diff --git a/apps/client/public/locales/en-US/translation.json b/apps/client/public/locales/en-US/translation.json
index 8cfd742c..87e8af42 100644
--- a/apps/client/public/locales/en-US/translation.json
+++ b/apps/client/public/locales/en-US/translation.json
@@ -1191,5 +1191,9 @@
   "Transcription failed": "Transcription failed",
   "Voice dictation is not configured": "Voice dictation is not configured",
   "Microphone is unavailable or already in use": "Microphone is unavailable or already in use",
-  "Audio recording is not available in this browser/context": "Audio recording is not available in this browser/context"
+  "Audio recording is not available in this browser/context": "Audio recording is not available in this browser/context",
+  "Request format": "Request format",
+  "How transcription requests are sent to the endpoint": "How transcription requests are sent to the endpoint",
+  "OpenAI-compatible (multipart/form-data)": "OpenAI-compatible (multipart/form-data)",
+  "OpenRouter (JSON, base64 audio)": "OpenRouter (JSON, base64 audio)"
 }
diff --git a/apps/client/src/features/workspace/components/settings/components/ai-provider-settings.tsx b/apps/client/src/features/workspace/components/settings/components/ai-provider-settings.tsx
index b908fc03..78727bda 100644
--- a/apps/client/src/features/workspace/components/settings/components/ai-provider-settings.tsx
+++ b/apps/client/src/features/workspace/components/settings/components/ai-provider-settings.tsx
@@ -9,6 +9,7 @@ import {
   Modal,
   Paper,
   PasswordInput,
+  Select,
   Stack,
   Switch,
   Text,
@@ -32,7 +33,10 @@ import {
   useTestAiConnectionMutation,
   useUpdateAiSettingsMutation,
 } from "@/features/workspace/queries/ai-settings-query.ts";
-import { IAiSettingsUpdate } from "@/features/workspace/services/ai-settings-service.ts";
+import {
+  IAiSettingsUpdate,
+  SttApiStyle,
+} from "@/features/workspace/services/ai-settings-service.ts";
 import AiMcpServers from "./ai-mcp-servers.tsx";
 
 // No driver field: every endpoint is OpenAI-compatible, so the form carries only
@@ -50,6 +54,7 @@ const formSchema = z.object({
   // STT-specific fields. Empty base URL / key fall back to the chat ones.
   sttModel: z.string(),
   sttBaseUrl: z.string(),
+  sttApiStyle: z.enum(["multipart", "json"]),
   sttApiKey: z.string(),
 });
 
@@ -139,6 +144,7 @@ export default function AiProviderSettings() {
       embeddingApiKey: "",
       sttModel: "",
       sttBaseUrl: "",
+      sttApiStyle: "multipart" as SttApiStyle,
       sttApiKey: "",
     },
   });
@@ -157,6 +163,7 @@ export default function AiProviderSettings() {
       embeddingApiKey: "",
       sttModel: settings.sttModel ?? "",
       sttBaseUrl: settings.sttBaseUrl ?? "",
+      sttApiStyle: settings.sttApiStyle ?? "multipart",
       sttApiKey: "",
     });
     form.resetDirty();
@@ -184,6 +191,7 @@ export default function AiProviderSettings() {
       // server-side.
       sttModel: values.sttModel,
       sttBaseUrl: values.sttBaseUrl,
+      sttApiStyle: values.sttApiStyle,
     };
 
     // Key semantics (never send the stored key back):
@@ -671,6 +679,22 @@ export default function AiProviderSettings() {
           </Stack>
         </Group>
 
+        <Select
+          mt="sm"
+          label={t("Request format")}
+          description={t("How transcription requests are sent to the endpoint")}
+          data={[
+            {
+              value: "multipart",
+              label: t("OpenAI-compatible (multipart/form-data)"),
+            },
+            { value: "json", label: t("OpenRouter (JSON, base64 audio)") },
+          ]}
+          allowDeselect={false}
+          disabled={isLoading}
+          {...form.getInputProps("sttApiStyle")}
+        />
+
         <TextInput
           mt="sm"
           label={t("Base URL")}
diff --git a/apps/client/src/features/workspace/services/ai-settings-service.ts b/apps/client/src/features/workspace/services/ai-settings-service.ts
index 99490189..ef939ff1 100644
--- a/apps/client/src/features/workspace/services/ai-settings-service.ts
+++ b/apps/client/src/features/workspace/services/ai-settings-service.ts
@@ -3,6 +3,12 @@ import api from "@/lib/api-client";
 // Supported LLM providers/drivers.
 export type AiDriver = "openai" | "gemini" | "ollama";
 
