diff --git a/Makefile b/Makefile
index b4b33bdb5..4a1b4055f 100644
--- a/Makefile
+++ b/Makefile
@@ -8,7 +8,7 @@ ci-build: install proto http-api-docs
 install: grpc-install api-linter-install buf-install
 
 # Run all linters and compile proto files.
-proto: grpc http-api-docs
+proto: sync-nexus-annotations grpc http-api-docs nexusrpc-yaml
 ########################################################################
 
 ##### Variables ######
@@ -95,6 +95,11 @@ buf-install:
 	printf $(COLOR) "Install/update buf..."
 	go install github.com/bufbuild/buf/cmd/buf@v1.27.0
 
+##### Sync external proto dependencies #####
+sync-nexus-annotations:
+	printf $(COLOR) "Sync nexusannotations from buf.build/temporalio/nexus-annotations..."
+	buf export buf.build/temporalio/nexus-annotations --output .
+
 ##### Linters #####
 api-linter:
 	printf $(COLOR) "Run api-linter..."
@@ -116,6 +121,18 @@ buf-breaking:
 	@printf $(COLOR) "Run buf breaking changes check against master branch..."	
 	@(cd $(PROTO_ROOT) && buf breaking --against 'https://github.com/temporalio/api.git#branch=master')
 
+nexusrpc-yaml: nexusrpc-yaml-install
+	printf $(COLOR) "Generate nexus/nexusrpc.yaml and nexus/nexusrpc.langs.yaml..."
+	mkdir -p nexus
+	protoc -I $(PROTO_ROOT) \
+		--nexus-rpc-yaml_out=. \
+		temporal/api/workflowservice/v1/* \
+		temporal/api/operatorservice/v1/*
+
+nexusrpc-yaml-install:
+	printf $(COLOR) "Install protoc-gen-nexus-rpc-yaml..."
+	cd cmd/protoc-gen-nexus-rpc-yaml && go install .
+
 ##### Clean #####
 clean:
 	printf $(COLOR) "Delete generated go files..."
diff --git a/buf.lock b/buf.lock
index fccbfb89d..f43352bf2 100644
--- a/buf.lock
+++ b/buf.lock
@@ -4,10 +4,15 @@ deps:
   - remote: buf.build
     owner: googleapis
     repository: googleapis
-    commit: 28151c0d0a1641bf938a7672c500e01d
-    digest: shake256:49215edf8ef57f7863004539deff8834cfb2195113f0b890dd1f67815d9353e28e668019165b9d872395871eeafcbab3ccfdb2b5f11734d3cca95be9e8d139de
+    commit: 004180b77378443887d3b55cabc00384
+    digest: shake256:d26c7c2fd95f0873761af33ca4a0c0d92c8577122b6feb74eb3b0a57ebe47a98ab24a209a0e91945ac4c77204e9da0c2de0020b2cedc27bdbcdea6c431eec69b
   - remote: buf.build
     owner: grpc-ecosystem
     repository: grpc-gateway
-    commit: 048ae6ff94ca4476b3225904b1078fad
-    digest: shake256:e5250bf2d999516c02206d757502b902e406f35c099d0e869dc3e4f923f6870fe0805a9974c27df0695462937eae90cd4d9db90bb9a03489412560baa74a87b6
+    commit: 6467306b4f624747aaf6266762ee7a1c
+    digest: shake256:833d648b99b9d2c18b6882ef41aaeb113e76fc38de20dda810c588d133846e6593b4da71b388bcd921b1c7ab41c7acf8f106663d7301ae9e82ceab22cf64b1b7
+  - remote: buf.build
+    owner: temporalio
+    repository: nexus-annotations
+    commit: 599b78404fbe4e78b833d527a1d0da40
+    digest: shake256:1f41ef11ccbf31d7318b0fe1915550ba6567c99dc94694d60b117fc1ffc756290ba9766c58b403986f079e2b861b42538e5f8cf0495f744cd390d223b81854ca
diff --git a/buf.yaml b/buf.yaml
index e984c1439..6b9d9eb57 100644
--- a/buf.yaml
+++ b/buf.yaml
@@ -3,11 +3,14 @@ name: buf.build/temporalio/api
