diff --git a/modules/openapi-generator/src/main/resources/typescript-angular/api.base.service.mustache b/modules/openapi-generator/src/main/resources/typescript-angular/api.base.service.mustache
index ed7a92be8bd2..1e47467264a8 100644
--- a/modules/openapi-generator/src/main/resources/typescript-angular/api.base.service.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript-angular/api.base.service.mustache
@@ -41,7 +41,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -69,8 +69,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -85,4 +85,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/typescript/typescriptangular/TypeScriptAngularClientCodegenTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/typescript/typescriptangular/TypeScriptAngularClientCodegenTest.java
index e3acfc556211..1d1aaeb6dd35 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/typescript/typescriptangular/TypeScriptAngularClientCodegenTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/typescript/typescriptangular/TypeScriptAngularClientCodegenTest.java
@@ -488,6 +488,10 @@ public void testDeepObject() throws IOException {
         final String fileContents = Files.readString(Paths.get(output + "/api/default.service.ts"));
         assertThat(fileContents).containsSubsequence("'options',\n", "<any>options,\n", "QueryParamStyle.DeepObject,\n", "true,\n");
         assertThat(fileContents).containsSubsequence("'inputOptions',\n", "<any>inputOptions,\n", "QueryParamStyle.DeepObject,\n", "true,\n");
+
+        final String baseServiceContents = Files.readString(Paths.get(output + "/api.base.service.ts"));
+        assertThat(baseServiceContents).contains("this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k])");
+        assertThat(baseServiceContents).contains("this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item)");
     }
 
     @Test
diff --git a/modules/openapi-generator/src/test/resources/integrationtests/typescript/additional-properties-expected/api.base.service.ts b/modules/openapi-generator/src/test/resources/integrationtests/typescript/additional-properties-expected/api.base.service.ts
index 7e447ce347e4..5c7a2d2f3fd8 100644
--- a/modules/openapi-generator/src/test/resources/integrationtests/typescript/additional-properties-expected/api.base.service.ts
+++ b/modules/openapi-generator/src/test/resources/integrationtests/typescript/additional-properties-expected/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -76,8 +76,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -92,4 +92,25 @@ export class BaseService {
             }
         }
     }
+    
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/modules/openapi-generator/src/test/resources/integrationtests/typescript/array-and-object-expected/api.base.service.ts b/modules/openapi-generator/src/test/resources/integrationtests/typescript/array-and-object-expected/api.base.service.ts
index 8868df446b43..d23e57dd76ad 100644
--- a/modules/openapi-generator/src/test/resources/integrationtests/typescript/array-and-object-expected/api.base.service.ts
+++ b/modules/openapi-generator/src/test/resources/integrationtests/typescript/array-and-object-expected/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -76,8 +76,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -92,4 +92,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/modules/openapi-generator/src/test/resources/integrationtests/typescript/custom-path-params-expected/api.base.service.ts b/modules/openapi-generator/src/test/resources/integrationtests/typescript/custom-path-params-expected/api.base.service.ts
index 7d64e8080b4b..0254fc849265 100644
--- a/modules/openapi-generator/src/test/resources/integrationtests/typescript/custom-path-params-expected/api.base.service.ts
+++ b/modules/openapi-generator/src/test/resources/integrationtests/typescript/custom-path-params-expected/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -76,8 +76,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -92,4 +92,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/modules/openapi-generator/src/test/resources/integrationtests/typescript/petstore-expected/api.base.service.ts b/modules/openapi-generator/src/test/resources/integrationtests/typescript/petstore-expected/api.base.service.ts
index 225e5863dcf2..197732757638 100644
--- a/modules/openapi-generator/src/test/resources/integrationtests/typescript/petstore-expected/api.base.service.ts
