v2.2.0-M1

Highlights

• Modern stateless server for MCP 2026-07-28: #1170 by @chemicL

  The first step toward the stateless Streamable HTTP paradigm. It is a new server in io.modelcontextprotocol.modern, independent of the legacy McpSchema, and it passes all 37 required 2026-07-28 conformance scenarios.

  • No sessions: each request is handled on its own, which suits horizontally scaled deployments.
  • One server, sync or async: many concepts were simplified and allow the transport to choose whether to offload blocking code or not, freeing the user to use either a synchronous or asynchronous paradigm to implement features.
  • Your own catalogs: tools, resources and prompts come from repositories you implement, so per-tenant, filtered and paginated catalogs are straightforward.
  • Stream only when it pays: handlers return plain JSON or SSE, user code decides.
  • Not yet supported: a modern client, tasks and SEP-2243 custom headers.

Dependencies

• Upgrade Reactor to 2026.0.0-M2. #1191 by @chemicL

Full Changelog: v2.1.0...v2.2.0-M1

v2.1.0

Highlights

• Tool list filtering #1108 by @Kehrlann
• HTTP client transport rework: HttpClient-based transports are now Publisher-based, and request customizers compose on the builders.
  • #1079 by @Kehrlann and @chemicL
  • #1165 by @Kehrlann

Enhancements

• extensions attribute on ClientCapabilities and ServerCapabilities (SEP-2133). #1064 by @YousefHaggy
• ServerHttpHeaderValidator replaces ServerTransportSecurityValidator. #982 by @neerajbhatt
• Streamable HTTP server session sweeping and keep-alive. #1130 by @Kehrlann
• Remove the 2024-11-05 protocol from Streamable HTTP. #1126 by @Kehrlann
• Reject non-application/json POST requests. #1164 by @Kehrlann

Bug fixes

• Stream leak when resuming with LAST_EVENT_ID. #1127 by @Kehrlann
• STDIO sendMessage is now thread-safe. #935 by @nquinquenel
• Malformed request bodies return 400 INVALID_REQUEST with Jackson 3. #1168 by @Kehrlann
• listXyz() methods return re-subscribable Monos. #1175 by @kamisheng
• NPE when changing features on a server with derived capabilities. #1178 by @itzjb
• NPE in addRoot/removeRoot when roots listChanged is unset. #1179 by @Kehrlann
• Automatic-Module-Name no longer contains hyphens. #1135 by @Kehrlann
• Log instead of aggregating exceptions in JSONRPCErrorResponse. #1182 by @Kehrlann

New contributors

@slachiewicz, @YousefHaggy, @kamisheng, @itzjb, @neerajbhatt and @nquinquenel

Full Changelog: v2.0.1...v2.1.0

v1.1.5

What's Changed

• Fix error behavior on unregistered handlers in stateless server handler by @Kehrlann in #1109
• Remove aggregate exception from JSONRPCErrorResponse, log instead by @Kehrlann in #1183
• Streamable HTTP: Add session sweeping and close hanging streams by @Kehrlann in #1185

Full Changelog: v1.1.4...v1.1.5

v0.18.5

What's Changed

• Fix error behavior on unregistered handlers in stateless server handler by @olsavmic in #1104
• Reject non application/json POST requests by @Kehrlann in #1169
• Remove aggregate exception from JSONRPCErrorResponse, log instead by @Kehrlann in #1184
• Introduce session sweeping by @Kehrlann in #1187

New Contributors

• @olsavmic made their first contribution in #1104

Full Changelog: v0.18.4...v0.18.5

v2.0.1

What's Changed

• Upgrade conformance suite to 0.1.16, Spring AI conformance to 2.0.0 GA by @Kehrlann in #1032
• Return empty completion when no handler matches a valid ref by @jstar0 in #996
• Close response after sending error in McpStreamableServerSession#responseStream by @Kehrlann in #1041
• Fix error behavior on unregistered handlers in stateless server handler by @maff in #800
• Remove invalid WARN message for missing notification handler in stateless servers by @bperhaps in #835
• Fix SSE event classification to follow spec for missing event field by @iaJingda in #913
• fix: stop pagination on empty cursors by @nanookclaw in #954
• fix McpTransportContext.create() mutability issue and add tests by @iuliiasobolevska in #1076
• Bound HTTP server and client reads by @Kehrlann in #1102
• Bound STDIO server and client reads by @Kehrlann in #1103

Depedency updates

• Bump json-schema-validator to 2.0.4 / 3.0.6, jackson to 2.21.1 / 3.1.4 by @joaodinissf in #1058

New Contributors

• @jstar0 made their first contribution in #996
• @ammbra made their first contribution in #1044
• @maff made their first contribution in #800
• @bperhaps made their first contribution in #835
• @iaJingda made their first contribution in #913
• @nanookclaw made their first contribution in #954
• @iuliiasobolevska made their first contribution in #1076

Full Changelog: v2.0.0...v2.0.1

v1.1.4

What's changed

• Bound HTTP client and server reads (backported from #1102 by @Kehrlann)

Full Changelog: v1.1.3...v1.1.4

v0.18.4

What's changed

• Bound HTTP client and server reads (backported from #1102 by @Kehrlann)

Full Changelog: v0.18.3...v0.18.4

v2.0.0

MCP Java SDK 2.0.0 🎉

We're thrilled to announce the General Availability of the MCP Java SDK 2.0.0 — the first major release since 1.x and the culmination of three milestones (M1, M2, M3) and a release candidate (RC1). It tracks the latest 2025-11-25 MCP specification and lays the groundwork for everything that comes next. Huge thanks to everyone who contributed, tested the milestones, and filed feedback along the way! ❤️

Upgrading from 1.x? See the v2 migration guide and the updated documentation (#1024) for a step-by-step walkthrough of the breaking changes below.