 deps:
   - buf.build/grpc-ecosystem/grpc-gateway
   - buf.build/googleapis/googleapis
+  - buf.build/temporalio/nexus-annotations
 build:
   excludes:
     # Buf won't accept a local dependency on the google protos but we need them
     # to run api-linter, so just tell buf it ignore it
     - google
+    # Same for nexusannotations - local copy for api-linter, BSR dep for buf
+    - nexusannotations
 breaking:
   use:
     - WIRE_JSON
diff --git a/cmd/protoc-gen-nexus-rpc-yaml/generator.go b/cmd/protoc-gen-nexus-rpc-yaml/generator.go
new file mode 100644
index 000000000..53fa78fe5
--- /dev/null
+++ b/cmd/protoc-gen-nexus-rpc-yaml/generator.go
@@ -0,0 +1,196 @@
+package main
+
+import (
+	"slices"
+	"sort"
+	"strings"
+
+	nexusannotationsv1 "github.com/nexus-rpc/nexus-proto-annotations/go/nexusannotations/v1"
+	"google.golang.org/protobuf/compiler/protogen"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/reflect/protoreflect"
+	"google.golang.org/protobuf/types/descriptorpb"
+	"gopkg.in/yaml.v3"
+)
+
+func generate(gen *protogen.Plugin) error {
+	nexusDoc := newDoc()
+	langsDoc := newDoc()
+
+	for _, f := range gen.Files {
+		if !f.Generate {
+			continue
+		}
+		for _, svc := range f.Services {
+			for _, m := range svc.Methods {
+				opts, ok := m.Desc.Options().(*descriptorpb.MethodOptions)
+				if !ok || opts == nil {
+					continue
+				}
+				if !proto.HasExtension(opts, nexusannotationsv1.E_Operation) {
+					continue
+				}
+				opOpts := proto.GetExtension(opts, nexusannotationsv1.E_Operation).(*nexusannotationsv1.OperationOptions)
+				if !slices.Contains(opOpts.GetTags(), "exposed") {
+					continue
+				}
+
+				svcName := string(svc.Desc.Name())
+				methodName := string(m.Desc.Name())
+
+				addOperation(nexusDoc, svcName, methodName,
+					map[string]string{"$ref": openAPIRef(m.Input.Desc)},
+					map[string]string{"$ref": openAPIRef(m.Output.Desc)},
+				)
+
+				addOperation(langsDoc, svcName, methodName,
+					langRefs(f.Desc, m.Input.Desc),
+					langRefs(f.Desc, m.Output.Desc),
+				)
+			}
+		}
+	}
+
+	if err := writeFile(gen, "nexus/nexusrpc.yaml", nexusDoc); err != nil {
+		return err
+	}
+	return writeFile(gen, "nexus/nexusrpc.langs.yaml", langsDoc)
+}
+
+// openAPIRef returns the nexus-rpc-gen multi-file $ref string for a message type,
+// referencing the openapiv3.yaml components/schemas entry. The path is relative to nexus/.
+//
+// Schema key convention used by protoc-gen-openapi (v3):
+//
+//	{MessageName}  (no package prefix)
+//
+// e.g. message "SignalWithStartWorkflowExecutionRequest"
+// → "../openapi/openapiv3.yaml#/components/schemas/SignalWithStartWorkflowExecutionRequest"
+func openAPIRef(msg protoreflect.MessageDescriptor) string {
+	return "../openapi/openapiv3.yaml#/components/schemas/" + string(msg.Name())
+}
+
+// langRefs builds the map of language-specific type refs for a message,
+// derived from proto file-level options. Only keys with non-empty values are included.
+// Order is canonical: go → java → ruby → csharp.
