #14
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--- updated-dependencies: - dependency-name: ModelContextProtocol dependency-version: 2.4.0 dependency-type: direct:production update-type: version-update:semver-major ... Signed-off-by: dependabot[bot] <support@github.com>
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Updated ModelContextProtocol from 1.3.0 to 2.4.0.
Release notes
Sourced from ModelContextProtocol's releases.
2.4.0
Version 2.4.0 adds experimental MCP Skills support through the new ModelContextProtocol.Extensions.Skills package, alongside OAuth hardening and reliability improvements for transport, session, and discovery flows. MCP Apps also now match protocol property names case-sensitively.
What's Changed
Documentation Updates
Test Improvements
Repository Infrastructure Updates
Acknowledgements
... (truncated)
2.3.1
This patch release includes a security fix for authenticated stateful sessions.
What's Changed
bfbd893) by @halter73 (co-authored by @Copilot @jeffhandley @tarekgh)Repository Infrastructure Updates
Full Changelog: modelcontextprotocol/csharp-sdk@v2.3.0...v2.3.1
2.3.0
This release improves HTTP discovery, OAuth, protocol interoperability, and shutdown reliability, preserves registration order for server primitives, and exposes a
TimeProviderfor deterministic client timeout tests. It also corrects optional server-identity handling; applications readingMcpClient.ServerInfoshould adopt nullable handling.Breaking Changes
Refer to the C# SDK Versioning documentation for details on versioning and breaking change policies.
McpClient.ServerInfois nullable — #1903ImplementationtoImplementation?. Existing non-nullable assignments or dereferences can produce nullable warnings and fail warnings-as-errors builds.2026-07-28connections,ServerInfoisnullwhen the server omits optional identity metadata fromserver/discover. Legacyinitializestill requiresserverInfo. Reading the property before connecting still throwsInvalidOperationException.client.ServerInfo?.Name ?? "Unknown server". Self-reported identity must not be used for security decisions.What's Changed
ServerInfonullable #1903 by @Coding-ProfessionalDiscoverProbeTimeout, exposeMcpClientOptions.TimeProviderfor deterministic timeout tests, and default SSE to legacy initialization #1719 by @halter73 (co-authored by @Copilot)InitializationTimeoutand caller cancellation; it is excluded only from the short discovery-probe budget.HttpTransportMode.SseandProtocolVersion = "2026-07-28"; pinning the version withAutoDetectis not equivalent.RequestOptionsserialization #1832 by @dfedoryshchevDocumentation Updates
Test Improvements
Repository Infrastructure Updates
McpServerFactoryreferences in Copilot instructions #1892 by @Zir0-93Acknowledgements
... (truncated)
2.2.0
This release adds hybrid stateful/stateless HTTP serving so clients using the 2025-11-25 and 2026-07-28 protocol revisions can share an endpoint, and fixes a malformed header-decoding edge case.
What's Changed
Test Improvements
Repository Infrastructure Updates
Acknowledgements
Full Changelog: modelcontextprotocol/csharp-sdk@v2.1.0...v2.2.0
2.1.0
This release adds an opt-in
subscriptions/listenhandler for custom server-side notification streams, improves HTTP transport fallback reliability, and expands guidance and samples for telemetry and binary resources.What's Changed
Documentation Updates
Test Improvements
Repository Infrastructure Updates
> [!NOTE]alert example #1771 by @PranavSenthilnathan (co-authored by @Copilot)Acknowledgements
Full Changelog: modelcontextprotocol/csharp-sdk@v2.0.0...v2.1.0
2.0.0
Version 2.0.0 brings the C# SDK into stable alignment with the MCP 2026-07-28 specification.
This major release introduces discovery-first negotiation, multi-round-trip requests, stateless-by-default HTTP, caching hints, standardized headers, stronger OAuth and token-cache safety, and dedicated MCP Apps and Tasks extension packages, with down-level interoperability for peers negotiating 2025-11-25 and earlier. Review the migration guidance below.
Breaking Changes
Refer to the C# SDK Versioning documentation for details on versioning and breaking-change policies.
