diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index 0f85d44f209b..bbf1dbde6654 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -1108,6 +1108,23 @@ const layer = Layer.effect(
               (part) => part.type === "tool" && !part.metadata?.providerExecuted && !isOrphanedInterruptedTool(part),
             ) ?? false
 
+          const hasAssistantOutput =
+            (lastAssistantMsg?.parts.length ?? 0) > 2 ||
+            (lastAssistantMsg?.parts.some(
+              (part) => part.type === "text" || part.type === "reasoning" || part.type === "tool",
+            ) ??
+              false)
+
+          if (lastAssistant?.finish === "unknown" && !hasAssistantOutput && !lastAssistant.error) {
+            lastAssistant.error = MessageV2.fromError(new Error("Provider returned an empty response"), {
+              providerID: lastAssistant.providerID,
+            })
+            yield* sessions.updateMessage(lastAssistant)
+            yield* events.publish(Session.Event.Error, { sessionID, error: lastAssistant.error })
+            yield* status.set(sessionID, { type: "idle" })
+            break
+          }
+
           if (
             lastAssistant?.finish &&
             !["tool-calls", "unknown"].includes(lastAssistant.finish) &&
diff --git a/packages/opencode/test/cli/run/run-process.test.ts b/packages/opencode/test/cli/run/run-process.test.ts
index d2d4bae87921..85f7e5035077 100644
--- a/packages/opencode/test/cli/run/run-process.test.ts
+++ b/packages/opencode/test/cli/run/run-process.test.ts
@@ -104,6 +104,21 @@ describe("opencode run (non-interactive subprocess)", () => {
     60_000,
   )
 
+  // Regression for empty provider responses: an unknown finish with no text,
+  // reasoning, or tool call must fail the turn instead of spinning forever.
+  cliIt.concurrent(
+    "exits nonzero promptly when the provider returns an empty unknown response",
+    ({ llm, opencode }) =>
+      Effect.gen(function* () {
+        yield* llm.push(reply().unknown())
+        const result = yield* opencode.run("empty response", { timeoutMs: 10_000 })
+        expect(result.exitCode).not.toBe(0)
+        expect(result.durationMs).toBeLessThan(10_000)
+        expect(result.stderr).toContain("Provider returned an empty response")
+      }),
+    30_000,
+  )
+
   // --format json puts one JSON object per line on stdout for each emitted
   // event. Consumers (CI scripts, tooling) parse this stream. Asserts the
   // shape so a future event-emit change has to update this expectation.
diff --git a/packages/opencode/test/lib/llm-server.ts b/packages/opencode/test/lib/llm-server.ts
index 245acc7280f5..1b9cdde26e93 100644
--- a/packages/opencode/test/lib/llm-server.ts
+++ b/packages/opencode/test/lib/llm-server.ts
@@ -493,6 +493,14 @@ export class Reply {
     return this
   }
 
+  unknown() {
+    this.#finish = "unknown"
+    this.#hang = false
+    this.#error = undefined
+    this.#reset = false
+    return this
+  }
+
   contentFilter() {
     this.#finish = "content_filter"
     this.#hang = false