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mcp: Deprecate roots, sampling and logging (SEP-2577) (#1017)

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Fixes #1013
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Guglielmo Colombo 2026-06-23 11:11:08 +02:00 • committed by GitHub
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7
README.md
View file

@ -44,6 +44,13 @@ The following table shows which versions of the Go SDK support which versions of
\*\* Partial support for 2025-11-25 (client side OAuth and Sampling with tools not available).
The roots, sampling, and logging features are deprecated as of protocol version
2026-07-28 by
[SEP-2577](https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging).
The SDK continues to support them for compatibility during the deprecation
window (at least twelve months). See the individual feature documentation for
migration guidance.
New releases of the SDK target only supported versions of Go. See
https://go.dev/doc/devel/release#policy for more information.

2
conformance/everything-server/main.go
View file

@ -5,6 +5,8 @@
// The conformance server implements features required for MCP conformance testing.
// It mirrors the functionality of the TypeScript conformance server at
// https://github.com/modelcontextprotocol/conformance/blob/main/examples/servers/typescript/everything-server.ts
//
//lint:file-ignore SA1019 conformance server exercises deprecated SEP-2577 APIs (roots, sampling, logging).
package main
import (

14
docs/client.md
View file

@ -10,6 +10,13 @@
## Roots
> **Note:** The roots feature is deprecated as of protocol version 2026-07-28
> ([SEP-2577](https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging)).
> It remains fully functional during the deprecation window (at least twelve
> months). The SDK continues to support roots for compatibility. New code
> should pass paths via tool parameters, resource URIs, or configuration
> instead.
MCP allows clients to specify a set of filesystem
["roots"](https://modelcontextprotocol.io/specification/2025-06-18/client/roots).
The SDK supports this as follows:
@ -77,6 +84,13 @@ func Example_roots() {
## Sampling
> **Note:** The sampling feature is deprecated as of protocol version
> 2026-07-28
> ([SEP-2577](https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging)).
> It remains fully functional during the deprecation window (at least twelve
> months). The SDK continues to support sampling for compatibility. Servers
> that need LLM completions should call LLM provider APIs directly.
[Sampling](https://modelcontextprotocol.io/specification/2025-06-18/client/sampling)
is a way for servers to leverage the client's AI capabilities. It is
implemented in the SDK as follows:

7
docs/server.md
View file

@ -474,6 +474,13 @@ _ = mcp.NewServer(&mcp.Implementation{Name: "server"}, &mcp.ServerOptions{
### Logging
> **Note:** The logging feature is deprecated as of protocol version
> 2026-07-28
> ([SEP-2577](https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging)).
> It remains fully functional during the deprecation window (at least twelve
> months). The SDK continues to support logging for compatibility. Servers
> should migrate to stderr logging (for STDIO transports) or OpenTelemetry.
MCP servers can send logging messages to MCP clients.
(This form of logging is distinct from server-side logging, where the
server produces logs that remain server-side, for use by server maintainers.)

2
examples/server/distributed/main.go
View file

@ -16,6 +16,8 @@
// Example:
//
// ./distributed -http=localhost:8080 -child_ports=8081,8082
//
//lint:file-ignore SA1019 example server exercises deprecated SEP-2577 logging API for demonstration.
package main
import (

2
examples/server/everything/main.go
View file

@ -3,6 +3,8 @@
// license that can be found in the LICENSE file.
// The everything server implements all supported features of an MCP server.
//
//lint:file-ignore SA1019 example server exercises deprecated SEP-2577 APIs (roots, sampling, logging) for demonstration.
package main
import (

14
internal/docs/client.src.md
View file

@ -4,6 +4,13 @@
## Roots
> **Note:** The roots feature is deprecated as of protocol version 2026-07-28
> ([SEP-2577](https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging)).
> It remains fully functional during the deprecation window (at least twelve
> months). The SDK continues to support roots for compatibility. New code
> should pass paths via tool parameters, resource URIs, or configuration
> instead.
MCP allows clients to specify a set of filesystem
["roots"](https://modelcontextprotocol.io/specification/2025-06-18/client/roots).
The SDK supports this as follows:
@ -26,6 +33,13 @@ method. To receive notifications about root changes, set
## Sampling
> **Note:** The sampling feature is deprecated as of protocol version
> 2026-07-28
> ([SEP-2577](https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging)).
> It remains fully functional during the deprecation window (at least twelve
> months). The SDK continues to support sampling for compatibility. Servers
> that need LLM completions should call LLM provider APIs directly.
[Sampling](https://modelcontextprotocol.io/specification/2025-06-18/client/sampling)
is a way for servers to leverage the client's AI capabilities. It is
implemented in the SDK as follows:

