diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index 705af3d5c1b5..303ff11fdfd8 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -516,12 +516,20 @@ export function message(msgs: ModelMessage[], model: Provider.Model, options: Re
   return msgs
 }
 
+const GEMINI_MODELS_WITH_SAMPLING_DEFAULTS = [
+  /gemini-2[.-]5(?:[.-]|$)/,
+  /gemini-3-(?:flash|pro)(?:[.-]|$)/,
+  /gemini-3[.-]1(?:[.-]|$)/,
+  /gemini-3[.-]5-flash(?!-lite)(?:[.-]|$)/,
+]
+
 export function temperature(model: Provider.Model) {
-  const id = model.id.toLowerCase()
+  const id = model.api.id.toLowerCase()
   if (id.includes("north-mini-code")) return 1.0
   if (id.includes("qwen")) return 0.55
   if (id.includes("claude")) return undefined
-  if (id.includes("gemini")) return 1.0
+  if (id.includes("gemini"))
+    return GEMINI_MODELS_WITH_SAMPLING_DEFAULTS.some((model) => model.test(id)) ? 1.0 : undefined
   if (id.includes("glm-4.6")) return 1.0
   if (id.includes("glm-4.7")) return 1.0
   if (id.includes("minimax-m2")) return 1.0
@@ -536,21 +544,24 @@ export function temperature(model: Provider.Model) {
 }
 
 export function topP(model: Provider.Model) {
-  const id = model.id.toLowerCase()
+  const id = model.api.id.toLowerCase()
   if (id.includes("qwen")) return 1
-  if (["minimax-m2", "gemini", "kimi-k2.5", "kimi-k2p5", "kimi-k2-5"].some((s) => id.includes(s))) {
+  if (id.includes("gemini"))
+    return GEMINI_MODELS_WITH_SAMPLING_DEFAULTS.some((model) => model.test(id)) ? 0.95 : undefined
+  if (["minimax-m2", "kimi-k2.5", "kimi-k2p5", "kimi-k2-5"].some((s) => id.includes(s))) {
     return 0.95
   }
   return undefined
 }
 
 export function topK(model: Provider.Model) {
-  const id = model.id.toLowerCase()
+  const id = model.api.id.toLowerCase()
   if (id.includes("minimax-m2")) {
     if (["m2.", "m25", "m21"].some((s) => id.includes(s))) return 40
     return 20
   }
-  if (id.includes("gemini")) return 64
+  if (id.includes("gemini"))
+    return GEMINI_MODELS_WITH_SAMPLING_DEFAULTS.some((model) => model.test(id)) ? 64 : undefined
   return undefined
 }
 
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index 93e166c4a8c9..0b88fa59dff8 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -3186,7 +3186,69 @@ describe("ProviderTransform.message - cache control on gateway", () => {
 
 describe("ProviderTransform.temperature - Cohere North", () => {
   test("defaults north-mini-code models to 1.0", () => {
-    expect(ProviderTransform.temperature({ id: "cohere/North-Mini-Code-1-0-latest" } as any)).toBe(1.0)
+    expect(
+      ProviderTransform.temperature({
+        id: "cohere/North-Mini-Code-1-0-latest",
+        api: { id: "North-Mini-Code-1-0-latest" },
+      } as any),
+    ).toBe(1.0)
+  })
+})
+
+describe("ProviderTransform sampling defaults - Gemini", () => {
+  const model = (id: string) =>
+    ({
+      id: `google/${id}`,
+      api: { id },
+    }) as any
+
+  const alias = (id: string, apiID: string) =>
+    ({
+      id,
+      api: { id: apiID },
+    }) as any
+
+  test.each([
+    "gemini-3.5-flash-lite",
+    "gemini-3-5-flash-lite",
+    "gemini-3.6-flash",
+    "gemini-3-6-flash",
+    "gemini-4-pro",
+    "gemini-future",
+  ])("omits deprecated sampling controls for %s", (id) => {
+    expect(ProviderTransform.temperature(model(id))).toBeUndefined()
+    expect(ProviderTransform.topP(model(id))).toBeUndefined()
+    expect(ProviderTransform.topK(model(id))).toBeUndefined()
+  })
+
+  test.each([
+    "gemini-2.5-flash",
+    "gemini-2.5-pro",
+    "gemini-2.5-flash-lite",
+    "gemini-2-5-flash-lite",
+    "gemini-3-flash-preview",
+    "gemini-3-pro-image",
+    "gemini-3.1-flash-lite",
+    "gemini-3.1-pro-preview",
+    "gemini-3-1-pro-preview",
+    "gemini-3.5-flash",
+    "gemini-3-5-flash",
+  ])("preserves sampling defaults for %s", (id) => {
+    expect(ProviderTransform.temperature(model(id))).toBe(1)
+    expect(ProviderTransform.topP(model(id))).toBe(0.95)
+    expect(ProviderTransform.topK(model(id))).toBe(64)
+  })
+
+  test("uses the API model ID for configured aliases", () => {
+    const deprecated = alias("google/gemini-3.5-flash", "google/gemini-3.6-flash")
+    expect(ProviderTransform.temperature(deprecated)).toBeUndefined()
+    expect(ProviderTransform.topP(deprecated)).toBeUndefined()
+    expect(ProviderTransform.topK(deprecated)).toBeUndefined()
+
+    const supported = alias("my-gemini", "google/gemini-2.5-flash")
+    expect(ProviderTransform.temperature(supported)).toBe(1)
+    expect(ProviderTransform.topP(supported)).toBe(0.95)
+    expect(ProviderTransform.topK(supported)).toBe(64)
   })
 })