HttpServerTransportOptions.Statelessnow defaults totrue. Stateless servers do not create transport sessions, expose the standalone SSEGET/DELETEendpoints, or support unsolicited server-to-client requests.Stateless = falsewhen an existing server requires legacy stateful behavior. Stateful-only options now produceMCP9006warnings and apply only to down-level initialize-handshake connections.server/discoverfirst and automatically fall back to the legacyinitializehandshake for down-level servers.MCP9005warnings because these features are deprecated by the 2026-07-28 specification.MCP9005temporarily if continued use is required while planning migration.ModelContextProtocol.Extensions.Tasks#1693ModelContextProtocol.Extensions.Tasks, import its namespace, register Tasks withWithTasks(...), and replace CoreRequestMethods.Tasks*constants withTasksProtocolmembers.AuthorizationRedirectDelegateandClientOAuthOptions.AuthorizationRedirectDelegatenow produceMCP9007warnings. Migrate toClientOAuthOptions.AuthorizationCallbackHandlerso callbacks can return the authorization code, state, and issuer.UseStructuredContent = trueand a non-object return type now emit the raw value and matching schema, such asstructuredContent: 72, instead of wrapping it as{ "result": 72 }.resultproperty.Tool.inputSchemaduring deserialization #1600Toolpayload withoutinputSchemanow throwsJsonExceptioninstead of silently defaulting the schema.inputSchema; an empty{}is sufficient.S256incode_challenge_methods_supported.application_typeduring dynamic client registration #1613application_type.DynamicClientRegistrationOptions.ApplicationTypeexplicitly when the inferred value is not appropriate.HttpRequestException,TimeoutException, or genuine I/O exception instead of always wrapping failures inIOException.IOException("Failed to connect transport.")wrapper. In AutoDetect mode, inspect the outerHttpRequestExceptionand its inner SSE failure.insufficient_scopechallenge that introduces no new scopes now throwsMcpExceptioninstead of retrying indefinitely.What's Changed
InheritEnvironmentVariablestoStdioClientTransportOptions#1563 by @halter73offline_accessto authorization scope when advertised (SEP-2207) #1479 by @stephentoub (co-authored by @Copilot)McpErrorCode.ResourceNotFoundper SEP-2164 #1558 by @jayaraman-venkatesanMcpClienttool cache #1590 by @tarekghScopeSelectorDelegateto OAuth options #1596 by @halllo... (truncated)
2.0.0-rc.2
This second 2.0 release candidate advances the SDK’s
2026-07-28protocol support, expands Tasks extension conformance tests, strengthens OAuth and transport behavior, and expands 2.0 guidance ahead of general availability.Thank you to the community for using the preview and release-candidate builds and for sharing feedback and issue reports that shape this release!
Breaking Changes
Refer to the C# SDK Versioning documentation for details on versioning and breaking-change policies.
DiscoverResult.ServerInfois removed; read and deserializeMeta[MetaKeys.ServerInfo]instead.2026-07-28, replace legacy initialization, ping, logging, and resource-subscription methods withserver/discover,_metalog level, andsubscriptions/listen.statethroughAuthorizationResult.State, and should returnCode,State, andIss.IOExceptionwrapper.What's Changed
Documentation Updates
Test Improvements
_meta.uiserialization round-trip tests #1698 by @yayayouyouRepository Infrastructure Updates
... (truncated)
2.0.0-rc.1
2.0.0-rc.1 advances the v2 SDK toward general availability with stronger OAuth conformance, improved dynamic client registration, and expanded Tasks validation.
We remain on-track to release 2.0.0 stable on or before 2026-07-28.
We want to give a big thanks to @KubaZ2 for reporting the critical, ship-stopping Tasks/HTTP defect in #1720, fixed by #1722!
Breaking Changes
Refer to the C# SDK Versioning documentation for details on versioning and breaking change policies.
Remove the preview task-scope helper #1722
McpTasksServerExtensions.CreateMcpTaskScope(...)was removed from the stable surface. This affects only applications built against the v2 preview API; no stable 2.0 release has shipped.Harden OAuth issuer validation #1605
AuthorizationRedirectDelegatenow producesMCP9007, which breaks warning-as-error builds; the manual authorization flow now requires the complete redirect URL.AuthorizationCallbackHandlerand returnAuthorizationResult.Require advertised PKCE S256 support #1700
code_challenge_methods_supported: ["S256"]now cause authentication to fail instead of receiving an inferred default.Send Dynamic Client Registration application types #1613
ApplicationTypenow sends an inferredapplication_typeinstead of omitting it.DynamicClientRegistrationOptions.ApplicationTypeexplicitly when the authorization server requires another value.What's Changed
application_typein Dynamic Client Registration requests #1613 by @jayaraman-venkatesan (co-authored by @Copilot)ClientOAuthProvider#1605 by @mikekistler (co-authored by @halter73 @Copilot)Documentation Updates
release/1.x(v1.4.1) andmain(v2 preview) content #1727 by @jeffhandley (co-authored by @Copilot)Test Improvements
... (truncated)
2.0.0-preview.3
This preview reorganizes the Tasks feature into its own
ModelContextProtocol.Extensions.Taskspackage, keepingModelContextProtocol.Corefocused on the base protocol while a new generic request-handler and alternate-result surface lets the Tasks package layer on top. It also delivers correctness fixes to the draft2026-07-28protocol -- per-request client capabilities, negotiation boundaries, and theresultTypediscriminator -- plus Streamable HTTP client improvements (an empty-JSON-response fix and a new standalone GET-stream opt-out) and conformance-test consolidation.Breaking Changes
Refer to the C# SDK Versioning documentation for details on versioning and breaking change policies.
