diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3ee272369c8..05c0b540902 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -32,6 +32,34 @@
   strategy, given that the code would eventually become ambiguous anyways when
   the deployment target is raised.
 
+* [SE-0470][]:
+  A protocol conformance can be isolated to a specific global actor, meaning that the conformance can only be used by code running on that actor. Isolated conformances are expressed by specifying the global actor on the conformance itself:
+
+  ```swift
+  protocol P {
+    func f()
+  }
+
+  @MainActor
+  class MyType: @MainActor P {
+    /*@MainActor*/ func f() {
+      // must be called on the main actor
+    }
+  }
+  ```
+
+  Swift will produce diagnostics if the conformance is directly accessed in code that isn't guaranteed to execute in the same global actor. For example:
+
+  ```swift
+  func acceptP<T: P>(_ value: T) { }
+
+  /*nonisolated*/ func useIsolatedConformance(myType: MyType) {
+    acceptP(myType) // error: main actor-isolated conformance of 'MyType' to 'P' cannot be used in nonisolated context
+  }
+  ```
+
+  To address such issues, only use an isolated conformance from code that executes on the same global actor.
+
 * [SE-0419][]:
   Introduced the new `Runtime` module, which contains a public API that can
   generate backtraces, presently supported on macOS and Linux.  Capturing a
@@ -10759,6 +10787,7 @@ using the `.dynamicType` member to retrieve the type of an expression should mig
 [SE-0442]: https://github.com/swiftlang/swift-evolution/blob/main/proposals/0442-allow-taskgroup-childtaskresult-type-to-be-inferred.md
 [SE-0444]: https://github.com/swiftlang/swift-evolution/blob/main/proposals/0444-member-import-visibility.md
 [SE-0458]: https://github.com/swiftlang/swift-evolution/blob/main/proposals/0458-strict-memory-safety.md
+[SE-0470]: https://github.com/swiftlang/swift-evolution/blob/main/proposals/0470-isolated-conformances.md
 [#64927]: <https://github.com/apple/swift/issues/64927>
 [#42697]: <https://github.com/apple/swift/issues/42697>
 [#42728]: <https://github.com/apple/swift/issues/42728>
diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
index 12c44ff07a0..062b5bf76f1 100644
--- a/include/swift/AST/DiagnosticsSema.def
+++ b/include/swift/AST/DiagnosticsSema.def
@@ -8486,10 +8486,6 @@ ERROR(attr_abi_failable_mismatch,none,
 //===----------------------------------------------------------------------===//
 // MARK: Isolated conformances
 //===----------------------------------------------------------------------===//
-GROUPED_ERROR(isolated_conformance_experimental_feature,IsolatedConformances,
-      none,
-      "isolated conformances require experimental feature "
-      " 'IsolatedConformances'", ())
 NOTE(note_isolate_conformance_to_global_actor,none,
      "isolate this conformance to the %select{global actor %0|main actor}1 "
      "with '@%2'", (Type, bool, StringRef))
diff --git a/include/swift/Basic/Features.def b/include/swift/Basic/Features.def
index 21e3af02aeb..b3c01fcf0eb 100644
--- a/include/swift/Basic/Features.def
+++ b/include/swift/Basic/Features.def
@@ -254,6 +254,7 @@ SUPPRESSIBLE_LANGUAGE_FEATURE(MemorySafetyAttributes, 458, "@unsafe attribute")
 LANGUAGE_FEATURE(ValueGenerics, 452, "Value generics feature (integer generics)")
 LANGUAGE_FEATURE(RawIdentifiers, 451, "Raw identifiers")
 LANGUAGE_FEATURE(SendableCompletionHandlers, 463, "Objective-C completion handler parameters are imported as @Sendable")
+LANGUAGE_FEATURE(IsolatedConformances, 407, "Global-actor isolated conformances")
 
 // Swift 6
 UPCOMING_FEATURE(ConciseMagicFile, 274, 6)
@@ -276,6 +277,7 @@ UPCOMING_FEATURE(GlobalActorIsolatedTypesUsability, 0434, 6)
 ADOPTABLE_UPCOMING_FEATURE(ExistentialAny, 335, 7)
 UPCOMING_FEATURE(InternalImportsByDefault, 409, 7)
 UPCOMING_FEATURE(MemberImportVisibility, 444, 7)
+UPCOMING_FEATURE(InferIsolatedConformances, 470, 7)
 
 // Optional language features / modes
 
@@ -495,6 +497,7 @@ ADOPTABLE_EXPERIMENTAL_FEATURE(AsyncCallerExecution, false)
 /// Allow custom availability domains to be defined and referenced.
 EXPERIMENTAL_FEATURE(CustomAvailability, true)
 