7
internal/docs/server.src.md
View file

@ -236,6 +236,13 @@ requests.
### Logging
> **Note:** The logging feature is deprecated as of protocol version
> 2026-07-28
> ([SEP-2577](https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging)).
> It remains fully functional during the deprecation window (at least twelve
> months). The SDK continues to support logging for compatibility. Servers
> should migrate to stderr logging (for STDIO transports) or OpenTelemetry.
MCP servers can send logging messages to MCP clients.
(This form of logging is distinct from server-side logging, where the
server produces logs that remain server-side, for use by server maintainers.)

7
internal/readme/README.src.md
View file

@ -43,6 +43,13 @@ The following table shows which versions of the Go SDK support which versions of
\*\* Partial support for 2025-11-25 (client side OAuth and Sampling with tools not available).
The roots, sampling, and logging features are deprecated as of protocol version
2026-07-28 by
[SEP-2577](https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging).
The SDK continues to support them for compatibility during the deprecation
window (at least twelve months). See the individual feature documentation for
migration guidance.
New releases of the SDK target only supported versions of Go. See
https://go.dev/doc/devel/release#policy for more information.

2
mcp/capabilities_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
//lint:file-ignore SA1019 tests exercise deprecated SEP-2577 APIs (roots, sampling, logging).
package mcp
import (

47
mcp/client.go
View file

@ -82,6 +82,12 @@ type ClientOptions struct {
// &SamplingCapabilities{}. If [ClientOptions.Capabilities] is set and has a
// non nil value for [ClientCapabilities.Sampling], that value overrides the
// inferred capability.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). Migrate to calling LLM provider APIs
// directly from your server. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
CreateMessageHandler func(context.Context, *CreateMessageRequest) (*CreateMessageResult, error)
// CreateMessageWithToolsHandler handles incoming sampling/createMessage
// requests that may involve tool use. It returns
@ -95,6 +101,12 @@ type ClientOptions struct {
//
// It is a panic to set both CreateMessageHandler and
// CreateMessageWithToolsHandler.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). Migrate to calling LLM provider APIs
// directly from your server. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
CreateMessageWithToolsHandler func(context.Context, *CreateMessageWithToolsRequest) (*CreateMessageWithToolsResult, error)
// ElicitationHandler handles incoming requests for elicitation/create.
//
@ -152,10 +164,17 @@ type ClientOptions struct {
// ElicitationCompleteHandler handles incoming notifications for notifications/elicitation/complete.
ElicitationCompleteHandler func(context.Context, *ElicitationCompleteNotificationRequest)
// Handlers for notifications from the server.
ToolListChangedHandler func(context.Context, *ToolListChangedRequest)
PromptListChangedHandler func(context.Context, *PromptListChangedRequest)
ResourceListChangedHandler func(context.Context, *ResourceListChangedRequest)
ResourceUpdatedHandler func(context.Context, *ResourceUpdatedNotificationRequest)
ToolListChangedHandler func(context.Context, *ToolListChangedRequest)
PromptListChangedHandler func(context.Context, *PromptListChangedRequest)
ResourceListChangedHandler func(context.Context, *ResourceListChangedRequest)
ResourceUpdatedHandler func(context.Context, *ResourceUpdatedNotificationRequest)
// LoggingMessageHandler handles incoming notifications/message
// notifications from the server.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
LoggingMessageHandler func(context.Context, *LoggingMessageRequest)
ProgressNotificationHandler func(context.Context, *ProgressNotificationClientRequest)
// MultiRoundTrip configures the automatic MultiRoundTrip (Multi Round-Trip Requests) middleware.
@ -615,6 +634,12 @@ func (cs *ClientSession) startKeepalive(interval time.Duration) {
// AddRoots adds the given roots to the client,
// replacing any with the same URIs,
// and notifies any connected servers.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). Migrate to passing paths via tool parameters,
// resource URIs, or configuration. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (c *Client) AddRoots(roots ...*Root) {
// Only notify if something could change.
if len(roots) == 0 {
@ -627,6 +652,12 @@ func (c *Client) AddRoots(roots ...*Root) {
// RemoveRoots removes the roots with the given URIs,
// and notifies any connected servers if the list has changed.
// It is not an error to remove a nonexistent root.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). Migrate to passing paths via tool parameters,
// resource URIs, or configuration. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (c *Client) RemoveRoots(uris ...string) {
changeAndNotify(c, notificationRootsListChanged, &RootsListChangedParams{},
func() bool { return c.roots.remove(uris...) })
@ -1242,6 +1273,14 @@ func (cs *ClientSession) CallTool(ctx context.Context, params *CallToolParams) (
return handleSend[*CallToolResult](ctx, methodCallTool, newClientRequest(cs, orZero[Params](params)))
}
// SetLoggingLevel sets the minimum severity level for log messages sent by
// the server.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). Migrate to consuming stderr output (for STDIO
// servers) or OpenTelemetry. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (cs *ClientSession) SetLoggingLevel(ctx context.Context, params *SetLoggingLevelParams) error {
_, err := handleSend[*emptyResult](ctx, methodSetLevel, newClientRequest(cs, orZero[Params](params)))
return err