+++ b/modules/openapi-generator/src/test/resources/integrationtests/typescript/petstore-expected/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -76,8 +76,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -92,4 +92,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/others/typescript-angular-v20/builds/query-param-deep-object/api.base.service.ts b/samples/client/others/typescript-angular-v20/builds/query-param-deep-object/api.base.service.ts
index 1b63f4457d9c..80dad923cfd0 100644
--- a/samples/client/others/typescript-angular-v20/builds/query-param-deep-object/api.base.service.ts
+++ b/samples/client/others/typescript-angular-v20/builds/query-param-deep-object/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/others/typescript-angular-v20/builds/query-param-form/api.base.service.ts b/samples/client/others/typescript-angular-v20/builds/query-param-form/api.base.service.ts
index 7801405134b7..2112168a125a 100644
--- a/samples/client/others/typescript-angular-v20/builds/query-param-form/api.base.service.ts
+++ b/samples/client/others/typescript-angular-v20/builds/query-param-form/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/others/typescript-angular-v20/builds/query-param-json/api.base.service.ts b/samples/client/others/typescript-angular-v20/builds/query-param-json/api.base.service.ts
index 56df5e8f84b6..f50a0881a0fa 100644
--- a/samples/client/others/typescript-angular-v20/builds/query-param-json/api.base.service.ts
+++ b/samples/client/others/typescript-angular-v20/builds/query-param-json/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/others/typescript-angular/builds/composed-schemas-tagged-unions/api.base.service.ts b/samples/client/others/typescript-angular/builds/composed-schemas-tagged-unions/api.base.service.ts
index da9512f79726..5f25c2a67f46 100644
--- a/samples/client/others/typescript-angular/builds/composed-schemas-tagged-unions/api.base.service.ts
+++ b/samples/client/others/typescript-angular/builds/composed-schemas-tagged-unions/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/others/typescript-angular/builds/composed-schemas/api.base.service.ts b/samples/client/others/typescript-angular/builds/composed-schemas/api.base.service.ts
index da9512f79726..5f25c2a67f46 100644
--- a/samples/client/others/typescript-angular/builds/composed-schemas/api.base.service.ts
+++ b/samples/client/others/typescript-angular/builds/composed-schemas/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/petstore/typescript-angular-v16-provided-in-root/builds/default/api.base.service.ts b/samples/client/petstore/typescript-angular-v16-provided-in-root/builds/default/api.base.service.ts
index 8a8b8bc6b6f5..c68bef04a771 100644
--- a/samples/client/petstore/typescript-angular-v16-provided-in-root/builds/default/api.base.service.ts
+++ b/samples/client/petstore/typescript-angular-v16-provided-in-root/builds/default/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -78,7 +78,7 @@ export class BaseService {
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
                         Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, value[k], paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/petstore/typescript-angular-v17-provided-in-root/builds/default/api.base.service.ts b/samples/client/petstore/typescript-angular-v17-provided-in-root/builds/default/api.base.service.ts
index 8a8b8bc6b6f5..d0eadc84ae8e 100644
--- a/samples/client/petstore/typescript-angular-v17-provided-in-root/builds/default/api.base.service.ts
+++ b/samples/client/petstore/typescript-angular-v17-provided-in-root/builds/default/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/petstore/typescript-angular-v18-provided-in-root/builds/default/api.base.service.ts b/samples/client/petstore/typescript-angular-v18-provided-in-root/builds/default/api.base.service.ts
index 8a8b8bc6b6f5..d0eadc84ae8e 100644
--- a/samples/client/petstore/typescript-angular-v18-provided-in-root/builds/default/api.base.service.ts
+++ b/samples/client/petstore/typescript-angular-v18-provided-in-root/builds/default/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/petstore/typescript-angular-v19-provided-in-root/builds/default/api.base.service.ts b/samples/client/petstore/typescript-angular-v19-provided-in-root/builds/default/api.base.service.ts
index 8a8b8bc6b6f5..d0eadc84ae8e 100644
--- a/samples/client/petstore/typescript-angular-v19-provided-in-root/builds/default/api.base.service.ts
+++ b/samples/client/petstore/typescript-angular-v19-provided-in-root/builds/default/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/petstore/typescript-angular-v19-with-angular-dependency-params/builds/default/api.base.service.ts b/samples/client/petstore/typescript-angular-v19-with-angular-dependency-params/builds/default/api.base.service.ts