+<<<<<<< HEAD
 /// Allow public enumerations to be extensible by default
 /// regardless of whether the module they are declared in
 /// is resilient or not.
@@ -506,6 +509,8 @@ EXPERIMENTAL_FEATURE(IsolatedConformances, true)
 /// Infer conformance isolation on global-actor-conforming types.
 EXPERIMENTAL_FEATURE(InferIsolatedConformances, true)
 
+=======
+>>>>>>> 3380331e7eb ([SE-0470] Enable isolated conformances by default)
 /// Allow SwiftSettings
 EXPERIMENTAL_FEATURE(SwiftSettings, false)
 
diff --git a/lib/AST/ConformanceLookup.cpp b/lib/AST/ConformanceLookup.cpp
index dc02e369d7d..93d78317219 100644
--- a/lib/AST/ConformanceLookup.cpp
+++ b/lib/AST/ConformanceLookup.cpp
@@ -386,33 +386,30 @@ static ProtocolConformanceRef getBuiltinMetaTypeTypeConformance(
   // All metatypes are Copyable, Escapable, and BitwiseCopyable.
   if (auto kp = protocol->getKnownProtocolKind()) {
     switch (*kp) {
-    case KnownProtocolKind::Sendable:
+    case KnownProtocolKind::Sendable: {
       // Metatypes are generally Sendable, but with isolated conformances we
       // cannot assume that metatypes based on type parameters are Sendable.
       // Therefore, check for conformance to SendableMetatype.
-      if (ctx.LangOpts.hasFeature(Feature::IsolatedConformances)) {
-        auto sendableMetatypeProto = 
-            ctx.getProtocol(KnownProtocolKind::SendableMetatype);
-        if (sendableMetatypeProto) {
-          Type instanceType = metatypeType->getInstanceType();
+      auto sendableMetatypeProto =
+          ctx.getProtocol(KnownProtocolKind::SendableMetatype);
+      if (sendableMetatypeProto) {
+        Type instanceType = metatypeType->getInstanceType();
 
-          // If the instance type is a type parameter, it is not necessarily
-          // Sendable. There will need to be a Sendable requirement.
-          if (instanceType->isTypeParameter())
-            break;
+        // If the instance type is a type parameter, it is not necessarily
+        // Sendable. There will need to be a Sendable requirement.
+        if (instanceType->isTypeParameter())
+          break;
 
-          // If the instance type conforms to SendableMetatype, then its
-          // metatype is Sendable.
-          auto instanceConformance = lookupConformance(
-              instanceType, sendableMetatypeProto);
-          if (instanceConformance.isInvalid() ||
-              instanceConformance.hasMissingConformance())
-            break;
-        }
-
-        // Every other metatype is Sendable.
+        // If the instance type conforms to SendableMetatype, then its
+        // metatype is Sendable.
+        auto instanceConformance = lookupConformance(
+            instanceType, sendableMetatypeProto);
+        if (instanceConformance.isInvalid() ||
+            instanceConformance.hasMissingConformance())
+          break;
       }
       LLVM_FALLTHROUGH;
+    }
 
     case KnownProtocolKind::Copyable:
     case KnownProtocolKind::Escapable:
diff --git a/lib/Parse/ParseType.cpp b/lib/Parse/ParseType.cpp
index 414b6056bac..5ac469fe59c 100644
--- a/lib/Parse/ParseType.cpp
+++ b/lib/Parse/ParseType.cpp
@@ -163,9 +163,7 @@ ParserResult<TypeRepr> Parser::parseTypeSimple(
     Diag<> MessageID, ParseTypeReason reason) {
   ParserResult<TypeRepr> ty;
 
-  if (isParameterSpecifier() &&
-      !(!Context.LangOpts.hasFeature(Feature::IsolatedConformances) &&
-        Tok.isContextualKeyword("isolated"))) {
+  if (isParameterSpecifier()) {
     // Type specifier should already be parsed before here. This only happens
     // for construct like 'P1 & inout P2'.
     diagnose(Tok.getLoc(), diag::attr_only_on_parameters, Tok.getRawText());
diff --git a/lib/Sema/TypeCheckConcurrency.cpp b/lib/Sema/TypeCheckConcurrency.cpp
index 640911ae563..fc32dad4122 100644
--- a/lib/Sema/TypeCheckConcurrency.cpp
+++ b/lib/Sema/TypeCheckConcurrency.cpp
@@ -3021,10 +3021,9 @@ namespace {
       // FIXME: When passing to a sending parameter, should this be handled
       // by region isolation? Or should it always be handled by region
       // isolation?
-      if (ctx.LangOpts.hasFeature(Feature::IsolatedConformances) &&
-          (mayExecuteConcurrentlyWith(
+      if (mayExecuteConcurrentlyWith(
               localFunc.getAsDeclContext(), getDeclContext()) ||
-           (explicitClosure && explicitClosure->isPassedToSendingParameter()))) {
+          (explicitClosure && explicitClosure->isPassedToSendingParameter())) {
         GenericSignature genericSig;
         if (auto afd = localFunc.getAbstractFunctionDecl())
           genericSig = afd->getGenericSignature();
@@ -7931,8 +7930,6 @@ ConformanceIsolationRequest::evaluate(Evaluator &evaluator, ProtocolConformance
 