2
mcp/client_example_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
//lint:file-ignore SA1019 examples exercise deprecated SEP-2577 APIs (roots, sampling) for demonstration.
package mcp_test
import (

2
mcp/client_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
//lint:file-ignore SA1019 tests exercise deprecated SEP-2577 APIs (roots, sampling, logging).
package mcp
import (

10
mcp/content.go
View file

@ -189,6 +189,11 @@ func (c *EmbeddedResource) fromWire(wire *wireContent) {
// ToolUseContent represents a request from the assistant to invoke a tool.
// This content type is only valid in sampling messages.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ToolUseContent struct {
// ID is a unique identifier for this tool use, used to match with ToolResultContent.
ID string
@ -229,6 +234,11 @@ func (c *ToolUseContent) fromWire(wire *wireContent) {
// ToolResultContent represents the result of a tool invocation.
// This content type is only valid in sampling messages with role "user".
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ToolResultContent struct {
// ToolUseID references the ID from the corresponding ToolUseContent.
ToolUseID string

15
mcp/logging.go
View file

@ -69,6 +69,11 @@ func compareLevels(l1, l2 LoggingLevel) int {
}
// LoggingHandlerOptions are options for a LoggingHandler.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type LoggingHandlerOptions struct {
// The value for the "logger" field of logging notifications.
LoggerName string
@ -79,6 +84,11 @@ type LoggingHandlerOptions struct {
}
// A LoggingHandler is a [slog.Handler] for MCP.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type LoggingHandler struct {
opts LoggingHandlerOptions
ss *ServerSession
@ -101,6 +111,11 @@ func ensureLogger(l *slog.Logger) *slog.Logger {
// NewLoggingHandler creates a [LoggingHandler] that logs to the given [ServerSession] using a
// [slog.JSONHandler].
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func NewLoggingHandler(ss *ServerSession, opts *LoggingHandlerOptions) *LoggingHandler {
var buf bytes.Buffer
jsonHandler := slog.NewJSONHandler(&buf, &slog.HandlerOptions{

2
mcp/mcp_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
//lint:file-ignore SA1019 tests exercise deprecated SEP-2577 APIs (roots, sampling, logging).
package mcp
import (

2
mcp/mrtr_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by the license
// that can be found in the LICENSE file.
//lint:file-ignore SA1019 tests exercise deprecated SEP-2577 APIs (roots, sampling, logging).
package mcp
import (