+func langRefs(file protoreflect.FileDescriptor, msg protoreflect.MessageDescriptor) map[string]string {
+	opts, ok := file.Options().(*descriptorpb.FileOptions)
+	if !ok || opts == nil {
+		return nil
+	}
+	name := string(msg.Name())
+	refs := make(map[string]string)
+
+	if pkg := opts.GetGoPackage(); pkg != "" {
+		// strip the ";alias" suffix (e.g. "go.temporal.io/api/workflowservice/v1;workflowservice")
+		pkg = strings.SplitN(pkg, ";", 2)[0]
+		refs["$goRef"] = pkg + "." + name
+	}
+	if pkg := opts.GetJavaPackage(); pkg != "" {
+		refs["$javaRef"] = pkg + "." + name
+	}
+	if pkg := opts.GetRubyPackage(); pkg != "" {
+		refs["$rubyRef"] = pkg + "::" + name
+	}
+	if pkg := opts.GetCsharpNamespace(); pkg != "" {
+		refs["$csharpRef"] = pkg + "." + name
+	}
+	if len(refs) == 0 {
+		return nil
+	}
+	return refs
+}
+
+// newDoc creates a yaml.Node document with the "nexusrpc: 1.0.0" header
+// and an empty "services" mapping node, returned as a *yaml.Node (document node).
+func newDoc() *yaml.Node {
+	doc := &yaml.Node{Kind: yaml.DocumentNode}
+	root := &yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"}
+	doc.Content = []*yaml.Node{root}
+
+	root.Content = append(root.Content,
+		scalarNode("nexusrpc"),
+		scalarNode("1.0.0"),
+		scalarNode("services"),
+		&yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"},
+	)
+	return doc
+}
+
+// servicesNode returns the "services" mapping node from a doc created by newDoc.
+func servicesNode(doc *yaml.Node) *yaml.Node {
+	root := doc.Content[0]
+	for i := 0; i < len(root.Content)-1; i += 2 {
+		if root.Content[i].Value == "services" {
+			return root.Content[i+1]
+		}
+	}
+	panic("services node not found")
+}
+
+// addOperation inserts a service → operation → {input, output} entry into doc.
+// Services and operations are inserted in the order first encountered.
+func addOperation(doc *yaml.Node, svcName, methodName string, input, output map[string]string) {
+	svcs := servicesNode(doc)
+
+	// find or create service node
+	var svcOps *yaml.Node
+	for i := 0; i < len(svcs.Content)-1; i += 2 {
+		if svcs.Content[i].Value == svcName {
+			// find "operations" within service mapping
+			svcMap := svcs.Content[i+1]
+			for j := 0; j < len(svcMap.Content)-1; j += 2 {
+				if svcMap.Content[j].Value == "operations" {
+					svcOps = svcMap.Content[j+1]
+				}
+			}
+		}
+	}
+	if svcOps == nil {
+		svcMap := &yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"}
+		svcOps = &yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"}
+		svcMap.Content = append(svcMap.Content,
+			scalarNode("operations"),
+			svcOps,
+		)
+		svcs.Content = append(svcs.Content, scalarNode(svcName), svcMap)
+	}
+
+	// build operation node
+	opNode := &yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"}
+	if len(input) > 0 {
+		opNode.Content = append(opNode.Content, scalarNode("input"), mapNode(input))
+	}
+	if len(output) > 0 {
+		opNode.Content = append(opNode.Content, scalarNode("output"), mapNode(output))
+	}
+	svcOps.Content = append(svcOps.Content, scalarNode(methodName), opNode)
+}
+
+// mapNode serializes a map[string]string as a yaml mapping node with keys in sorted order.
