diff --git a/docs/tasks/streams.mdx b/docs/tasks/streams.mdx
index 8c33a30e2..26c7c906b 100644
--- a/docs/tasks/streams.mdx
+++ b/docs/tasks/streams.mdx
@@ -655,7 +655,7 @@ If `onError` is omitted, reconnect still returns `null` and continues without ca
 
 `baseURL` supports optional path prefixes and trailing slashes; both trigger and stream URLs
 are normalized consistently, surrounding whitespace is trimmed before normalization, and
-the resulting value must not be empty.
+the resulting value must not be empty. The value must also be a valid absolute URL.
 
 For richer TypeScript ergonomics in app code, `@trigger.dev/ai` also exports:
 
diff --git a/packages/ai/CHANGELOG.md b/packages/ai/CHANGELOG.md
index 24d16d771..34b4d6ac6 100644
--- a/packages/ai/CHANGELOG.md
+++ b/packages/ai/CHANGELOG.md
@@ -22,3 +22,4 @@
 - Added consistent baseURL normalization for trigger and stream endpoints (including path prefixes and trailing slashes).
 - Added surrounding-whitespace trimming for `baseURL` before endpoint normalization.
 - Added explicit validation that `baseURL` is non-empty after normalization.
+- Added explicit validation that `baseURL` is a valid absolute URL.
diff --git a/packages/ai/README.md b/packages/ai/README.md
index 96c603174..3fa5acc46 100644
--- a/packages/ai/README.md
+++ b/packages/ai/README.md
@@ -161,6 +161,7 @@ both cleanup steps (`set` inactive state and `delete`) even if one of them fails
 - Trailing slashes are normalized automatically before trigger/stream requests.
 - Surrounding whitespace is trimmed before normalization.
 - `baseURL` must not be empty after trimming/normalization.
+- `baseURL` must be a valid absolute URL.
 
 ## `ai.tool(...)` example
 
diff --git a/packages/ai/src/chatTransport.test.ts b/packages/ai/src/chatTransport.test.ts
index 6a4fdda9d..36722f492 100644
--- a/packages/ai/src/chatTransport.test.ts
+++ b/packages/ai/src/chatTransport.test.ts
@@ -620,6 +620,28 @@ describe("TriggerChatTransport", function () {
     }).toThrowError("baseURL must not be empty");
   });
 
+  it("throws when baseURL is not a valid absolute URL", function () {
+    expect(function () {
+      new TriggerChatTransport({
+        task: "chat-task",
+        accessToken: "pk_trigger",
+        baseURL: "not-a-valid-url",
+        stream: "chat-stream",
+      });
+    }).toThrowError("baseURL must be a valid absolute URL");
+  });
+
+  it("throws when baseURL is a relative path", function () {
+    expect(function () {
+      new TriggerChatTransport({
+        task: "chat-task",
+        accessToken: "pk_trigger",
+        baseURL: "/relative/path",
+        stream: "chat-stream",
+      });
+    }).toThrowError("baseURL must be a valid absolute URL");
+  });
+
   it("combines path prefixes with run and stream URL encoding", async function () {
     let observedTriggerPath: string | undefined;
     let observedStreamPath: string | undefined;
@@ -2745,6 +2767,17 @@ describe("TriggerChatTransport", function () {
     }).toThrowError("baseURL must not be empty");
   });
 
+  it("throws from factory when baseURL is not a valid absolute URL", function () {
+    expect(function () {
+      createTriggerChatTransport({
+        task: "chat-task",
+        accessToken: "pk_trigger",
+        baseURL: "invalid-base-url",
+        stream: "chat-stream",
+      });
+    }).toThrowError("baseURL must be a valid absolute URL");
+  });
+
   it("continues streaming when onTriggeredRun callback throws", async function () {
     let callbackCalled = false;
     const errors: TriggerChatTransportError[] = [];
diff --git a/packages/ai/src/chatTransport.ts b/packages/ai/src/chatTransport.ts
index f934d13c5..f86c5a12f 100644
--- a/packages/ai/src/chatTransport.ts
+++ b/packages/ai/src/chatTransport.ts
@@ -466,6 +466,12 @@ function normalizeBaseUrl(baseURL: string) {
     throw new Error("baseURL must not be empty");
   }
 
+  try {
+    new URL(normalizedBaseUrl);
+  } catch {
+    throw new Error("baseURL must be a valid absolute URL");
+  }
+
   return normalizedBaseUrl;
 }