   auto dc = rootNormal->getDeclContext();
   ASTContext &ctx = dc->getASTContext();
-  if (!ctx.LangOpts.hasFeature(Feature::IsolatedConformances))
-    return ActorIsolation::forNonisolated(false);
 
   // If the protocol itself is isolated, don't infer isolation for the
   // conformance.
diff --git a/lib/Sema/TypeCheckProtocol.cpp b/lib/Sema/TypeCheckProtocol.cpp
index 13abba03c1d..d12803a8554 100644
--- a/lib/Sema/TypeCheckProtocol.cpp
+++ b/lib/Sema/TypeCheckProtocol.cpp
@@ -2567,13 +2567,6 @@ checkIndividualConformance(NormalProtocolConformance *conformance) {
       ComplainLoc, diag::unchecked_conformance_not_special, ProtoType);
   }
 
-  // Complain if the global-actor-isolated conformances are not enabled.
-  if (conformance->isIsolated() &&
-      !Context.LangOpts.hasFeature(Feature::IsolatedConformances)) {
-    Context.Diags.diagnose(
-        ComplainLoc, diag::isolated_conformance_experimental_feature);
-  }
-  
   bool allowImpliedConditionalConformance = false;
   if (Proto->isSpecificProtocol(KnownProtocolKind::Sendable)) {
     // In -swift-version 5 mode, a conditional conformance to a protocol can imply
@@ -4978,8 +4971,7 @@ static void diagnoseConformanceIsolationErrors(
     }
 
     // Suggest isolating the conformance, if possible.
-    if (ctx.LangOpts.hasFeature(Feature::IsolatedConformances) &&
-        potentialIsolation && potentialIsolation->isGlobalActor() &&
+    if (potentialIsolation && potentialIsolation->isGlobalActor() &&
         !conformance->isIsolated()) {
       bool isMainActor = false;
       Type globalActorIsolation = potentialIsolation->getGlobalActor();
diff --git a/test/Concurrency/Runtime/isolated_conformance.swift b/test/Concurrency/Runtime/isolated_conformance.swift
index ca3a3534404..bc795e22e59 100644
--- a/test/Concurrency/Runtime/isolated_conformance.swift
+++ b/test/Concurrency/Runtime/isolated_conformance.swift
@@ -1,9 +1,8 @@
-// RUN: %target-run-simple-swift(-enable-experimental-feature IsolatedConformances -target %target-swift-5.1-abi-triple) | %FileCheck %s
+// RUN: %target-run-simple-swift(-target %target-swift-5.1-abi-triple) | %FileCheck %s
 
 // REQUIRES: executable_test
 // REQUIRES: concurrency
 // REQUIRES: concurrency_runtime
-// REQUIRES: swift_feature_IsolatedConformances
 // UNSUPPORTED: back_deployment_runtime
 
 // FIXME: WebAssembly doesn't currently have a good way to install the
diff --git a/test/Concurrency/isolated_conformance.swift b/test/Concurrency/isolated_conformance.swift
index dd6416ec171..92343133eaa 100644
--- a/test/Concurrency/isolated_conformance.swift
+++ b/test/Concurrency/isolated_conformance.swift
@@ -1,6 +1,5 @@
-// RUN: %target-swift-frontend -typecheck -verify -target %target-swift-5.1-abi-triple -swift-version 5 -strict-concurrency=complete -enable-experimental-feature IsolatedConformances %s
+// RUN: %target-swift-frontend -typecheck -verify -target %target-swift-5.1-abi-triple -swift-version 5 -strict-concurrency=complete %s
 
