diff --git a/js-client-sdk-common.api.md b/js-client-sdk-common.api.md
index c10b46e9..31fa4466 100644
--- a/js-client-sdk-common.api.md
+++ b/js-client-sdk-common.api.md
@@ -25,7 +25,7 @@ export class EppoClient implements IEppoClient {
     // Warning: (ae-forgotten-export) The symbol "IConfigurationStore" needs to be exported by the entry point index.d.ts
     constructor(configurationStore: IConfigurationStore);
     // (undocumented)
-    getAssignment(subjectKey: string, experimentKey: string, subjectAttributes?: {}): string;
+    getAssignment(subjectKey: string, experimentKey: string, subjectAttributes?: {}): Promise<string>;
     // (undocumented)
     setLogger(logger: IAssignmentLogger): void;
 }
@@ -55,7 +55,7 @@ export interface IAssignmentLogger {
 
 // @public
 export interface IEppoClient {
-    getAssignment(subjectKey: string, experimentKey: string, subjectAttributes?: Record<string, any>): string;
+    getAssignment(subjectKey: string, experimentKey: string, subjectAttributes?: Record<string, any>): Promise<string>;
 }
 
 // @public (undocumented)
diff --git a/src/client/eppo-client.ts b/src/client/eppo-client.ts
index d83dbdf5..3b32cb2c 100644
--- a/src/client/eppo-client.ts
+++ b/src/client/eppo-client.ts
@@ -38,7 +38,11 @@ export default class EppoClient implements IEppoClient {
 
   constructor(private configurationStore: IConfigurationStore) {}
 
-  async getAssignment(subjectKey: string, experimentKey: string, subjectAttributes = {}): string {
+  async getAssignment(
+    subjectKey: string,
+    experimentKey: string,
+    subjectAttributes = {},
+  ): Promise<string> {
     validateNotBlank(subjectKey, 'Invalid argument: subjectKey cannot be blank');
     validateNotBlank(experimentKey, 'Invalid argument: experimentKey cannot be blank');