diff --git a/LaunchDarkly/LaunchDarkly/LDClient.swift b/LaunchDarkly/LaunchDarkly/LDClient.swift
index 6b61a2f1..6fbf04a8 100644
--- a/LaunchDarkly/LaunchDarkly/LDClient.swift
+++ b/LaunchDarkly/LaunchDarkly/LDClient.swift
@@ -107,7 +107,7 @@ public class LDClient {
      - parameter goOnline:    Desired online/offline mode for the LDClient
      - parameter completion:  Completion closure called when setOnline completes (Optional)
      */
-    public func setOnline(_ goOnline: Bool, completion: (() -> Void)? = nil) {
+    public func setOnline(_ goOnline: Bool, completion: (@Sendable() -> Void)? = nil) {
         let dispatch = DispatchGroup()
         LDClient.instancesQueue.sync(flags: .barrier) {
             LDClient.instances?.forEach { _, instance in
@@ -289,7 +289,7 @@ public class LDClient {
      - parameter completion: Closure called when the embedded `setOnlineIdentify` call completes, subject to throttling delays. (Optional)
     */
     @available(*, deprecated, message: "Use LDClient.identify(context: completion:) with non-optional completion parameter")
-    public func identify(context: LDContext, completion: (() -> Void)? = nil) {
+    public func identify(context: LDContext, completion: (@Sendable () -> Void)? = nil) {
         _identify(context: context, sheddable: false, useCache: .yes) { _ in
             if let completion = completion {
                 completion()
@@ -312,7 +312,7 @@ public class LDClient {
      - parameter context: The LDContext set with the desired context.
      - parameter completion: Closure called when the embedded `setOnlineIdentify` call completes, subject to throttling delays.
      */
-    public func identify(context: LDContext, completion: @escaping (_ result: IdentifyResult) -> Void) {
+    public func identify(context: LDContext, completion: @escaping @Sendable (_ result: IdentifyResult) -> Void) {
         _identify(context: context, sheddable: true, useCache: .yes, completion: completion)
     }
 
@@ -326,7 +326,7 @@ public class LDClient {
      - parameter useCache: How to handle flag caches during identify transition.
      - parameter completion: Closure called when the embedded `setOnlineIdentify` call completes, subject to throttling delays.
      */
-    public func identify(context: LDContext, useCache: IdentifyCacheUsage, completion: @escaping (_ result: IdentifyResult) -> Void) {
+    public func identify(context: LDContext, useCache: IdentifyCacheUsage, completion: @escaping @Sendable(_ result: IdentifyResult) -> Void) {
         _identify(context: context, sheddable: true, useCache: useCache, completion: completion)
     }
 
@@ -365,7 +365,7 @@ public class LDClient {
      - parameter timeout: The upper time limit before the `completion` callback will be invoked.
      - parameter completion: Closure called when the embedded `setOnlineIdentify` call completes, subject to throttling delays.
      */
-    public func identify(context: LDContext, timeout: TimeInterval, completion: @escaping ((_ result: IdentifyResult) -> Void)) {
+    public func identify(context: LDContext, timeout: TimeInterval, completion: @escaping (@Sendable (_ result: IdentifyResult) -> Void)) {
         identify(context: context, timeout: timeout, useCache: .yes, completion: completion)
     }
 
@@ -380,7 +380,7 @@ public class LDClient {
      - parameter useCache: How to handle flag caches during identify transition.
      - parameter completion: Closure called when the embedded `setOnlineIdentify` call completes, subject to throttling delays.
      */
-    public func identify(context: LDContext, timeout: TimeInterval, useCache: IdentifyCacheUsage, completion: @escaping ((_ result: IdentifyResult) -> Void)) {
+    public func identify(context: LDContext, timeout: TimeInterval, useCache: IdentifyCacheUsage, completion: @escaping (@Sendable (_ result: IdentifyResult) -> Void)) {
         if timeout > LDClient.longTimeoutInterval {
             os_log("%s LDClient.identify was called with a timeout greater than %f seconds. We recommend a timeout of less than %f seconds.", log: config.logger, type: .info, self.typeName(and: #function), LDClient.longTimeoutInterval, LDClient.longTimeoutInterval)
         }
@@ -495,7 +495,7 @@ public class LDClient {
 
      - parameter key: The LDFlagKey for the flag to observe.
      - parameter owner: The LDObserverOwner which will execute the handler. The SDK retains a weak reference to the owner.
-     - parameter handler: The closure the SDK will execute when the feature flag changes.
+     - parameter handler: The closure the SDK will execute when the feature flag changes. It executed on the main thread
     */
     public func observe(key: LDFlagKey, owner: LDObserverOwner, handler: @escaping LDFlagChangeHandler) {
         os_log("%s called for flagKey: %s", log: config.logger, type: .debug, typeName(and: #function), key)
@@ -523,7 +523,7 @@ public class LDClient {
 