-// REQUIRES: swift_feature_IsolatedConformances
 // REQUIRES: concurrency
 
 protocol P {
diff --git a/test/Concurrency/isolated_conformance_default_actor.swift b/test/Concurrency/isolated_conformance_default_actor.swift
index 3b302234207..ce8cce07ecc 100644
--- a/test/Concurrency/isolated_conformance_default_actor.swift
+++ b/test/Concurrency/isolated_conformance_default_actor.swift
@@ -1,6 +1,5 @@
-// RUN: %target-swift-frontend -typecheck -verify -target %target-swift-5.1-abi-triple -swift-version 6 -enable-experimental-feature IsolatedConformances -default-isolation MainActor %s
+// RUN: %target-swift-frontend -typecheck -verify -target %target-swift-5.1-abi-triple -swift-version 6 -default-isolation MainActor %s
 
-// REQUIRES: swift_feature_IsolatedConformances
 // REQUIRES: concurrency
 
 nonisolated
diff --git a/test/Concurrency/isolated_conformance_inference.swift b/test/Concurrency/isolated_conformance_inference.swift
index ed0bc91ac2a..e513f3f8a77 100644
--- a/test/Concurrency/isolated_conformance_inference.swift
+++ b/test/Concurrency/isolated_conformance_inference.swift
@@ -1,7 +1,5 @@
-// RUN: %target-swift-frontend -typecheck -verify -target %target-swift-5.1-abi-triple -swift-version 6 -enable-experimental-feature IsolatedConformances -enable-experimental-feature InferIsolatedConformances %s
+// RUN: %target-swift-frontend -typecheck -verify -target %target-swift-5.1-abi-triple -swift-version 6 -enable-upcoming-feature InferIsolatedConformances %s
 
-// REQUIRES: swift_feature_IsolatedConformances
-// REQUIRES: swift_feature_InferIsolatedConformances
 // REQUIRES: concurrency
 
 protocol P {
diff --git a/test/Concurrency/sendable_metatype.swift b/test/Concurrency/sendable_metatype.swift
index a21366ac6f0..1371456d97e 100644
--- a/test/Concurrency/sendable_metatype.swift
+++ b/test/Concurrency/sendable_metatype.swift
@@ -1,7 +1,6 @@
-// RUN: %target-typecheck-verify-swift -swift-version 6 -enable-experimental-feature IsolatedConformances -emit-sil -o /dev/null
+// RUN: %target-typecheck-verify-swift -swift-version 6 -emit-sil -o /dev/null
 
 // REQUIRES: concurrency
-// REQUIRES: swift_feature_IsolatedConformances
 
 
 protocol Q {
diff --git a/test/Concurrency/sendable_metatype_typecheck.swift b/test/Concurrency/sendable_metatype_typecheck.swift
index 6ba6def4956..494ab2b8c9c 100644
--- a/test/Concurrency/sendable_metatype_typecheck.swift
+++ b/test/Concurrency/sendable_metatype_typecheck.swift
@@ -1,7 +1,6 @@
-// RUN: %target-typecheck-verify-swift -swift-version 6 -enable-experimental-feature IsolatedConformances
+// RUN: %target-typecheck-verify-swift -swift-version 6
 
 // REQUIRES: concurrency
-// REQUIRES: swift_feature_IsolatedConformances
 
 // This test checks for typecheck-only diagnostics involving non-sendable
 // metatypes.
diff --git a/test/IRGen/isolated_conformance.swift b/test/IRGen/isolated_conformance.swift
index 6240933188e..6900cf90573 100644
--- a/test/IRGen/isolated_conformance.swift
+++ b/test/IRGen/isolated_conformance.swift
@@ -1,8 +1,7 @@
-// RUN: %target-swift-frontend -primary-file %s -emit-ir -swift-version 6 -enable-experimental-feature IsolatedConformances | %FileCheck %s -DINT=i%target-ptrsize
+// RUN: %target-swift-frontend -primary-file %s -emit-ir -swift-version 6 | %FileCheck %s -DINT=i%target-ptrsize
 
 // REQUIRES: PTRSIZE=64
 // REQUIRES: concurrency
-// REQUIRES: swift_feature_IsolatedConformances
 // UNSUPPORTED: CPU=arm64e
 
 protocol P {
diff --git a/test/ModuleInterface/isolated_conformance.swift b/test/ModuleInterface/isolated_conformance.swift
index 23d93fcdd45..9ed21b8b67e 100644
--- a/test/ModuleInterface/isolated_conformance.swift
+++ b/test/ModuleInterface/isolated_conformance.swift
@@ -1,6 +1,5 @@
-// RUN: %target-swift-frontend -typecheck -swift-version 6 -enable-library-evolution -module-name isolated_conformance -enable-experimental-feature IsolatedConformances -emit-module-interface-path - %s | %FileCheck %s
+// RUN: %target-swift-frontend -typecheck -swift-version 6 -enable-library-evolution -module-name isolated_conformance -emit-module-interface-path - %s | %FileCheck %s
 