ModelContextProtocol.Extensions.Taskspackage #1693McpTaskStatus,IMcpTaskStore/InMemoryMcpTaskStore, thetasks/*request methods, and the clientGetTaskAsync/UpdateTaskAsync/CancelTaskAsync/CallToolRawAsyncmethods -- is removed fromModelContextProtocol.Coreand relocated to the newModelContextProtocol.Extensions.Taskspackage under theModelContextProtocol.Extensions.Tasksnamespace.ResultOrAlternate<T>(replacingResultOrCreatedTask<T>) plus generic extension points --McpServerRequestHandler,McpServerOptions.RequestHandlers,McpServerHandlers.CallToolWithAlternateHandler,McpRequestFilters.CallToolWithAlternateFilters, andMcpServer.InterceptOutgoingRequests-- that the Tasks package builds on.PackageReferencetoModelContextProtocol.Extensions.Tasks; changeusing ModelContextProtocol.Protocol;tousing ModelContextProtocol.Extensions.Tasks;for task types; the task client/server APIs are now extension methods (McpTasksClientExtensions/McpTasksServerExtensions), and the task store is registered via the new builder extensions instead ofMcpServerOptions.TaskStore.Experimental APIs
To support extracting Tasks (#1693),
ModelContextProtocol.Coregained a generic server-extension surface --ResultOrAlternate<T>,McpServerRequestHandler,McpServerOptions.RequestHandlers,McpServerHandlers.CallToolWithAlternateHandler,McpRequestFilters.CallToolWithAlternateFilters, andMcpServer.InterceptOutgoingRequests-- that lets extension packages such asModelContextProtocol.Extensions.Taskslayer behavior onto the server pipeline. These APIs are annotated[Experimental]under diagnostic IDMCPEXP002.This surface is still being designed: #1704 tracks composing these seams with the normal filter and subscription pipeline (typed custom RPCs, filter composition, and extension-defined subscriptions). Expect these low-level extensibility APIs to change and potentially remain
[Experimental]through the 2.0.0 stable release.What's Changed
ModelContextProtocol.Extensions.Tasksextension package #1693 by @jeffhandley (co-authored by @Copilot)Test Improvements
Acknowledgements
Full Changelog: modelcontextprotocol/csharp-sdk@v2.0.0-preview.2...v2.0.0-preview.3
2.0.0-preview.2
This second preview of the 2.0.0 series advances the SDK's alignment with the upcoming
2026-07-28MCP protocol revision: it adds client-side conformance diagnostics for the SEP-2549 caching hints, makes Streamable HTTP error responses echo the request id per the base protocol and SEP-2243, and fully stabilizes now-stable protocol properties so consumer-defined source generators serialize them correctly. Separately -- and unrelated to the protocol revision -- it introducesDeferChangedEvents()onMcpServerPrimitiveCollection<T>for batchinglist_changednotifications when registering primitives in bulk. There are no breaking changes relative tov2.0.0-preview.1.What's Changed
Documentation Updates
Acknowledgements
Full Changelog: modelcontextprotocol/csharp-sdk@v2.0.0-preview.1...v2.0.0-preview.2
2.0.0-preview.1
This is the first preview of the C# MCP SDK 2.0.0, designed for alignment with the 2026-07-28 MCP specification release. The SDK implements the
2026-07-28protocol version which fundamentally changes how clients and servers interact -- removing theinitializehandshake (SEP-2575), eliminating server-side session state (SEP-2567), introducing Multi Round-Trip Requests (SEP-2322), and deprecating legacy capabilities in favor of the new extensions framework (SEP-2133).The 2.0.0 SDK is fully backward-compatible with servers and clients using the previous
2024-11-05protocol version. Clients automatically negotiate down to the legacyinitializehandshake when connecting to older servers, and servers continue to acceptinitializerequests from older clients. API breaking changes in 2.0.0 are limited to two categories: (1) APIs for capabilities deprecated by the new specification (Roots, Sampling, and Logging), which are now marked[Obsolete]with guidance toward their replacements, and (2) experimental APIs whose contracts changed as the specifications were finalized. Stable, non-deprecated APIs from 1.x continue to work without modification.Protocol Version Negotiation and Handshake Behavior