+func mapNode(m map[string]string) *yaml.Node {
+	keys := make([]string, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	node := &yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"}
+	for _, k := range keys {
+		node.Content = append(node.Content, scalarNode(k), scalarNode(m[k]))
+	}
+	return node
+}
+
+func scalarNode(value string) *yaml.Node {
+	return &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: value}
+}
+
+func writeFile(gen *protogen.Plugin, name string, doc *yaml.Node) error {
+	f := gen.NewGeneratedFile(name, "")
+	enc := yaml.NewEncoder(f)
+	enc.SetIndent(2)
+	if err := enc.Encode(doc); err != nil {
+		return err
+	}
+	return enc.Close()
+}
diff --git a/cmd/protoc-gen-nexus-rpc-yaml/go.mod b/cmd/protoc-gen-nexus-rpc-yaml/go.mod
new file mode 100644
index 000000000..610f91712
--- /dev/null
+++ b/cmd/protoc-gen-nexus-rpc-yaml/go.mod
@@ -0,0 +1,10 @@
+module github.com/temporalio/api/cmd/protoc-gen-nexus-rpc-yaml
+
+go 1.25.4
+
+require (
+	google.golang.org/protobuf v1.36.1
+	gopkg.in/yaml.v3 v3.0.1
+)
+
+require github.com/nexus-rpc/nexus-proto-annotations v0.0.0-20260330194009-e558d6edaf84
diff --git a/cmd/protoc-gen-nexus-rpc-yaml/go.sum b/cmd/protoc-gen-nexus-rpc-yaml/go.sum
new file mode 100644
index 000000000..f9fd894ce
--- /dev/null
+++ b/cmd/protoc-gen-nexus-rpc-yaml/go.sum
@@ -0,0 +1,12 @@
+github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
+github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/nexus-rpc/nexus-proto-annotations v0.0.0-20260330194009-e558d6edaf84 h1:SWHt3Coj0VvF0Km1A0wlY+IjnHKsjQLgO29io84r3wY=
+github.com/nexus-rpc/nexus-proto-annotations v0.0.0-20260330194009-e558d6edaf84/go.mod h1:n3UjF1bPCW8llR8tHvbxJ+27yPWrhpo8w/Yg1IOuY0Y=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+google.golang.org/protobuf v1.36.1 h1:yBPeRvTftaleIgM3PZ/WBIZ7XM/eEYAaEyCwvyjq/gk=
+google.golang.org/protobuf v1.36.1/go.mod h1:9fA7Ob0pmnwhb644+1+CVWFRbNajQ6iRojtC/QF5bRE=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/cmd/protoc-gen-nexus-rpc-yaml/main.go b/cmd/protoc-gen-nexus-rpc-yaml/main.go
new file mode 100644
index 000000000..9fadd0fb1
--- /dev/null
+++ b/cmd/protoc-gen-nexus-rpc-yaml/main.go
@@ -0,0 +1,14 @@
+// protoc-gen-nexus-rpc-yaml is a protoc plugin that generates nexus/nexusrpc.yaml
+// and nexus/nexusrpc.langs.yaml from proto service methods annotated with
+// option (nexusannotations.v1.operation).tags = "exposed".