+// How STT (speech-to-text) requests are encoded for the transcription endpoint.
+//   - 'multipart' -> OpenAI-compatible multipart/form-data (OpenAI, speaches,
+//     faster-whisper-server)
+//   - 'json'      -> JSON body with base64-encoded audio (OpenRouter)
+export type SttApiStyle = "multipart" | "json";
+
 // Masked AI provider settings returned by the server.
 // No API key is ever returned; only `hasApiKey` / `hasEmbeddingApiKey` indicate
 // whether one is stored. `embeddingBaseUrl` is the RAW stored value (empty means
@@ -21,6 +27,7 @@ export interface IAiSettings {
   // key is stored (empty means "uses the chat API key").
   sttModel?: string;
   sttBaseUrl?: string;
+  sttApiStyle?: SttApiStyle;
   hasSttApiKey: boolean;
   // RAG indexing coverage (pages indexed for semantic search).
   indexedPages: number;
@@ -43,6 +50,7 @@ export interface IAiSettingsUpdate {
   embeddingApiKey?: string;
   sttModel?: string;
   sttBaseUrl?: string;
+  sttApiStyle?: SttApiStyle;
   // Write-only STT key (same semantics as `apiKey` / `embeddingApiKey`).
   sttApiKey?: string;
 }
diff --git a/apps/server/src/database/repos/workspace/workspace.repo.ts b/apps/server/src/database/repos/workspace/workspace.repo.ts
index 2f8e1b08..b5d62f7a 100644
--- a/apps/server/src/database/repos/workspace/workspace.repo.ts
+++ b/apps/server/src/database/repos/workspace/workspace.repo.ts
@@ -239,7 +239,7 @@ export class WorkspaceRepo {
     // is a real jsonb object, never a double-encoded string. The CASE self-heals
     // workspaces whose settings.ai.provider was previously corrupted into an
     // array/string.
-    const ALLOWED = ['driver', 'chatModel', 'embeddingModel', 'baseUrl', 'embeddingBaseUrl', 'sttModel', 'sttBaseUrl', 'systemPrompt'];
+    const ALLOWED = ['driver', 'chatModel', 'embeddingModel', 'baseUrl', 'embeddingBaseUrl', 'sttModel', 'sttBaseUrl', 'sttApiStyle', 'systemPrompt'];
     const entries = Object.entries(provider).filter(
       ([k, v]) => v !== undefined && ALLOWED.includes(k),
     );
diff --git a/apps/server/src/integrations/ai/ai-settings.service.ts b/apps/server/src/integrations/ai/ai-settings.service.ts
index 315ff380..f8fb6996 100644
--- a/apps/server/src/integrations/ai/ai-settings.service.ts
+++ b/apps/server/src/integrations/ai/ai-settings.service.ts
@@ -12,6 +12,7 @@ import {
   AiProviderSettings,
   MaskedAiSettings,
   ResolvedAiConfig,
+  SttApiStyle,
 } from './ai.types';
 
 /**
@@ -30,6 +31,7 @@ export interface UpdateAiSettingsInput {
   embeddingApiKey?: string;
   sttModel?: string;
   sttBaseUrl?: string;
+  sttApiStyle?: SttApiStyle;
   sttApiKey?: string;
 }
 