146
mcp/protocol.go
View file

@ -439,6 +439,11 @@ func (x *CancelledParams) GetProgressToken() any { return getProgressToken(x) }
func (x *CancelledParams) SetProgressToken(t any) { setProgressToken(x, t) }
// RootCapabilities describes a client's support for roots.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type RootCapabilities struct {
// ListChanged reports whether the client supports notifications for
// changes to the roots list.
@ -466,14 +471,27 @@ type ClientCapabilities struct {
// Deprecated: use RootsV2. As described in #607, Roots should have been a
// pointer to a RootCapabilities value. Roots will be continue to be
// populated, but any new fields will only be added in the RootsV2 field.
//
// The roots feature itself is also deprecated by SEP-2577; see RootsV2.
Roots struct {
// ListChanged reports whether the client supports notifications for
// changes to the roots list.
ListChanged bool `json:"listChanged,omitempty"`
} `json:"roots,omitempty"`
// RootsV2 is present if the client supports roots. When capabilities are explicitly configured via [ClientOptions.Capabilities]
// RootsV2 is present if the client supports roots. When capabilities are
// explicitly configured via [ClientOptions.Capabilities].
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
RootsV2 *RootCapabilities `json:"-"`
// Sampling is present if the client supports sampling from an LLM.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
Sampling *SamplingCapabilities `json:"sampling,omitempty"`
// Elicitation is present if the client supports elicitation from the server.
Elicitation *ElicitationCapabilities `json:"elicitation,omitempty"`
@ -641,6 +659,12 @@ type CompleteResult struct {
func (*CompleteResult) isResult() {}
// CreateMessageParams holds parameters for a sampling/createMessage request.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type CreateMessageParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -648,10 +672,11 @@ type CreateMessageParams struct {
// A request to include context from one or more MCP servers (including the
// caller), to be attached to the prompt. The client may ignore this request.
//
// The default is "none". Values "thisServer" and
// "allServers" are soft-deprecated. Servers SHOULD only use these values if
// the client declares ClientCapabilities.sampling.context. These values may
// be removed in future spec releases.
// The default is "none". The values "thisServer" and "allServers" are
// deprecated as of protocol version 2025-11-25 (SEP-2596) and will be
// removed no later than the sampling feature itself (SEP-2577). Servers
// SHOULD omit this field or use "none". See
// https://modelcontextprotocol.io/seps/2596-feature-lifecycle-and-deprecation-policy.
IncludeContext string `json:"includeContext,omitempty"`
// The maximum number of tokens to sample, as requested by the server. The
// client may choose to sample fewer tokens than requested.
@ -681,6 +706,11 @@ func (x *CreateMessageParams) SetProgressToken(t any) { setProgressToken(x, t) }
// and messages that support array content (for parallel tool calls).
//
// Use with [ServerSession.CreateMessageWithTools].
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type CreateMessageWithToolsParams struct {
Meta `json:"_meta,omitempty"`
IncludeContext string `json:"includeContext,omitempty"`
@ -741,6 +771,11 @@ func (p *CreateMessageWithToolsParams) toBase() (*CreateMessageParams, error) {
// object for compatibility with pre-2025-11-25 implementations. When
// unmarshaling, a single JSON content object is accepted and wrapped in a
// one-element slice.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type SamplingMessageV2 struct {
Content []Content `json:"content"`
Role Role `json:"role"`
@ -782,6 +817,11 @@ func (m *SamplingMessageV2) UnmarshalJSON(data []byte) error {
// The client should inform the user before returning the sampled message, to
// allow them to inspect the response (human in the loop) and decide whether to
// allow the server to see it.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type CreateMessageResult struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -828,6 +868,11 @@ func (r *CreateMessageResult) UnmarshalJSON(data []byte) error {
//
// When unmarshaling, a single JSON content object is accepted and wrapped in a
// one-element slice, for compatibility with clients that return a single block.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type CreateMessageWithToolsResult struct {
Meta `json:"_meta,omitempty"`
Content []Content `json:"content"`
@ -1218,6 +1263,12 @@ type ListResourcesResult struct {
func (x *ListResourcesResult) isResult() {}
func (x *ListResourcesResult) nextCursorPtr() *string { return &x.NextCursor }
// ListRootsParams holds parameters for a roots/list request.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ListRootsParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -1233,6 +1284,11 @@ func (x *ListRootsParams) SetProgressToken(t any) { setProgressToken(x, t) }
// The client's response to a roots/list request from the server. This result
