diff --git a/.changeset/soft-falcons-summarize.md b/.changeset/soft-falcons-summarize.md
new file mode 100644
index 000000000..397933eea
--- /dev/null
+++ b/.changeset/soft-falcons-summarize.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/ai': patch
+---
+
+Fix provider-specific model options inference for TTS, transcription, and summarize activities.
diff --git a/packages/ai/src/activities/generateSpeech/index.ts b/packages/ai/src/activities/generateSpeech/index.ts
index 9a96d8221..70a5053f6 100644
--- a/packages/ai/src/activities/generateSpeech/index.ts
+++ b/packages/ai/src/activities/generateSpeech/index.ts
@@ -43,10 +43,11 @@ export const kind = 'tts' as const
 /**
  * Extract provider options from a TTSAdapter via ~types.
  */
-export type TTSProviderOptions<TAdapter> =
-  TAdapter extends TTSAdapter<any, any>
-    ? TAdapter['~types']['providerOptions']
-    : object
+export type TTSProviderOptions<TAdapter> = TAdapter extends {
+  '~types': { providerOptions: infer P extends object }
+}
+  ? P
+  : object
 
 // ===========================
 // Activity Options Type
diff --git a/packages/ai/src/activities/generateTranscription/index.ts b/packages/ai/src/activities/generateTranscription/index.ts
index 96d85f2e5..c658b2f6b 100644
--- a/packages/ai/src/activities/generateTranscription/index.ts
+++ b/packages/ai/src/activities/generateTranscription/index.ts
@@ -47,10 +47,11 @@ export const kind = 'transcription' as const
 /**
  * Extract provider options from a TranscriptionAdapter via ~types.
  */
-export type TranscriptionProviderOptions<TAdapter> =
-  TAdapter extends TranscriptionAdapter<any, any>
-    ? TAdapter['~types']['providerOptions']
-    : object
+export type TranscriptionProviderOptions<TAdapter> = TAdapter extends {
+  '~types': { providerOptions: infer P extends object }
+}
+  ? P
+  : object
 
 // ===========================
 // Activity Options Type
diff --git a/packages/ai/src/activities/summarize/index.ts b/packages/ai/src/activities/summarize/index.ts
index f890844b0..c1d7e5262 100644
--- a/packages/ai/src/activities/summarize/index.ts
+++ b/packages/ai/src/activities/summarize/index.ts
@@ -41,10 +41,11 @@ export const kind = 'summarize' as const
 // ===========================
 
 /** Extract provider options from a SummarizeAdapter via ~types */
-export type SummarizeProviderOptions<TAdapter> =
-  TAdapter extends SummarizeAdapter<any, any>
-    ? TAdapter['~types']['providerOptions']
-    : object
+export type SummarizeProviderOptions<TAdapter> = TAdapter extends {
+  '~types': { providerOptions: infer P extends object }
+}
+  ? P
+  : object
 
 // ===========================
 // Activity Options Type
@@ -213,18 +214,12 @@ export function summarize<
 
   if (stream) {
     return runStreamingSummarize(
-      options as SummarizeActivityOptions<
-        SummarizeAdapter<string, object>,
-        true
-      >,
+      options as SummarizeActivityOptions<TAdapter, true>,
     ) as SummarizeActivityResult<TStream>
   }
 
   return runSummarize(
-    options as SummarizeActivityOptions<
-      SummarizeAdapter<string, object>,
-      false
-    >,
+    options as SummarizeActivityOptions<TAdapter, false>,
   ) as SummarizeActivityResult<TStream>
 }