@@ -117,6 +119,9 @@ export class AiSettingsService {
       chatModel: provider.chatModel,
       embeddingModel: provider.embeddingModel,
       sttModel: provider.sttModel,
+      // Plain passthrough, no fallback; the transcribe path defaults unset to
+      // 'multipart' (current behavior).
+      sttApiStyle: provider.sttApiStyle,
       baseUrl: provider.baseUrl,
       systemPrompt: provider.systemPrompt,
     };
@@ -190,6 +195,7 @@ export class AiSettingsService {
       embeddingBaseUrl: provider.embeddingBaseUrl,
       sttModel: provider.sttModel,
       sttBaseUrl: provider.sttBaseUrl,
+      sttApiStyle: provider.sttApiStyle,
       systemPrompt: provider.systemPrompt,
       hasApiKey,
       hasEmbeddingApiKey,
@@ -226,6 +232,7 @@ export class AiSettingsService {
       'embeddingBaseUrl',
       'sttModel',
       'sttBaseUrl',
+      'sttApiStyle',
       'systemPrompt',
     ] as const) {
       if (nonSecret[key] !== undefined) {
diff --git a/apps/server/src/integrations/ai/ai.service.ts b/apps/server/src/integrations/ai/ai.service.ts
index e894d703..fef30a5b 100644
--- a/apps/server/src/integrations/ai/ai.service.ts
+++ b/apps/server/src/integrations/ai/ai.service.ts
@@ -1,4 +1,4 @@
-import { Injectable, Logger } from '@nestjs/common';
+import { BadRequestException, Injectable, Logger } from '@nestjs/common';
 import {
   embedMany,
   experimental_transcribe as transcribe,
@@ -108,28 +108,14 @@ export class AiService {
     }
   }
 
-  // Some OpenAI-compatible gateways diverge on the transcription API. OpenRouter
-  // does NOT accept OpenAI's multipart /audio/transcriptions; it wants JSON
-  // { model, input_audio: { data: <base64>, format } }. Detect it by host so the
-  // standard multipart path (OpenAI, speaches, faster-whisper-server, ...) is
-  // unaffected.
-  private static isOpenRouter(baseURL?: string): boolean {
-    if (!baseURL) return false;
-    try {
-      const host = new URL(baseURL).hostname.toLowerCase();
-      // Exact host or a real subdomain — avoid matching e.g. "evil-openrouter.ai".
-      return host === 'openrouter.ai' || host.endsWith('.openrouter.ai');
-    } catch {
-      return false;
-    }
-  }
-
   /**
-   * Transcribe audio with the workspace STT model. Standard OpenAI-compatible
-   * endpoints use the AI SDK multipart path; OpenRouter uses its JSON+base64
-   * audio/transcriptions API. `format` is the audio container hint (webm / mp4 /
-   * wav / mp3 / ogg / m4a). Built PER WORKSPACE; the key is never logged. Throws
-   * AiSttNotConfiguredException (-> 503) when no STT model is configured.
+   * Transcribe audio with the workspace STT model. The request encoding is the
+   * admin-chosen `sttApiStyle`: 'json' uses the JSON+base64 audio/transcriptions
+   * API (OpenRouter); anything else (default 'multipart') uses the AI SDK
+   * multipart path (OpenAI, speaches, faster-whisper-server, ...). `format` is
+   * the audio container hint (webm / mp4 / wav / mp3 / ogg / m4a). Built PER
+   * WORKSPACE; the key is never logged. Throws AiSttNotConfiguredException
+   * (-> 503) when no STT model is configured.
    */
   async transcribe(
     workspaceId: string,
@@ -140,14 +126,11 @@ export class AiService {
     if (!cfg?.sttModel) throw new AiSttNotConfiguredException();
     const baseURL = cfg.sttBaseUrl || cfg.baseUrl;
 
-    if (AiService.isOpenRouter(baseURL)) {
-      return this.transcribeViaOpenRouter(
-        baseURL as string,
-        cfg.sttApiKey,
-        cfg.sttModel,
-        audio,
-        format,
-      );
+    // Explicit, admin-chosen request encoding (no URL guessing). 'json' is the
+    // OpenRouter style (JSON + base64 input_audio); everything else uses the
+    // OpenAI-compatible multipart path via the AI SDK.
+    if (cfg.sttApiStyle === 'json') {
+      return this.transcribeJsonBase64(baseURL, cfg.sttApiKey, cfg.sttModel, audio, format);
     }
 
