diff --git a/extensions/ollama/ollama.live.test.ts b/extensions/ollama/ollama.live.test.ts
index a13e8c0f6613..d1d3b15d3610 100644
--- a/extensions/ollama/ollama.live.test.ts
+++ b/extensions/ollama/ollama.live.test.ts
@@ -258,7 +258,7 @@ describe.skipIf(!LIVE)("ollama live", () => {
     expect(events.map((event) => (event as { type?: string }).type)).toContain("done");
     expect(payload?.model).toBe(CHAT_MODEL);
     expect(payload?.options?.num_ctx).toBe(4096);
-    expect(payload?.options?.top_p).toBe(0.9);
+    expect(payload?.options?.top_p).toBe(1);
     expect(payload?.think).toBe(false);
     expect(payload?.keep_alive).toBe("5m");
     const properties = payload?.tools?.[0]?.function?.parameters?.properties;
diff --git a/extensions/ollama/src/stream-runtime.test.ts b/extensions/ollama/src/stream-runtime.test.ts
index 459c471ea80b..e6bbe537fa5a 100644
--- a/extensions/ollama/src/stream-runtime.test.ts
+++ b/extensions/ollama/src/stream-runtime.test.ts
@@ -2319,6 +2319,117 @@ describe("createOllamaStreamFn", () => {
     );
   });
 
+  it("sets top_p=1 for native Ollama greedy sampling requests", async () => {
+    await withMockNdjsonFetch(
+      [
+        '{"model":"m","created_at":"t","message":{"role":"assistant","content":"ok"},"done":false}',
+        '{"model":"m","created_at":"t","message":{"role":"assistant","content":""},"done":true,"prompt_eval_count":1,"eval_count":1}',
+      ],
+      async (fetchMock) => {
+        const stream = await createOllamaTestStream({
+          baseUrl: "http://ollama-host:11434",
+          model: {
+            params: {
+              num_ctx: 4096,
+              top_p: 0.9,
+              thinking: false,
+            },
+          },
+          options: { temperature: 0 },
+        });
+
+        const events = await collectStreamEvents(stream);
+        expect(events.at(-1)?.type).toBe("done");
+
+        const requestInit = getGuardedFetchCall(fetchMock).init ?? {};
+        if (typeof requestInit.body !== "string") {
+          throw new Error("Expected string request body");
+        }
+        const requestBody = JSON.parse(requestInit.body) as {
+          options: {
+            temperature?: number;
+            top_p?: number;
+          };
+        };
+        expect(requestBody.options.temperature).toBe(0);
+        expect(requestBody.options.top_p).toBe(1);
+      },
+    );
+  });
+
+  it("sets top_p=1 for native Ollama greedy requests without configured top_p", async () => {
+    await withMockNdjsonFetch(
+      [
+        '{"model":"m","created_at":"t","message":{"role":"assistant","content":"ok"},"done":false}',
+        '{"model":"m","created_at":"t","message":{"role":"assistant","content":""},"done":true,"prompt_eval_count":1,"eval_count":1}',
+      ],
+      async (fetchMock) => {
+        const stream = await createOllamaTestStream({
+          baseUrl: "http://ollama-host:11434",
+          model: {
+            params: {
+              num_ctx: 4096,
+              thinking: false,
+            },
+          },
+          options: { temperature: 0 },
+        });
+
+        const events = await collectStreamEvents(stream);
+        expect(events.at(-1)?.type).toBe("done");
+
+        const requestInit = getGuardedFetchCall(fetchMock).init ?? {};
+        if (typeof requestInit.body !== "string") {
+          throw new Error("Expected string request body");
+        }
+        const requestBody = JSON.parse(requestInit.body) as {
+          options: {
+            temperature?: number;
+            top_p?: number;
+          };
+        };
+        expect(requestBody.options.temperature).toBe(0);
+        expect(requestBody.options.top_p).toBe(1);
+      },
+    );
+  });
+
+  it("preserves configured top_p for native Ollama non-greedy sampling requests", async () => {
+    await withMockNdjsonFetch(
+      [
+        '{"model":"m","created_at":"t","message":{"role":"assistant","content":"ok"},"done":false}',
+        '{"model":"m","created_at":"t","message":{"role":"assistant","content":""},"done":true,"prompt_eval_count":1,"eval_count":1}',
+      ],
+      async (fetchMock) => {
+        const stream = await createOllamaTestStream({
+          baseUrl: "http://ollama-host:11434",
+          model: {
+            params: {
+              top_p: 0.9,
+            },
+          },
+          options: { temperature: 0.2 },
+        });
+
+        const events = await collectStreamEvents(stream);
+        expect(events.at(-1)?.type).toBe("done");
+
+        const requestInit = getGuardedFetchCall(fetchMock).init ?? {};
+        if (typeof requestInit.body !== "string") {
+          throw new Error("Expected string request body");
+        }
+        const requestBody = JSON.parse(requestInit.body) as {
+          options: {
+            temperature?: number;
+            top_p?: number;
+          };
+        };
+        expect(requestBody.options.temperature).toBe(0.2);
+        expect(requestBody.options.top_p).toBe(0.9);
+      },
+    );
+  });
+
   it("omits num_ctx when the model has no params.num_ctx and no catalog window", async () => {
     await withMockNdjsonFetch(
       [
diff --git a/extensions/ollama/src/stream.ts b/extensions/ollama/src/stream.ts
index ca03e9bf207d..d52b4260e980 100644
--- a/extensions/ollama/src/stream.ts
+++ b/extensions/ollama/src/stream.ts
@@ -343,6 +343,18 @@ function resolveOllamaModelOptions(model: ProviderRuntimeModel): Record<string,
   return options;
 }
 
+function normalizeOllamaGreedySamplingOptions(options: Record<string, unknown>): void {
+  if (options.temperature !== 0) {
+    return;
+  }
+  if (
+    options.top_p === undefined ||
+    (typeof options.top_p === "number" && Number.isFinite(options.top_p) && options.top_p !== 1)
+  ) {
+    options.top_p = 1;
+  }
+}
+
 function resolveOllamaTopLevelParams(
   model: ProviderRuntimeModel,
 ): Record<string, unknown> | undefined {
@@ -1098,6 +1110,7 @@ export function createOllamaStreamFn(
         if (typeof options?.maxTokens === "number") {
           ollamaOptions.num_predict = options.maxTokens;
         }
+        normalizeOllamaGreedySamplingOptions(ollamaOptions);
 
         const body = buildOllamaChatRequest({
           modelId: model.id,