Key Changes changedspecification/2026-07-28/changelog
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11# Key Changes
22
33This document lists changes made to the Model Context Protocol (MCP) specification since
4the previous revision, [2025-11-25](/specification/2025-11-25).
4the previous revision, [2025-11-25](/specification/2025-11-25.md).
55
66## Major changes
77
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1919
20207. Multi Round-Trip Requests (MRTR) pattern introduced which replaces the previous approach of sending server-initiated requests, such as `roots/list`, `sampling/createMessage`, or `elicitation/create`. Servers return an `InputRequiredResult` (`resultType: "input_required"`) whose `inputRequests` field carries the requests for the additional information needed to process the request. Clients respond with `inputResponses` on a retry of the original request providing the requested information. ([SEP-2322](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2322)).
2121
228. All results now carry a required `resultType` field: `"complete"` for ordinary results and `"input_required"` for [multi round-trip request](/specification/2026-07-28/basic/patterns/mrtr) interim results. Clients **MUST** treat results from earlier-protocol servers that omit the field as `"complete"` ([SEP-2322](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2322)).
228. All results now carry a required `resultType` field: `"complete"` for ordinary results and `"input_required"` for [multi round-trip request](/specification/2026-07-28/basic/patterns/mrtr.md) interim results. Clients **MUST** treat results from earlier-protocol servers that omit the field as `"complete"` ([SEP-2322](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2322)).
2323
24249. Remove SSE stream resumability and message redelivery (the `Last-Event-ID` header and SSE event IDs) from the Streamable HTTP transport. A broken response stream loses the in-flight request; clients **MUST** re-issue it as a new request with a new request ID ([SEP-2575](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2575)).
2525
2626## Minor changes
2727
281. Add `extensions` field to `ClientCapabilities` and `ServerCapabilities` to support optional [extensions](/docs/extensions/overview) beyond the core protocol.
281. Add `extensions` field to `ClientCapabilities` and `ServerCapabilities` to support optional [extensions](/docs/extensions/overview.md) beyond the core protocol.
29292. Document OpenTelemetry trace context propagation conventions for `_meta` keys (`traceparent`, `tracestate`, `baggage`) ([SEP-414](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/414)).
30303. Servers **SHOULD** return tools from `tools/list` in a deterministic order to enable client-side caching and improve LLM prompt cache hit rates.
31314. Require standard MCP request headers (`Mcp-Method`, `Mcp-Name`) on Streamable HTTP POST requests, and add support for custom headers from tool parameters via `x-mcp-header` ([SEP-2243](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2243)).
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494911. Remove the `notifications/elicitation/complete` notification and the
5050 `elicitationId` field of URL mode elicitation requests, both introduced in
5151 `2025-11-25`. Under the
52 [Multi Round-Trip Requests](/specification/2026-07-28/basic/patterns/mrtr) pattern, the
52 [Multi Round-Trip Requests](/specification/2026-07-28/basic/patterns/mrtr.md) pattern, the
5353 client learns the outcome of an out-of-band interaction by retrying the original
5454 request, so a server-initiated completion signal — and the identifier used to
5555 correlate it — no longer fit the protocol. Servers needing to correlate an
5656 elicitation across retries encode their own identifier in `requestState`.
5712. Define an [error code allocation policy](/specification/2026-07-28/basic/index#error-codes)
5712. Define an [error code allocation policy](/specification/2026-07-28/basic/index.md#error-codes)
5858 partitioning the JSON-RPC server-error range: `-32000` to `-32019` remains
5959 implementation-defined (existing SDK usage is grandfathered), `-32020` to `-32099` is
6060 reserved for the MCP specification. Renumber the error codes introduced in this draft
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6464
6565## Deprecated
6666
67Features listed here remain part of the specification but are scheduled for removal under the [feature lifecycle and deprecation policy](/community/feature-lifecycle). New implementations should not adopt them. The [deprecated features registry](/specification/2026-07-28/deprecated) tracks every feature currently in the Deprecated state.
67Features listed here remain part of the specification but are scheduled for removal under the [feature lifecycle and deprecation policy](/community/feature-lifecycle.md). New implementations should not adopt them. The [deprecated features registry](/specification/2026-07-28/deprecated.md) tracks every feature currently in the Deprecated state.
6868
69691. Deprecate the Roots, Sampling, and Logging features
7070 ([SEP-2577](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2577)).
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78782. Reclassify the HTTP+SSE transport (deprecated since protocol version
7979 `2025-03-26`) as Deprecated under the feature lifecycle policy
8080 ([SEP-2596](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2596)).
81 Migrate to [Streamable HTTP](/specification/2026-07-28/basic/transports/streamable-http).
81 Migrate to [Streamable HTTP](/specification/2026-07-28/basic/transports/streamable-http.md).
8282
83833. Reclassify the `includeContext` values `"thisServer"` and `"allServers"`
8484 (soft-deprecated since protocol version `2025-11-25`) as Deprecated
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89894. Deprecate the OAuth 2.0 Dynamic Client Registration Protocol
9090 ([RFC7591](https://datatracker.ietf.org/doc/html/rfc7591)) as a client registration
9191 mechanism in favor of
92 [Client ID Metadata Documents](/specification/2026-07-28/basic/authorization/client-registration#client-id-metadata-documents)
92 [Client ID Metadata Documents](/specification/2026-07-28/basic/authorization/client-registration.md#client-id-metadata-documents)
9393 ([PR #2858](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2858)).
9494 It remains available for backwards compatibility with authorization servers that do
9595 not support Client ID Metadata Documents.
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101101## Governance and process updates
102102
1031031. Adopt a specification
104 [feature lifecycle and deprecation policy](/community/feature-lifecycle)
104 [feature lifecycle and deprecation policy](/community/feature-lifecycle.md)
105105 defining the Active, Deprecated, and Removed feature states, a minimum
106106 twelve-month deprecation window, and a
107 [registry of deprecated features](/specification/2026-07-28/deprecated)
107 [registry of deprecated features](/specification/2026-07-28/deprecated.md)
108108 ([SEP-2596](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2596)).
109109
110110## Process changes
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