The 2.0.0 SDK introduces a fundamentally new connection lifecycle:
Default behavior (no configuration needed):
server/discoverrequest withMCP-Protocol-Version: 2026-07-282026-07-28protocol version, it responds with capabilities -- no handshake, no sessionMcpClientOptions.DiscoverProbeTimeout), the client automatically falls back to the legacyinitializehandshake with2025-11-25-32022UnsupportedProtocolVersion,-32021MissingRequiredClientCapability,-32020HeaderMismatch) are never treated as legacy indicators and are surfaced as errorsOpting out of the
2026-07-28protocol version:McpClientOptions.ProtocolVersion = "2025-11-25"to force the legacyinitializehandshake and disable the automatic fallback (a non-nullProtocolVersionnow acts as both the requested version and the minimum the client accepts)Per-request metadata (
2026-07-28protocol version):_metawithio.modelcontextprotocol/protocolVersion,io.modelcontextprotocol/clientInfo, andio.modelcontextprotocol/clientCapabilities2026-07-28 Spec Alignment: SEP Implementation Status
The 2026-07-28 specification release includes 22 SEPs. The table below summarizes C# SDK status. Remaining work is tracked in the 2026-07-28 Spec Compliance milestone.
1.4.2
This patch release includes security fixes for OAuth authentication and authenticated HTTP sessions.
What's Changed
Deployments using metadata-free 2025-03-26 OAuth discovery may explicitly enable the legacy endpoint fallback only after independently verifying PKCE enforcement; otherwise, update metadata to advertise S256. The process-wide opt-in is
ModelContextProtocol.Authentication.AllowLegacyOAuthMetadataFallback; it does not bypass validation of discovered metadata.Documentation Updates
Repository Infrastructure Updates
Acknowledgements
Full Changelog: modelcontextprotocol/csharp-sdk@v1.4.1...v1.4.2
1.4.1
This release backports a memory-leak fix for HTTP/SSE-based MCP servers.
StreamableHttpServerTransportnow releases its Server-Sent Events response stream reference as soon as a GET request ends, instead of holding it until the session is disposed via explicit DELETE or idle timeout. Long-lived SSE clients that disconnect without sending DELETE no longer pin the underlying Kestrel connection and its associated memory-pool buffers (~20 MiB per session), preventing the sustained memory growth that could accumulate under connect/disconnect churn.What's Changed
Acknowledgements
Full Changelog: modelcontextprotocol/csharp-sdk@v1.4.0...v1.4.1
1.4.0
v1.4.0 introduces support for the Identity Assertion Authorization Grant (ID-JAG) flow via the new
IdentityAssertionGrantProvider, enabling enterprise SSO scenarios where users authenticate once via their enterprise Identity Provider and access MCP servers without per-server authorization prompts. The release also adds a newInheritEnvironmentVariablesoption onStdioClientTransportOptionsfor controlling the child server's environment, alongside two security hardening fixes: the stdio client transport no longer enumerates child-process environment variables in Trace logs, andDELETEon a Streamable HTTP session now requires the same authenticated user that initiated the session.What's Changed
InheritEnvironmentVariablestoStdioClientTransportOptions#1563 by @halter73 (co-authored by @Copilot)HandleDeleteRequestAsyncnow mirrors theHasSameUserIdcheck already enforced on GET and POST. ADELETEwith a validMcp-Session-Idbut a different authenticated user now returns403 Forbiddeninstead of terminating the session — defense-in-depth against a leaked session ID being used to DoS the original owner.IdentityAssertionGrantProviderand supporting option/response types inModelContextProtocol.Authenticationimplementing the Identity Assertion Authorization Grant flow: RFC 8693 token exchange at the enterprise IdP (ID Token → JWT Authorization Grant) followed by RFC 7523 JWT bearer grant at the MCP authorization server (JAG → access token). See the new Cross-Application Access section in the transport docs for full usage details.Documentation Updates
Repository Infrastructure Updates
Acknowledgements
Full Changelog: modelcontextprotocol/csharp-sdk@v1.3.0...v1.4.0
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