diff --git a/packages/ai/src/providers/amazon-bedrock.ts b/packages/ai/src/providers/amazon-bedrock.ts
index aa72ada0e..4473f46d2 100644
--- a/packages/ai/src/providers/amazon-bedrock.ts
+++ b/packages/ai/src/providers/amazon-bedrock.ts
@@ -55,7 +55,10 @@ import { transformMessages } from "./transform-messages";
 const SIGNER_OWNED_HEADERS = new Set(["host", "x-amz-date", "x-amz-content-sha256", "x-amz-security-token"]);
 
 /** Headers the Bedrock request sets itself; a caller copy in any casing duplicates them. */
-const BEDROCK_RESERVED_HEADERS = new Set(["content-type", "accept", "authorization"]);
+// `content-length` included: the fetch layer recomputes it from the serialized
+// body, so a caller value would be signed but not sent, and AWS rejects the
+// mismatch.
+const BEDROCK_RESERVED_HEADERS = new Set(["content-type", "accept", "authorization", "content-length"]);
 
 export type BedrockThinkingDisplay = "summarized" | "omitted";
 
diff --git a/packages/ai/src/providers/cursor.ts b/packages/ai/src/providers/cursor.ts
index f3fc04fc5..23bcae9af 100644
--- a/packages/ai/src/providers/cursor.ts
+++ b/packages/ai/src/providers/cursor.ts
@@ -256,6 +256,10 @@ const CURSOR_RESERVED_HEADERS = new Set([
 	// header is present, so a caller value here silently retargets the request at
 	// a different virtual host.
 	"host",
+	// The Connect body is streamed after the headers (initial frame, heartbeats,
+	// tool responses), so no caller-supplied length can describe it and an HTTP/2
+	// peer resets the stream once the body diverges.
+	"content-length",
 ]);
 
 /**
diff --git a/packages/ai/test/bedrock-caller-headers.test.ts b/packages/ai/test/bedrock-caller-headers.test.ts
index fcb3a098d..f9b251650 100644
--- a/packages/ai/test/bedrock-caller-headers.test.ts
+++ b/packages/ai/test/bedrock-caller-headers.test.ts
@@ -156,6 +156,9 @@ describe("Bedrock caller headers", () => {
 					"Content-Type": "text/plain",
 					Accept: "text/plain",
 					Host: "evil.example.com",
+					// Recomputed by the fetch layer from the serialized body, so a caller
+					// value would be signed but never sent.
+					"Content-Length": "999",
 					"X-Trace": "kept",
 				},
 			});
@@ -165,7 +168,7 @@ describe("Bedrock caller headers", () => {
 		const headers = seen.headers ?? {};
 		const names = Object.keys(headers).map(name => name.toLowerCase());
 		// Each field appears exactly once, whatever casing the caller used.
-		for (const field of ["content-type", "accept", "host"]) {
+		for (const field of ["content-type", "accept", "host", "content-length"]) {
 			expect(names.filter(name => name === field).length).toBeLessThanOrEqual(1);
 		}
 		expect(headers["content-type"]).toBe("application/json");
diff --git a/packages/ai/test/cursor-caller-headers.test.ts b/packages/ai/test/cursor-caller-headers.test.ts
index 15d37f251..14b21613a 100644
--- a/packages/ai/test/cursor-caller-headers.test.ts
+++ b/packages/ai/test/cursor-caller-headers.test.ts
@@ -164,12 +164,16 @@ describe("Cursor caller headers reach the wire", () => {
 			"Content-Type": "text/plain",
 			TE: "gzip",
 			"X-Request-Id": "forged",
+			// The Connect body is streamed after the headers, so no caller length can
+			// describe it; an HTTP/2 peer resets the stream once the body diverges.
+			"Content-Length": "999",
 			"x-trace": "kept",
 		});
 		expect(sent.authorization).toBe("Bearer test-token");
 		expect(sent["content-type"]).toBe("application/connect+proto");
 		expect(sent.te).toBe("trailers");
 		expect(sent["x-request-id"]).not.toBe("forged");
+		expect(sent["content-length"]).toBeUndefined();
 		expect(sent["x-trace"]).toBe("kept");
 	});