     // Standard OpenAI-compatible multipart path (AI SDK). apiKey may be unused for
@@ -160,14 +143,23 @@ export class AiService {
     return text.trim();
   }
 
-  // OpenRouter transcription: JSON body with base64 audio; returns { text }.
-  private async transcribeViaOpenRouter(
-    baseURL: string,
+  /**
+   * JSON + base64 transcription body (OpenRouter-style). POSTs
+   * { model, input_audio: { data, format } } to {baseURL}/audio/transcriptions
+   * and returns { text }.
+   */
+  private async transcribeJsonBase64(
+    baseURL: string | undefined,
     apiKey: string | undefined,
     model: string,
     audio: Uint8Array,
     format: string,
   ): Promise<string> {
+    if (!baseURL) {
+      throw new BadRequestException(
+        'STT base URL is not set (required for the JSON request format)',
+      );
+    }
     const url = `${baseURL.replace(/\/$/, '')}/audio/transcriptions`;
     const res = await fetch(url, {
       method: 'POST',
@@ -187,7 +179,7 @@ export class AiService {
       // Surface status + body so the real reason reaches the user; never log the key.
       const body = await res.text().catch(() => '');
       throw new Error(
-        `OpenRouter transcription failed (${res.status}): ${body.slice(0, 500)}`,
+        `JSON transcription request failed (${res.status}): ${body.slice(0, 500)}`,
       );
     }
     const json = (await res.json()) as { text?: string };
diff --git a/apps/server/src/integrations/ai/ai.types.ts b/apps/server/src/integrations/ai/ai.types.ts
index 32f043c8..4f4258ad 100644
--- a/apps/server/src/integrations/ai/ai.types.ts
+++ b/apps/server/src/integrations/ai/ai.types.ts
@@ -10,6 +10,12 @@ export type AiDriver = 'openai' | 'gemini' | 'ollama';
 
 export const AI_DRIVERS: AiDriver[] = ['openai', 'gemini', 'ollama'];
 
+// STT request encoding. 'multipart' = OpenAI-compatible /audio/transcriptions
+// form-data (OpenAI, speaches, faster-whisper-server). 'json' = JSON body with
+// base64 input_audio (OpenRouter). Chosen explicitly by the admin.
+export type SttApiStyle = 'multipart' | 'json';
+export const STT_API_STYLES: SttApiStyle[] = ['multipart', 'json'];
+
 /**
  * Non-secret provider settings persisted under `settings.ai.provider`.
  * The API key is intentionally absent here.
@@ -24,6 +30,7 @@ export interface AiProviderSettings {
   sttModel?: string;
   // STT-specific base URL. Falls back to baseUrl when empty/unset.
   sttBaseUrl?: string;
+  sttApiStyle?: SttApiStyle;
   systemPrompt?: string;
 }
 
@@ -58,6 +65,7 @@ export interface MaskedAiSettings {
   embeddingBaseUrl?: string;
   sttModel?: string;
   sttBaseUrl?: string;
+  sttApiStyle?: SttApiStyle;
   systemPrompt?: string;
   hasApiKey: boolean;
   hasEmbeddingApiKey: boolean;
diff --git a/apps/server/src/integrations/ai/dto/update-ai-settings.dto.ts b/apps/server/src/integrations/ai/dto/update-ai-settings.dto.ts
index 49199bc0..77935352 100644
--- a/apps/server/src/integrations/ai/dto/update-ai-settings.dto.ts
+++ b/apps/server/src/integrations/ai/dto/update-ai-settings.dto.ts
@@ -1,5 +1,5 @@
 import { IsIn, IsOptional, IsString } from 'class-validator';
-import { AI_DRIVERS, AiDriver } from '../ai.types';
+import { AI_DRIVERS, AiDriver, STT_API_STYLES, SttApiStyle } from '../ai.types';
 
 /**
  * Admin update payload for the workspace AI provider settings.
@@ -50,6 +50,10 @@ export class UpdateAiSettingsDto {
   @IsString()
   sttBaseUrl?: string;
 
+  @IsOptional()
+  @IsIn(STT_API_STYLES)
+  sttApiStyle?: SttApiStyle;
+
   @IsOptional()
   @IsString()
   sttApiKey?: string;