-// REQUIRES: swift_feature_IsolatedConformances
 // REQUIRES: concurrency
 
 public protocol MyProtocol {
diff --git a/test/SILOptimizer/constant_propagation_casts_ossa.sil b/test/SILOptimizer/constant_propagation_casts_ossa.sil
index c2ce3a3cfc8..875d0c9c7ab 100644
--- a/test/SILOptimizer/constant_propagation_casts_ossa.sil
+++ b/test/SILOptimizer/constant_propagation_casts_ossa.sil
@@ -1,6 +1,5 @@
-// RUN: %target-sil-opt -enable-sil-verify-all %s -diagnostic-constant-propagation -enable-experimental-feature IsolatedConformances | %FileCheck %s
+// RUN: %target-sil-opt -enable-sil-verify-all %s -diagnostic-constant-propagation | %FileCheck %s
 
-// REQUIRES: swift_feature_IsolatedConformances
 // REQUIRES: concurrency
 
 sil_stage canonical
diff --git a/test/SILOptimizer/isolated_conformances.swift b/test/SILOptimizer/isolated_conformances.swift
index f51da74545c..2c5e66d0942 100644
--- a/test/SILOptimizer/isolated_conformances.swift
+++ b/test/SILOptimizer/isolated_conformances.swift
@@ -1,14 +1,14 @@
 // RUN: %empty-directory(%t) 
-// RUN: %target-build-swift -parse-as-library -O %s -enable-experimental-feature IsolatedConformances -o %t/a.out
+// RUN: %target-build-swift -parse-as-library -O %s -o %t/a.out
 // RUN: %target-codesign %t/a.out
 // RUN: %target-run %t/a.out | %FileCheck %s --check-prefix=CHECK-OUTPUT
 
-// RUN: %target-build-swift -parse-as-library -O %s -enable-experimental-feature IsolatedConformances -Xllvm -sil-disable-pass=function-signature-opts -emit-sil | %FileCheck %s
+// RUN: %target-build-swift -parse-as-library -O %s -Xllvm -sil-disable-pass=function-signature-opts -emit-sil | %FileCheck %s
 
 // REQUIRES: concurrency
 // REQUIRES: executable_test
 // REQUIRES: concurrency_runtime
-// REQUIRES: swift_feature_IsolatedConformances
+// REQUIRES: OS=macosx || OS=linux-gnu
 
 // UNSUPPORTED: back_deployment_runtime
 // UNSUPPORTED: back_deploy_concurrency
diff --git a/test/SILOptimizer/simplify_unconditional_check_cast.sil b/test/SILOptimizer/simplify_unconditional_check_cast.sil
index 21134ec91a0..1b667b2e60d 100644
--- a/test/SILOptimizer/simplify_unconditional_check_cast.sil
+++ b/test/SILOptimizer/simplify_unconditional_check_cast.sil
@@ -1,6 +1,5 @@
-// RUN: %target-sil-opt -enable-sil-verify-all %s -simplification -simplify-instruction=unconditional_checked_cast -enable-experimental-feature IsolatedConformances | %FileCheck %s
+// RUN: %target-sil-opt -enable-sil-verify-all %s -simplification -simplify-instruction=unconditional_checked_cast | %FileCheck %s
 
-// REQUIRES: swift_feature_IsolatedConformances
 // REQUIRES: concurrency
 
 import Swift
diff --git a/test/Serialization/isolated_conformance.swift b/test/Serialization/isolated_conformance.swift
index beeb48aa106..064bdf03345 100644
--- a/test/Serialization/isolated_conformance.swift
+++ b/test/Serialization/isolated_conformance.swift
@@ -1,9 +1,8 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend -emit-module -target %target-swift-5.1-abi-triple -swift-version 6 -enable-experimental-feature IsolatedConformances -o %t/def_isolated_conformance.swiftmodule %S/Inputs/def_isolated_conformance.swift
+// RUN: %target-swift-frontend -emit-module -target %target-swift-5.1-abi-triple -swift-version 6 -o %t/def_isolated_conformance.swiftmodule %S/Inputs/def_isolated_conformance.swift
 
-// RUN: %target-swift-frontend -typecheck -verify -target %target-swift-5.1-abi-triple -swift-version 6 -enable-experimental-feature IsolatedConformances %s -I %t
+// RUN: %target-swift-frontend -typecheck -verify -target %target-swift-5.1-abi-triple -swift-version 6 %s -I %t
 
-// REQUIRES: swift_feature_IsolatedConformances
 // REQUIRES: concurrency
 
 import def_isolated_conformance