Highlights

• A new JSON compatibility foundation for consistent forward/backward wire compatibility as the protocol evolves.
• Spec-accurate schema with enforced required fields and lenient wire deserialization.
• End-to-end validation of tool inputs and embedded JSON Schema documents (2020-12).
• Richer elicitation: client-side schema defaults, URL elicitation, and form-based elicitation schemas.
• Icons & metadata support (SEP-973) across the API.
• Streamable HTTP first: SSE transports are now deprecated in favor of Streamable HTTP.
• Cleaner, quieter logging with unified configuration and saner default levels.

⚠️ Breaking Changes

• feat!: consistent JSON forward/backward compatibility — the 2.0 foundation by @chemicL in #927
• feat!: enforce required MCP spec fields in McpSchema; lenient wire deserialization by @chemicL in #928
• feat!: add tool input arguments validation (#697) by @ashakirin in #873
• fix: Remove JsonSchema and use a Map for inputSchema to support JSON Schema dialects by @bilaloumehdi in #749

✨ New Features

• feat: validate embedded JSON Schema documents against the 2020-12 meta-schema (SEP-1613) by @chemicL in #949
• feat: Add SEP-973 icons and metadata support by @sainathreddyb in #912
• feat: client-side application of elicitation schema defaults (SEP-1034) by @chemicL in #976
• Add URL elicitation support (SEP-1036) by @Kehrlann in #993
• Add schemas for form-based elicitation by @Kehrlann in #1020
• feat: add support for meta parameter in client paginated list queries by @smohite04 in #906
• Add 2025-11-25 spec version to all transports by @chemicL in #1025

🔌 Transports & Networking

• Deprecate SSE transports (in favor of Streamable HTTP) by @Kehrlann in #950
• Client transports: remove deprecated methods from builder by @Kehrlann in #899
• Server transports: remove deprecated methods from builder by @Kehrlann
• HttpClientStreamableHttpTransport: handle HTTP 405 by @Kehrlann
• Validate message endpoint in SSE client transport by @Kehrlann in #943
• DefaultSseMessageEndpointValidator allows same-origin message endpoints by @Kehrlann in #946
• Deprecate Builder.customizeRequest() in favor of httpRequestCustomizer() by @gyeo009 in #791
• Expose request URI in McpHttpClientAuthorizationErrorHandler by @Kehrlann in #980
• Fix UTF-8 encoding for non-ASCII tool names in HTTP client transports by @rameshreddy-adutla in #850

🪵 Logging

• Unify logging config by @chemicL in #984
• Reduce logging levels by @chemicL in #985

🐛 Fixes & Polish

• fix: avoid dropped errors when transport is closed or uninitialized by @chemicL in #995
• fix: Return empty prompt completion result when prompt has no arguments by @chemicL in #934
• Revert removed builders for Resource and ResourceTemplate by @chemicL in #947
• Clarify tool validation error messages by @tzolov in #1023
• Return void from McpStatelessSyncServer#closeGracefully instead of Mono by @tzolov in #1019
• fix: add missing Export-Package to mcp-json-jackson2 and mcp-json-jackson3 by @joaodinissf in #911

📚 Docs & Conformance

• Update documentation and migration notes for v2 by @chemicL in #1024
• conformance-tests: upgrade to MCP-security 0.1.11, implement CIMD by @Kehrlann in #975
• conformance: update to mcp-security 0.1.5, pass scope-step-up by @Kehrlann in #895
• docs: document best practice for handling argument errors in MCP tools by @radeshgovind-2005 in #891
• fix: proper URL links from README.md to 'Java Dependencies', 'Java MCP Client', 'Java MCP Server' pages by @sleepytomcat in #874

New Contributors

• @sleepytomcat made their first contribution in #874
• @radeshgovind-2005 made their first contribution in #891
• @gyeo009 made their first contribution in #791
• @rameshreddy-adutla made their first contribution in #850
• @smohite04 made their first contribution in #906
• @bilaloumehdi made their first contribution in #749
• @sainathreddyb made their first contribution in #912
• @joaodinissf made their first contribution in #911

Full Changelog: v1.1.0...v2.0.0

v0.18.3

What's changed

Fix for GHSA-hv2w-8mjj-jw22

Full Changelog: v0.18.2...v0.18.3

v2.0.0-RC1

What's Changed

• feat: client-side application of elicitation schema defaults (SEP-1034) by @chemicL in #976
• Expose request URI in McpHttpClientAuthorizationErrorHandler by @Kehrlann in #980
• Unify logging config by @chemicL in #984
• Reduce logging levels by @chemicL in #985
• fix: add missing Export-Package to mcp-json-jackson2 and mcp-json-jackson3 by @joaodinissf in #911
• Add URL elicitation support (SEP-1036) by @Kehrlann in #993
• fix: avoid dropped errors when transport is closed or uninitialized by @chemicL in #995

New Contributors

• @joaodinissf made their first contribution in #911

Full Changelog: v2.0.0-M3...v2.0.0-RC1