diff --git a/src/config.test.ts b/src/config.test.ts
index 32d488de0..4b86d86f3 100644
--- a/src/config.test.ts
+++ b/src/config.test.ts
@@ -1467,6 +1467,25 @@ describe("buildOpenAISource", () => {
     });
   });
 
+  test("flows temperature and top_p together when both are present", () => {
+    // Settings load rejects both knobs. This builder still forwards a pair
+    // it is given. DeepSeek V4 model-card defaults reach the wire because
+    // the adapter writes top_p 0.95 and temperature 1.0 when each body
+    // field is absent, not because this merge supplies those defaults.
+    const source = buildOpenAISource({
+      id: "fp",
+      baseURL: "https://fp/v1",
+      apiKey: "k",
+      model: "m",
+      temperature: 0.7,
+      topP: 0.9,
+    });
+    expect(source.defaults).toEqual({
+      maxTokens: SOURCE_MAX_TOKENS,
+      providerOptions: { temperature: 0.7, top_p: 0.9 },
+    });
+  });
+
   test("coexists temperature with reasoning_effort in one providerOptions", () => {
     const source = buildOpenAISource({
       id: "fp",
diff --git a/src/config/settings.test.ts b/src/config/settings.test.ts
index 03526dbf5..6ae6eb026 100644
--- a/src/config/settings.test.ts
+++ b/src/config/settings.test.ts
@@ -72,7 +72,7 @@ test("invalid token settings cannot be loaded or overwrite a saved provider", as
   }
 });
 
-test("provider settings reject simultaneous sampling fields but preserve zero", () => {
+test("provider settings reject simultaneous sampling fields but preserve zero", async () => {
   const provider = {
     baseURL: "https://custom.example/v1",
     keyless: true,
@@ -85,6 +85,19 @@ test("provider settings reject simultaneous sampling fields but preserve zero",
   expect(isSettings({ providers: { custom: { ...provider, topP: 0 } } })).toBe(
     false,
   );
+  // The exclusion is enforced at load, not just by isSettings — a persisted
+  // file with both knobs fails to load.
+  const cwd = await mkdtemp(join(tmpdir(), "both-sampling-knobs-"));
+  try {
+    const path = join(cwd, "settings.json");
+    await writeFile(
+      path,
+      JSON.stringify({ providers: { custom: { ...provider, topP: 0 } } }),
+    );
+    await expect(loadSettings(path)).rejects.toThrow();
+  } finally {
+    await rm(cwd, { recursive: true, force: true });
+  }
 });
 
 afterEach(() => {
diff --git a/src/config/settings.ts b/src/config/settings.ts
index f099cdc29..f58363b83 100644
--- a/src/config/settings.ts
+++ b/src/config/settings.ts
@@ -43,7 +43,10 @@ export interface ProviderSettings {
   // Per-call output cap, overriding SOURCE_MAX_TOKENS when set.
   maxTokens?: number;
   // Sampling temperature (0..2, OpenAI-compatible); mutually exclusive with
-  // topP — never send both on the wire.
+  // topP in provider settings — load rejects both (see
+  // ProviderInferenceOptionsSchema). The wire may still carry both when a
+  // provider adapter mandates it (DeepSeek V4 backfills absent fields from
+  // its model-card defaults).
   temperature?: number;
   // Sampling top-p (0..1, OpenAI-compatible); mutually exclusive with
   // temperature.