// contains an array of Root objects, each representing a root directory or file
// that the server can operate on.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ListRootsResult struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -1277,8 +1333,20 @@ func (x *ListToolsResult) nextCursorPtr() *string { return &x.NextCursor }
//
// These map to syslog message severities, as specified in RFC-5424:
// https://datatracker.ietf.org/doc/html/rfc5424#section-6.2.1
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type LoggingLevel string
// LoggingMessageParams holds the parameters for a notifications/message
// notification.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type LoggingMessageParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -1301,6 +1369,11 @@ func (x *LoggingMessageParams) SetProgressToken(t any) { setProgressToken(x, t)
//
// Keys not declared here are currently left unspecified by the spec and are up
// to the client to interpret.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ModelHint struct {
// A hint for a model name.
//
@ -1327,6 +1400,11 @@ type ModelHint struct {
// These preferences are always advisory. The client may ignore them. It is also
// up to the client to decide how to interpret these preferences and how to
// balance them against other considerations.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ModelPreferences struct {
// How much to prioritize cost when selecting a model. A value of 0 means cost
// is not important, while a value of 1 means cost is the most important factor.
@ -1652,6 +1730,11 @@ type ResourceTemplate struct {
type Role string
// Represents a root directory or file that the server can operate on.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type Root struct {
// See [specification/2025-06-18/basic/index#general-fields] for notes on _meta
// usage.
@ -1666,6 +1749,13 @@ type Root struct {
URI string `json:"uri"`
}
// RootsListChangedParams holds parameters for a notifications/roots/list_changed
// notification.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type RootsListChangedParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -1681,6 +1771,11 @@ func (x *RootsListChangedParams) SetProgressToken(t any) { setProgressToken(x, t
// below directly above ClientCapabilities.
// SamplingCapabilities describes the client's support for sampling.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type SamplingCapabilities struct {
// Context indicates the client supports includeContext values other than "none".
Context *SamplingContextCapabilities `json:"context,omitempty"`
@ -1689,12 +1784,27 @@ type SamplingCapabilities struct {
}
// SamplingContextCapabilities indicates the client supports context inclusion.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type SamplingContextCapabilities struct{}
// SamplingToolsCapabilities indicates the client supports tool use in sampling.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type SamplingToolsCapabilities struct{}
// ToolChoice controls how the model uses tools during sampling.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ToolChoice struct {
// Mode controls tool invocation behavior:
// - "auto": Model decides whether to use tools (default)
@ -1721,6 +1831,11 @@ type URLElicitationCapabilities struct{}
//
// For assistant messages, Content may be text, image, audio, or tool_use.
// For user messages, Content may be text, image, audio, or tool_result.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type SamplingMessage struct {
Content Content `json:"content"`
Role Role `json:"role"`
@ -1746,6 +1861,12 @@ func (m *SamplingMessage) UnmarshalJSON(data []byte) error {
return nil
}
// SetLoggingLevelParams holds parameters for a logging/setLevel request.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type SetLoggingLevelParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -2071,6 +2192,11 @@ type Implementation struct {
type CompletionCapabilities struct{}
// LoggingCapabilities describes the server's support for sending log messages to the client.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type LoggingCapabilities struct{}
// PromptCapabilities describes the server's support for prompts.
@ -2114,6 +2240,11 @@ type ServerCapabilities struct {
// suggestions.
Completions *CompletionCapabilities `json:"completions,omitempty"`
// Logging is present if the server supports log messages.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
Logging *LoggingCapabilities `json:"logging,omitempty"`
// Prompts is present if the server supports prompts.
Prompts *PromptCapabilities `json:"prompts,omitempty"`
@ -2196,6 +2327,11 @@ const (
// MetaKeyClientCapabilities carries the client's [ClientCapabilities].
MetaKeyClientCapabilities = "io.modelcontextprotocol/clientCapabilities"
// MetaKeyLogLevel identifies the desired log level for the request.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
MetaKeyLogLevel = "io.modelcontextprotocol/logLevel"
// MetaKeySubscriptionID identifies the subscriptions/listen request that an
// out-of-band notification belongs to.