index 8a8b8bc6b6f5..d0eadc84ae8e 100644
--- a/samples/client/petstore/typescript-angular-v19-with-angular-dependency-params/builds/default/api.base.service.ts
+++ b/samples/client/petstore/typescript-angular-v19-with-angular-dependency-params/builds/default/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/petstore/typescript-angular-v19/builds/default/api.base.service.ts b/samples/client/petstore/typescript-angular-v19/builds/default/api.base.service.ts
index 8a8b8bc6b6f5..d0eadc84ae8e 100644
--- a/samples/client/petstore/typescript-angular-v19/builds/default/api.base.service.ts
+++ b/samples/client/petstore/typescript-angular-v19/builds/default/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/petstore/typescript-angular-v20-provided-in-root/builds/default/api.base.service.ts b/samples/client/petstore/typescript-angular-v20-provided-in-root/builds/default/api.base.service.ts
index 8a8b8bc6b6f5..d0eadc84ae8e 100644
--- a/samples/client/petstore/typescript-angular-v20-provided-in-root/builds/default/api.base.service.ts
+++ b/samples/client/petstore/typescript-angular-v20-provided-in-root/builds/default/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/petstore/typescript-angular-v20/builds/default/api.base.service.ts b/samples/client/petstore/typescript-angular-v20/builds/default/api.base.service.ts
index 8a8b8bc6b6f5..d0eadc84ae8e 100644
--- a/samples/client/petstore/typescript-angular-v20/builds/default/api.base.service.ts
+++ b/samples/client/petstore/typescript-angular-v20/builds/default/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/petstore/typescript-angular-v21-provided-in-root/builds/default/api.base.service.ts b/samples/client/petstore/typescript-angular-v21-provided-in-root/builds/default/api.base.service.ts
index 8a8b8bc6b6f5..d0eadc84ae8e 100644
--- a/samples/client/petstore/typescript-angular-v21-provided-in-root/builds/default/api.base.service.ts
+++ b/samples/client/petstore/typescript-angular-v21-provided-in-root/builds/default/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }
diff --git a/samples/client/petstore/typescript-angular-v21/builds/default/api.base.service.ts b/samples/client/petstore/typescript-angular-v21/builds/default/api.base.service.ts
index 8a8b8bc6b6f5..d0eadc84ae8e 100644
--- a/samples/client/petstore/typescript-angular-v21/builds/default/api.base.service.ts
+++ b/samples/client/petstore/typescript-angular-v21/builds/default/api.base.service.ts
@@ -49,7 +49,7 @@ export class BaseService {
             }
 
             return Object.keys(value as Record<string, any>).reduce(
-                (hp, k) => hp.append(`${key}[${k}]`, value[k]),
+                (hp, k) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, value[k]),
                 httpParams,
             );
         } else if (paramStyle === QueryParamStyle.Json) {
@@ -77,8 +77,8 @@ export class BaseService {
                 // Otherwise, if it's an object, add each field.
                 if (paramStyle === QueryParamStyle.Form) {
                     if (explode) {
-                        Object.keys(value).forEach(k => {
-                            httpParams = this.addToHttpParams(httpParams, k, value[k], paramStyle, explode);
+                        Object.entries(value).forEach(([k, v]) => {
+                            httpParams = this.addToHttpParams(httpParams, `${key}.${k}`, v, paramStyle, explode);
                         });
                         return httpParams;
                     } else {
@@ -93,4 +93,25 @@ export class BaseService {
             }
         }
     }
+
+    private addToHttpParamsDeepObject(httpParams: OpenApiHttpParams, key: string, value: any | null | undefined): OpenApiHttpParams {
+        if (value == null) {
+            return httpParams;
+        } else if (value instanceof Date) {
+            return httpParams.append(key, value.toISOString());
+        } else if (Object(value) !== value) {
+            return httpParams.append(key, value.toString());
+        } else if (Array.isArray(value) || value instanceof Set) {
+            const array = Array.isArray(value) ? value : Array.from(value);
+            array.forEach((item, index) => {
+                httpParams = this.addToHttpParamsDeepObject(httpParams, `${key}[${index}]`, item);
+            });
+            return httpParams;
+        } else {
+            return Object.entries(value).reduce(
+                (hp, [k, v]) => this.addToHttpParamsDeepObject(hp, `${key}[${k}]`, v),
+                httpParams,
+            );
+        }
+    }
 }