diff --git a/packages/paperclip-runner/README.md b/packages/paperclip-runner/README.md
index 24808690a98..02271ebc583 100644
--- a/packages/paperclip-runner/README.md
+++ b/packages/paperclip-runner/README.md
@@ -485,6 +485,12 @@ stable free-text option IDs. Legacy callers remain supported. Calls that supply
 both forms must describe the same complete form; partial forms remain invalid.
 The native recovery bridge uses the same projection for answer delivery.
 
+OpenCode 1.18.34 native questions allow a written answer by default when `custom`
+is omitted. The driver preserves that default and explicit `custom:false`; the
+native flag takes precedence over the legacy `allowCustom` alias. Choice options
+remain intact. Questions without options remain text-only, without a separate
+custom-answer field. See the [pinned native question contract](https://github.com/anomalyco/opencode/blob/v1.18.34/packages/schema/src/v1/question.ts).
+
 The server validates canonical answer constraints before persistence. Regex
 matching runs in isolated workers with a one-second deadline and at most four
 active workers. A timeout or capacity error leaves the question pending. The
diff --git a/packages/paperclip-runner/src/drivers/opencode/opencode-question-normalization.test.ts b/packages/paperclip-runner/src/drivers/opencode/opencode-question-normalization.test.ts
new file mode 100644
index 00000000000..9969fc30c0b
--- /dev/null
+++ b/packages/paperclip-runner/src/drivers/opencode/opencode-question-normalization.test.ts
@@ -0,0 +1,37 @@
+import { describe, expect, it } from "vitest";
+import { parsePaperclipQuestionResponse } from "../../contracts/question-set.js";
+import { normalizeOpenCodeQuestionSet } from "./opencode-server-driver.js";
+
+const question = { id: "reference", header: "Reference", question: "Which reference should appear in the note?",
+  options: [{ label: "No reference", description: "Do not include a reference" }] };
+const response = { schema: "paperclip.question_response.v1", answers: { reference: { customText: "Use AMBERexact." } } };
+
+describe("OpenCode native written-answer defaults", () => {
+  it.each([
+    { name: "omitted native default", fields: {}, enabled: true },
+    { name: "explicit native true", fields: { custom: true }, enabled: true },
+    { name: "explicit native false", fields: { custom: false }, enabled: false },
+    { name: "legacy alias true", fields: { allowCustom: true }, enabled: true },
+    { name: "legacy alias false", fields: { allowCustom: false }, enabled: false },
+    { name: "native opt-out takes precedence", fields: { custom: false, allowCustom: true }, enabled: false },
+  ])("preserves $name without changing the supplied choice", ({ fields, enabled }) => {
+    const set = normalizeOpenCodeQuestionSet([{ ...question, ...fields }]);
+    expect(set.questions[0]).toMatchObject({ id: "reference", prompt: question.question, answerMode: "single_select",
+      options: [{ id: "option-1", label: "No reference", description: "Do not include a reference" }] });
+    if (enabled) {
+      expect(set.questions[0].customAnswer).toEqual({ enabled: true, label: "Other", placeholder: "Enter another answer" });
+      expect(parsePaperclipQuestionResponse(set, response)).toEqual(response);
+    } else {
+      expect(set.questions[0]).not.toHaveProperty("customAnswer");
+      expect(() => parsePaperclipQuestionResponse(set, response)).toThrow("custom answers are not enabled");
+    }
+  });
+  it.each([undefined, true, false])("keeps a question without choices text-only (custom=%s)", custom => {
+    const set = normalizeOpenCodeQuestionSet([{ ...question, options: [], ...(custom === undefined ? {} : { custom }) }]);
+    expect(set.questions[0]).toMatchObject({ id: "reference", answerMode: "text" });
+    expect(set.questions[0]).not.toHaveProperty("options");
+    expect(set.questions[0]).not.toHaveProperty("customAnswer");
+    expect(parsePaperclipQuestionResponse(set, { ...response, answers: { reference: { text: "Use AMBERexact." } } }))
+      .toEqual({ ...response, answers: { reference: { text: "Use AMBERexact." } } });
+  });
+});
diff --git a/packages/paperclip-runner/src/drivers/opencode/opencode-server-driver.test.ts b/packages/paperclip-runner/src/drivers/opencode/opencode-server-driver.test.ts
index f89dc89059c..58af69bad4b 100644
--- a/packages/paperclip-runner/src/drivers/opencode/opencode-server-driver.test.ts
+++ b/packages/paperclip-runner/src/drivers/opencode/opencode-server-driver.test.ts
@@ -1799,7 +1799,7 @@ describe("OpenCodeServerDriver", () => {
     await recovered!.session!.close({ reason: "recovery-test" });
   });
 
-  it("normalizes native question.asked events and replies with ordered OpenCode answer arrays", async () => {
+  it("preserves omitted native custom defaults and replies with ordered OpenCode answer arrays", async () => {
     await chmod(fixture, 0o755);
     const root = await mkdtemp(join(tmpdir(), "paperclip-opencode-question-"));
     const workspace = await mkdtemp(
diff --git a/packages/paperclip-runner/src/drivers/opencode/opencode-server-driver.ts b/packages/paperclip-runner/src/drivers/opencode/opencode-server-driver.ts
index 45fb78ccefc..6576fe894e7 100644
--- a/packages/paperclip-runner/src/drivers/opencode/opencode-server-driver.ts
+++ b/packages/paperclip-runner/src/drivers/opencode/opencode-server-driver.ts
@@ -2654,6 +2654,7 @@ export function normalizeOpenCodeQuestionSet(
             ? { description: text(option.description).slice(0, 4_000) }
             : {}),
         }));
+      const custom = question.custom ?? question.allowCustom ?? true;
       return {
         id: openCodeQuestionId(question, index),
         ...(text(question.header)
@@ -2674,7 +2675,7 @@ export function normalizeOpenCodeQuestionSet(
               ? "multi_select"
               : "single_select",
         ...(options.length > 0 ? { options } : {}),
-        ...(question.custom === true || question.allowCustom === true
+        ...(options.length > 0 && custom === true
           ? {
               customAnswer: {
                 enabled: true,
diff --git a/packages/paperclip-runner/test/fixtures/fake-opencode-server.mjs b/packages/paperclip-runner/test/fixtures/fake-opencode-server.mjs
index 3b03d4d52e2..38da64e96a1 100644
--- a/packages/paperclip-runner/test/fixtures/fake-opencode-server.mjs
+++ b/packages/paperclip-runner/test/fixtures/fake-opencode-server.mjs
@@ -41,7 +41,6 @@ function nativeQuestion() {
             description: "Deploy directly to production.",
           },
         ],
-        custom: true,
       },
       {
         id: "regions",