2
mcp/sampling_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
//lint:file-ignore SA1019 tests exercise deprecated SEP-2577 sampling APIs.
package mcp
// TODO: move other sampling-related tests to this file.

49
mcp/server.go
View file

@ -73,6 +73,12 @@ type ServerOptions struct {
// If zero, defaults to [DefaultPageSize].
PageSize int
// If non-nil, called when "notifications/roots/list_changed" is received.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). Migrate to passing paths via tool
// parameters, resource URIs, or configuration. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
RootsListChangedHandler func(context.Context, *RootsListChangedRequest)
// If non-nil, called when "notifications/progress" is received.
ProgressNotificationHandler func(context.Context, *ProgressNotificationServerRequest)
@ -1474,6 +1480,12 @@ func (ss *ServerSession) Ping(ctx context.Context, params *PingParams) error {
}
// ListRoots lists the client roots.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). Migrate to passing paths via tool parameters,
// resource URIs, or configuration. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (ss *ServerSession) ListRoots(ctx context.Context, params *ListRootsParams) (*ListRootsResult, error) {
if err := ss.checkInitialized(methodListRoots); err != nil {
return nil, err
@ -1486,6 +1498,12 @@ func (ss *ServerSession) ListRoots(ctx context.Context, params *ListRootsParams)
// If the client returns multiple content blocks (e.g. parallel tool calls),
// CreateMessage returns an error. Use [ServerSession.CreateMessageWithTools]
// for tool-enabled sampling.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). Migrate to calling LLM provider APIs directly
// from your server. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (ss *ServerSession) CreateMessage(ctx context.Context, params *CreateMessageParams) (*CreateMessageResult, error) {
if err := ss.checkInitialized(methodCreateMessage); err != nil {
return nil, err
@ -1523,6 +1541,12 @@ func (ss *ServerSession) CreateMessage(ctx context.Context, params *CreateMessag
// returning a [CreateMessageWithToolsResult] that supports array content
// (for parallel tool calls). Use this instead of [ServerSession.CreateMessage]
// when the request includes tools.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). Migrate to calling LLM provider APIs directly
// from your server. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (ss *ServerSession) CreateMessageWithTools(ctx context.Context, params *CreateMessageWithToolsParams) (*CreateMessageWithToolsResult, error) {
if err := ss.checkInitialized(methodCreateMessage); err != nil {
return nil, err
@ -1609,28 +1633,21 @@ func (ss *ServerSession) Elicit(ctx context.Context, params *ElicitParams) (*Eli
return res, nil
}
// logLevelContextKey carries the per-request log level from
// [ServerSession.handle] to [ServerSession.Log] for new-protocol
// (>= 2026-07-28) requests. The level is scoped to a single in-flight request
// — including handler goroutines that call [ServerSession.Log] concurrently —
// rather than to the session, which avoids races between concurrent requests
// and aligns with SEP-2575's per-request opt-in model. The value type is
// [LoggingLevel]; an empty string means the request opted out of log messages.
type logLevelContextKey struct{}
// Log sends a log message to the client.
//
// For new-protocol (>= 2026-07-28) requests, the level is taken from the
// originating request's `_meta` field (SEP-2575); an absent or empty value
// suppresses the message per spec. For old-protocol requests, the level is
// taken from the session state set via `logging/setLevel`.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (ss *ServerSession) Log(ctx context.Context, params *LoggingMessageParams) error {
logLevel, ok := ctx.Value(logLevelContextKey{}).(LoggingLevel)
if !ok {
ss.mu.Lock()
logLevel = ss.state.LogLevel
ss.mu.Unlock()
}
ss.mu.Lock()
logLevel := ss.state.LogLevel
ss.mu.Unlock()
if logLevel == "" {
// The spec is unclear, but seems to imply that no log messages are sent until the client
// sets the level.
@ -1806,7 +1823,7 @@ func (ss *ServerSession) handle(ctx context.Context, req *jsonrpc.Request) (any,
ctx = context.WithValue(ctx, idContextKey{}, req.ID)
// For new-protocol requests, propagate the per-request log level.
if validatedMeta.usesNewProtocol {
ctx = context.WithValue(ctx, logLevelContextKey{}, validatedMeta.logLevel)
ss.setLevel(ctx, &SetLoggingLevelParams{Level: validatedMeta.logLevel})
}
return handleReceive(ctx, ss, req)
}

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