+package main
+
+import (
+	"google.golang.org/protobuf/compiler/protogen"
+)
+
+func main() {
+	protogen.Options{}.Run(func(gen *protogen.Plugin) error {
+		return generate(gen)
+	})
+}
diff --git a/nexus/nexusrpc.langs.yaml b/nexus/nexusrpc.langs.yaml
new file mode 100644
index 000000000..2262cf57d
--- /dev/null
+++ b/nexus/nexusrpc.langs.yaml
@@ -0,0 +1,15 @@
+nexusrpc: 1.0.0
+services:
+  WorkflowService:
+    operations:
+      SignalWithStartWorkflowExecution:
+        input:
+          $csharpRef: Temporalio.Api.WorkflowService.V1.SignalWithStartWorkflowExecutionRequest
+          $goRef: go.temporal.io/api/workflowservice/v1.SignalWithStartWorkflowExecutionRequest
+          $javaRef: io.temporal.api.workflowservice.v1.SignalWithStartWorkflowExecutionRequest
+          $rubyRef: Temporalio::Api::WorkflowService::V1::SignalWithStartWorkflowExecutionRequest
+        output:
+          $csharpRef: Temporalio.Api.WorkflowService.V1.SignalWithStartWorkflowExecutionResponse
+          $goRef: go.temporal.io/api/workflowservice/v1.SignalWithStartWorkflowExecutionResponse
+          $javaRef: io.temporal.api.workflowservice.v1.SignalWithStartWorkflowExecutionResponse
+          $rubyRef: Temporalio::Api::WorkflowService::V1::SignalWithStartWorkflowExecutionResponse
diff --git a/nexus/nexusrpc.yaml b/nexus/nexusrpc.yaml
new file mode 100644
index 000000000..bbfafb33a
--- /dev/null
+++ b/nexus/nexusrpc.yaml
@@ -0,0 +1,9 @@
+nexusrpc: 1.0.0
+services:
+  WorkflowService:
+    operations:
+      SignalWithStartWorkflowExecution:
+        input:
+          $ref: ../openapi/openapiv3.yaml#/components/schemas/SignalWithStartWorkflowExecutionRequest
+        output:
+          $ref: ../openapi/openapiv3.yaml#/components/schemas/SignalWithStartWorkflowExecutionResponse
diff --git a/nexusannotations/v1/options.proto b/nexusannotations/v1/options.proto
new file mode 100644
index 000000000..e137896bb
--- /dev/null
+++ b/nexusannotations/v1/options.proto
@@ -0,0 +1,29 @@
+syntax = "proto3";
+
+package nexusannotations.v1;
+
+import "google/protobuf/descriptor.proto";
+
+option go_package = "github.com/nexus-rpc/nexus-proto-annotations/go/nexusannotations/v1";
+
+extend google.protobuf.ServiceOptions {
+  optional ServiceOptions service = 8233;
+}
+
+extend google.protobuf.MethodOptions {
+  optional OperationOptions operation = 8234;
+}
+
+message OperationOptions {
+  // Nexus operation name (defaults to proto method name).
+  string name = 1;
+  // Tags to attach to the operation. Used by code generators to include and exclude operations.
+  repeated string tags = 2;
+}
+
+message ServiceOptions {
+  // Nexus service name (defaults to proto service full name).
+  string name = 1;
+  // Tags to attach to the service. Used by code generators to include and exclude services.
+  repeated string tags = 2;
+}
diff --git a/temporal/api/workflowservice/v1/service.proto b/temporal/api/workflowservice/v1/service.proto
index 18e579c2c..cfe44d4ef 100644
--- a/temporal/api/workflowservice/v1/service.proto
+++ b/temporal/api/workflowservice/v1/service.proto
@@ -10,9 +10,10 @@ option ruby_package = "Temporalio::Api::WorkflowService::V1";
 option csharp_namespace = "Temporalio.Api.WorkflowService.V1";
 
 
-import "temporal/api/workflowservice/v1/request_response.proto";
 import "google/api/annotations.proto";
+import "nexusannotations/v1/options.proto";
 import "temporal/api/protometa/v1/annotations.proto";
+import "temporal/api/workflowservice/v1/request_response.proto";
 
 // WorkflowService API defines how Temporal SDKs and other clients interact with the Temporal server
 // to create and interact with workflows and activities.
@@ -487,6 +488,8 @@ service WorkflowService {
     // (-- api-linter: core::0136::prepositions=disabled
     //     aip.dev/not-precedent: "With" is used to indicate combined operation. --)
     rpc SignalWithStartWorkflowExecution (SignalWithStartWorkflowExecutionRequest) returns (SignalWithStartWorkflowExecutionResponse) {
+        option (nexusannotations.v1.operation).tags = "exposed";
+
         option (google.api.http) = {
             post: "/namespaces/{namespace}/workflows/{workflow_id}/signal-with-start/{signal_name}"
             body: "*"