diff --git a/packages/ai/src/protocols/deepgram-speech.ts b/packages/ai/src/protocols/deepgram-speech.ts
index 59b58db1d41..b8d3390fc72 100644
--- a/packages/ai/src/protocols/deepgram-speech.ts
+++ b/packages/ai/src/protocols/deepgram-speech.ts
@@ -67,6 +67,9 @@ const queryParameters = (request: Request) => {
 }
 
 const fromRequest = Effect.fn("DeepgramSpeech.fromRequest")(function* (request: Request) {
+  // Not in `unsupported`: that list would also reject `timestamps: false`, which asks for nothing.
+  if (request.timestamps === true)
+    return yield* route.unsupported("media.timestamps", `${route.name} does not return timestamps`)
   if (
     request.format !== undefined &&
     FORMATS[request.format] === undefined &&
@@ -117,7 +120,7 @@ const finish = (state: State, context: MediaProtocol.ResponseContext<Request>) =
 // ---------------------------------------------------------------------------
 
 export const protocol = MediaProtocol.stream<Request, SpeechEvent, Uint8Array, State>(route, {
-  unsupported: ["voice", "language", "instructions", "timestamps"],
+  unsupported: ["voice", "language", "instructions"],
   body: { from: fromRequest },
   frames: (bytes) => bytes,
   initial: () => ({ chunks: [] }),
diff --git a/packages/ai/src/protocols/google-speech.ts b/packages/ai/src/protocols/google-speech.ts
index f168f416b56..02534d3ca76 100644
--- a/packages/ai/src/protocols/google-speech.ts
+++ b/packages/ai/src/protocols/google-speech.ts
@@ -56,6 +56,9 @@ interface State extends SpeechStream.Audio, GeminiGenerateContent.Metadata {
 // ---------------------------------------------------------------------------
 
 const fromRequest = Effect.fn("GoogleSpeech.fromRequest")(function* (request: MediaProtocol.Addressed<Request>) {
+  // Not in `unsupported`: that list would also reject `timestamps: false`, which asks for nothing.
+  if (request.timestamps === true)
+    return yield* route.unsupported("media.timestamps", `${route.name} does not return timestamps`)
   if (request.format === "pcm" && request.mode === "generate" && /^gemini-3\.8-.*-tts(?:-|$)/.test(request.model.id))
     return yield* route.unsupported(
       "media.format",
@@ -125,7 +128,7 @@ const finish = (state: State, context: MediaProtocol.ResponseContext<Request>) =
 // ---------------------------------------------------------------------------
 
 export const protocol = MediaProtocol.stream<Request, SpeechEvent, string, State>(route, {
-  unsupported: ["instructions", "speed", "timestamps"],
+  unsupported: ["instructions", "speed"],
   body: { from: fromRequest },
   frames: (bytes, context) => GeminiGenerateContent.frames(bytes, context.request.mode),
   initial: () => ({ chunks: [] }),
diff --git a/packages/ai/src/protocols/openai-speech.ts b/packages/ai/src/protocols/openai-speech.ts
index 7fc12dc5a0a..50ea4cbd21b 100644
--- a/packages/ai/src/protocols/openai-speech.ts
+++ b/packages/ai/src/protocols/openai-speech.ts
@@ -61,6 +61,9 @@ interface State extends SpeechStream.Audio {
 const supportsSse = (model: string) => !/^tts-1(-hd)?(-|$)/.test(model)
 
 const fromRequest = Effect.fn("OpenAISpeech.fromRequest")(function* (request: MediaProtocol.Addressed<Request>) {
+  // Not in `unsupported`: that list would also reject `timestamps: false`, which asks for nothing.
+  if (request.timestamps === true)
+    return yield* route.unsupported("media.timestamps", `${route.name} does not return timestamps`)
   return MediaProtocol.json(
     mergeJsonRecords(
       {
@@ -121,7 +124,7 @@ const finish = (state: State, context: MediaProtocol.ResponseContext<Request>) =
 // ---------------------------------------------------------------------------
 
 export const protocol = MediaProtocol.stream<Request, SpeechEvent, string | Uint8Array, State>(route, {
-  unsupported: ["language", "timestamps"],
+  unsupported: ["language"],
   body: { from: fromRequest },
   frames: (bytes, context) => (isSse(context.body) ? Framing.sse.frame(bytes) : bytes),
   initial: () => ({ chunks: [], done: false }),
diff --git a/packages/ai/src/route/media.ts b/packages/ai/src/route/media.ts
index b3c278b121b..0dca4ac69a2 100644
--- a/packages/ai/src/route/media.ts
+++ b/packages/ai/src/route/media.ts
@@ -385,7 +385,11 @@ const encode = (body: MediaProtocol.Body | undefined, headers: Headers.Headers)
   }
 }
 
-/** Common fields are never silently dropped: a present field the protocol declared unsupported fails typed. */
+/**
+ * Common fields are never silently dropped: a present field the protocol declared unsupported fails typed. `false`
+ * counts as present because some booleans mean something when false (video `audio`); protocols reject opt-in
+ * booleans such as speech `timestamps` with `=== true` in `body.from` instead of listing them.
+ */
 const rejectUnsupported = <Request extends object>(
   route: string,
   provider: ProviderID,
diff --git a/packages/ai/test/speech.test.ts b/packages/ai/test/speech.test.ts
index a4ae078ed32..d5731b97a95 100644
--- a/packages/ai/test/speech.test.ts
+++ b/packages/ai/test/speech.test.ts
@@ -97,6 +97,42 @@ describe("Speech", () => {
     }).pipe(Effect.provide(layer(() => Effect.die("an unsupported request reached the network")))),
   )
 
+  it.effect("treats timestamps: false as not asking for timestamps on routes that cannot return them", () =>
+    Effect.gen(function* () {
+      const bytes = Uint8Array.from([1, 2, 3])
+      const gemini = JSON.stringify({
+        candidates: [
+          { content: { parts: [{ inlineData: { mimeType: "audio/L16;codec=pcm;rate=24000", data: "AQID" } }] } },
+        ],
+      })
+      const responses = yield* Effect.all([
+        Speech.generate({ model: openai, text: "Hi", timestamps: false }).pipe(
+          Effect.provide(respond(new Blob([bytes]).stream(), "audio/mpeg")),
+        ),
+        Speech.generate({ model: google, text: "Hi", timestamps: false }).pipe(
+          Effect.provide(respond(gemini, "application/json")),
+        ),
+        Speech.generate({ model: deepgram, text: "Hi", timestamps: false }).pipe(
+          Effect.provide(respond(new Blob([bytes]).stream(), "audio/mpeg")),
+        ),
+      ])
+      for (const response of responses) expect(yield* response.audio.bytes()).toEqual(bytes)
+
+      const errors = yield* Effect.all(
+        [openai, google, deepgram].map((model) =>
+          Speech.generate({ model, text: "Hi", timestamps: true }).pipe(Effect.flip),
+        ),
+      ).pipe(Effect.provide(layer(() => Effect.die("an unsupported request reached the network"))))
+      expect(errors.map((error) => [error.reason._tag, "operation" in error.reason && error.reason.operation])).toEqual(
+        [
+          ["UnsupportedOperation", "media.timestamps"],
+          ["UnsupportedOperation", "media.timestamps"],
+          ["UnsupportedOperation", "media.timestamps"],
+        ],
+      )
+    }),
+  )
+
   it.effect("classifies stream failures and keeps the provider payload and HTTP context", () =>
     Effect.gen(function* () {
       const badFrame = JSON.stringify({ type: "speech.audio.delta", audio: "not base64!" })