diff --git a/.changeset/cruel-horses-cheat.md b/.changeset/cruel-horses-cheat.md
new file mode 100644
index 000000000000..06db91308f3c
--- /dev/null
+++ b/.changeset/cruel-horses-cheat.md
@@ -0,0 +1,10 @@
+---
+"@fluidframework/container-runtime": minor
+---
+---
+"section": legacy
+---
+
+IContainerRuntimeOptions.flushMode has been removed
+
+See [2.12.0 release note](https://github.com/microsoft/FluidFramework/releases/tag/client_v2.12.0#user-content-icontainerruntimeoptionsflushmode-is-now-deprecated-23288)
diff --git a/packages/runtime/container-runtime/api-report/container-runtime.legacy.alpha.api.md b/packages/runtime/container-runtime/api-report/container-runtime.legacy.alpha.api.md
index b7faa6065487..90264330f335 100644
--- a/packages/runtime/container-runtime/api-report/container-runtime.legacy.alpha.api.md
+++ b/packages/runtime/container-runtime/api-report/container-runtime.legacy.alpha.api.md
@@ -34,7 +34,7 @@ export enum ContainerMessageType {
 
 // @alpha @deprecated
 export class ContainerRuntime extends TypedEventEmitter<IContainerRuntimeEvents> implements IContainerRuntime, IRuntime, ISummarizerRuntime, ISummarizerInternalsProvider, IProvideFluidHandleContext {
-    protected constructor(context: IContainerContext, registry: IFluidDataStoreRegistry, metadata: IContainerRuntimeMetadata | undefined, electedSummarizerData: ISerializedElection | undefined, chunks: [string, string[]][], dataStoreAliasMap: [string, string][], runtimeOptions: Readonly<Required<Omit<IContainerRuntimeOptions, "flushMode" | "enableGroupedBatching">> & IContainerRuntimeOptions>, containerScope: FluidObject, baseLogger: ITelemetryBaseLogger, existing: boolean, blobManagerSnapshot: IBlobManagerLoadInfo, _storage: IDocumentStorageService, createIdCompressor: () => Promise<IIdCompressor & IIdCompressorCore>, documentsSchemaController: DocumentsSchemaController, featureGatesForTelemetry: Record<string, boolean | number | undefined>, provideEntryPoint: (containerRuntime: IContainerRuntime) => Promise<FluidObject>, requestHandler?: ((request: IRequest, runtime: IContainerRuntime) => Promise<IResponse>) | undefined, summaryConfiguration?: ISummaryConfiguration, recentBatchInfo?: [number, string][]);
+    protected constructor(context: IContainerContext, registry: IFluidDataStoreRegistry, metadata: IContainerRuntimeMetadata | undefined, electedSummarizerData: ISerializedElection | undefined, chunks: [string, string[]][], dataStoreAliasMap: [string, string][], runtimeOptions: Readonly<Required<IContainerRuntimeOptions>>, containerScope: FluidObject, baseLogger: ITelemetryBaseLogger, existing: boolean, blobManagerSnapshot: IBlobManagerLoadInfo, _storage: IDocumentStorageService, createIdCompressor: () => Promise<IIdCompressor & IIdCompressorCore>, documentsSchemaController: DocumentsSchemaController, featureGatesForTelemetry: Record<string, boolean | number | undefined>, provideEntryPoint: (containerRuntime: IContainerRuntime) => Promise<FluidObject>, requestHandler?: ((request: IRequest, runtime: IContainerRuntime) => Promise<IResponse>) | undefined, summaryConfiguration?: ISummaryConfiguration, recentBatchInfo?: [number, string][]);
     // (undocumented)
     protected addContainerStateToSummary(summaryTree: ISummaryTreeWithStats, fullTree: boolean, trackState: boolean, telemetryContext?: ITelemetryContext): void;
     addedGCOutboundRoute(fromPath: string, toPath: string, messageTimestampMs?: number): void;
@@ -342,8 +342,6 @@ export interface IContainerRuntimeOptions {
     readonly compressionOptions?: ICompressionRuntimeOptions;
     readonly enableRuntimeIdCompressor?: IdCompressorMode;
     readonly explicitSchemaControl?: boolean;
-    // @deprecated
-    readonly flushMode?: FlushMode;
     // (undocumented)
     readonly gcOptions?: IGCRuntimeOptions;
     readonly loadSequenceNumberVerification?: "close" | "log" | "bypass";
diff --git a/packages/runtime/container-runtime/src/containerRuntime.ts b/packages/runtime/container-runtime/src/containerRuntime.ts
index d9b3a9822b97..f19e966fbb18 100644
--- a/packages/runtime/container-runtime/src/containerRuntime.ts
+++ b/packages/runtime/container-runtime/src/containerRuntime.ts
@@ -470,15 +470,7 @@ export interface IContainerRuntimeOptions {
 	 * 3. "bypass" will skip the check entirely. This is not recommended.
 	 */
 	readonly loadSequenceNumberVerification?: "close" | "log" | "bypass";
-	/**
-	 * Sets the flush mode for the runtime. In Immediate flush mode the runtime will immediately
-	 * send all operations to the driver layer, while in TurnBased the operations will be buffered
-	 * and then sent them as a single batch at the end of the turn.
-	 * By default, flush mode is TurnBased.
-	 *
-	 * @deprecated Only the default value TurnBased is supported. This option will be removed in the future.
-	 */
-	readonly flushMode?: FlushMode;
+
 	/**
 	 * Enables the runtime to compress ops. See {@link ICompressionRuntimeOptions}.
 	 */
@@ -1512,10 +1504,7 @@ export class ContainerRuntime
 		electedSummarizerData: ISerializedElection | undefined,
 		chunks: [string, string[]][],
 		dataStoreAliasMap: [string, string][],
-		runtimeOptions: Readonly<
-			Required<Omit<IContainerRuntimeOptions, "flushMode" | "enableGroupedBatching">> &
-				IContainerRuntimeOptions // Let flushMode and enabledGroupedBatching be optional now since they're soon to be removed
-		>,
+		runtimeOptions: Readonly<Required<IContainerRuntimeOptions>>,
 		private readonly containerScope: FluidObject,
 		// Create a custom ITelemetryBaseLogger to output telemetry events.
 		public readonly baseLogger: ITelemetryBaseLogger,