diff --git a/packages/opencode/src/session/retry.ts b/packages/opencode/src/session/retry.ts
index 4139665bd2bd..f0d0fcd4c2d9 100644
--- a/packages/opencode/src/session/retry.ts
+++ b/packages/opencode/src/session/retry.ts
@@ -58,7 +58,12 @@ export function delay(attempt: number, error?: SessionV1.APIError) {
         }
       }
 
-      return cap(RETRY_INITIAL_DELAY * Math.pow(RETRY_BACKOFF_FACTOR, attempt - 1))
+      // Headers were present but carried no usable retry-after hint. Apply the
+      // same 30s cap as the no-headers branch so a flaky 5xx with normal
+      // response headers (content-type, date, ...) cannot grow the backoff
+      // past RETRY_MAX_DELAY_NO_HEADERS. Without this, attempt 10 waits ~17min,
+      // attempt 15 ~9h, attempt 20 ~12d.
+      return cap(Math.min(RETRY_INITIAL_DELAY * Math.pow(RETRY_BACKOFF_FACTOR, attempt - 1), RETRY_MAX_DELAY_NO_HEADERS))
     }
   }
 
diff --git a/packages/opencode/test/session/retry.test.ts b/packages/opencode/test/session/retry.test.ts
index e53a6c1f18ee..3c78b78f0fb0 100644
--- a/packages/opencode/test/session/retry.test.ts
+++ b/packages/opencode/test/session/retry.test.ts
@@ -39,6 +39,19 @@ describe("session.retry.delay", () => {
     expect(delays).toStrictEqual([2000, 4000, 8000, 16000, 30000, 30000, 30000, 30000, 30000, 30000])
   })
 
+  test("caps delay at 30 seconds when headers present but lack retry-after", () => {
+    // Real 5xx responses almost always carry headers (content-type, date, ...).
+    // The fallback path must still respect RETRY_MAX_DELAY_NO_HEADERS.
+    const error = apiError({ "content-type": "application/json" })
+    const delays = Array.from({ length: 10 }, (_, index) => SessionRetry.delay(index + 1, error))
+    expect(delays).toStrictEqual([2000, 4000, 8000, 16000, 30000, 30000, 30000, 30000, 30000, 30000])
+  })
+
+  test("caps delay at 30 seconds when retry-after header is unparseable", () => {
+    const error = apiError({ "retry-after": "not-a-number" })
+    expect(SessionRetry.delay(8, error)).toBe(30000)
+  })
+
   test("prefers retry-after-ms when shorter than exponential", () => {
     const error = apiError({ "retry-after-ms": "1500" })
     expect(SessionRetry.delay(4, error)).toBe(1500)