      - parameter keys: An array of LDFlagKeys for the flags to observe.
      - parameter owner: The LDObserverOwner which will execute the handler. The SDK retains a weak reference to the owner.
-     - parameter handler: The LDFlagCollectionChangeHandler the SDK will execute 1 time when any of the observed feature flags change.
+     - parameter handler: The LDFlagCollectionChangeHandler the SDK will execute 1 time when any of the observed feature flags change. It executed on the main thread
      */
     public func observe(keys: [LDFlagKey], owner: LDObserverOwner, handler: @escaping LDFlagCollectionChangeHandler) {
         os_log("%s called for flagKeys: %s", log: config.logger, type: .debug, typeName(and: #function), String(describing: keys))
@@ -550,7 +550,7 @@ public class LDClient {
      ```
 
      - parameter owner: The LDObserverOwner which will execute the handler. The SDK retains a weak reference to the owner.
-     - parameter handler: The LDFlagCollectionChangeHandler the SDK will execute 1 time when any of the observed feature flags change.
+     - parameter handler: The LDFlagCollectionChangeHandler the SDK will execute 1 time when any of the observed feature flags change. It executed on the main thread
      */
     public func observeAll(owner: LDObserverOwner, handler: @escaping LDFlagCollectionChangeHandler) {
         os_log("%s called.", log: config.logger, type: .debug, typeName(and: #function))
@@ -577,7 +577,7 @@ public class LDClient {
      ```
 
      - parameter owner: The LDObserverOwner which will execute the handler. The SDK retains a weak reference to the owner.
-     - parameter handler: The LDFlagsUnchangedHandler the SDK will execute 1 time when a flag request completes with no flags changed.
+     - parameter handler: The LDFlagsUnchangedHandler the SDK will execute 1 time when a flag request completes with no flags changed. It executed on the main thread
      */
     public func observeFlagsUnchanged(owner: LDObserverOwner, handler: @escaping LDFlagsUnchangedHandler) {
         os_log("%s owner: %s", log: config.logger, type: .debug, typeName(and: #function), String(describing: owner))
@@ -601,7 +601,7 @@ public class LDClient {
      ```
 
      - parameter owner: The LDObserverOwner which will execute the handler. The SDK retains a weak reference to the owner.
-     - parameter handler: The LDConnectionModeChangedHandler the SDK will execute 1 time when ConnectionInformation.currentConnectionMode is changed.
+     - parameter handler: The LDConnectionModeChangedHandler the SDK will execute 1 time when ConnectionInformation.currentConnectionMode is changed. It executed on the main thread
      */
     public func observeCurrentConnectionMode(owner: LDObserverOwner, handler: @escaping LDConnectionModeChangedHandler) {
         os_log("%s owner: %s", log: config.logger, type: .debug, typeName(and: #function), String(describing: owner))
@@ -754,7 +754,7 @@ public class LDClient {
     */
     /// - Tag: start
     @available(*, deprecated, message: "Use LDClient.start(config: context: startWithSeconds: completion:) to initialize the SDK with a defined timeout")
-    public static func start(config: LDConfig, context: LDContext? = nil, completion: (() -> Void)? = nil) {
+    public static func start(config: LDConfig, context: LDContext? = nil, completion: (@Sendable() -> Void)? = nil) {
         start(serviceFactory: nil, config: config, context: context, completion: completion)
     }
 
@@ -845,7 +845,7 @@ public class LDClient {
     - parameter startWaitSeconds: A TimeInterval that determines when the completion will return if no flags have been returned from the network. If you use a large TimeInterval and wait for the timeout, then any network delays will cause your application to wait a long time before continuing execution.
     - parameter completion: Closure called when the embedded `setOnline` call completes. Takes a Bool that indicates whether the completion timedout as a parameter. (Optional)
     */
-    public static func start(config: LDConfig, context: LDContext? = nil, startWaitSeconds: TimeInterval, completion: ((_ timedOut: Bool) -> Void)? = nil) {
+    public static func start(config: LDConfig, context: LDContext? = nil, startWaitSeconds: TimeInterval, completion: (@Sendable(_ timedOut: Bool) -> Void)? = nil) {
         if startWaitSeconds > LDClient.longTimeoutInterval {
             os_log("%s LDClient.start was called with a timeout greater than %f seconds. We recommend a timeout of less than %f seconds.", log: config.logger, type: .info, self.typeName(and: #function), LDClient.longTimeoutInterval, LDClient.longTimeoutInterval)
         }
diff --git a/README.md b/README.md
index 6707c38d..c60438b6 100644
--- a/README.md
+++ b/README.md
@@ -88,6 +88,11 @@ If you prefer not to use the aforementioned dependency managers, it is possible
 4. Select the "General" tab, and if necessary expand the subsection "Frameworks, Libraries, and Embedded Content".
 5. Click the "+" button in the expanded subsection. Under "LaunchDarkly" within the dialog you will see 4 frameworks, select `LaunchDarkly.framework` for iOS, or `LaunchDarkly_<platform>` for other platforms.
 
+Note: To resolve Swift6 compilation issues use @preconcurrency attribure
+```
+@preconcurrency import LaunchDarkly
+```
+
 Learn more
 -----------