diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index 009b8fba..bfe1d1f7 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -505,6 +505,7 @@ export function variants(model: Provider.Model): Record<string, Record<string, a
   if (!model.capabilities.reasoning) return {}
 
   const id = model.id.toLowerCase()
+  const pid = model.providerID.toLowerCase()
   const adaptiveEfforts = anthropicAdaptiveEfforts(model.api.id)
   if (
     id.includes("deepseek") ||
@@ -515,8 +516,20 @@ export function variants(model: Provider.Model): Record<string, Record<string, a
     id.includes("k2p5") ||
     id.includes("qwen") ||
     id.includes("big-pickle")
-  )
-    return {}
+  ) {
+    // Custom providers may proxy these models — only exclude built-in providers
+    // where the providerID matches the model family.
+    const isBuiltIn =
+      (id.includes("deepseek") && pid.includes("deepseek")) ||
+      (id.includes("minimax") && pid.includes("minimax")) ||
+      (id.includes("glm") && pid.includes("glm")) ||
+      (id.includes("mistral") && pid.includes("mistral")) ||
+      (id.includes("kimi") && pid.includes("kimi")) ||
+      (id.includes("k2p5") && pid.includes("k2p5")) ||
+      (id.includes("qwen") && pid.includes("qwen")) ||
+      (id.includes("big-pickle") && pid.includes("big-pickle"))
+    if (isBuiltIn) return {}
+  }
 
   // see: https://docs.x.ai/docs/guides/reasoning#control-how-hard-the-model-thinks
   if (id.includes("grok") && id.includes("grok-3-mini")) {
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index 89231f27..8415c54d 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -2720,6 +2720,77 @@ describe("ProviderTransform.variants", () => {
       expect(result.low).toEqual({ reasoningEffort: "low" })
       expect(result.high).toEqual({ reasoningEffort: "high" })
     })
+
+    test("custom provider with deepseek model ID returns variants", () => {
+      const model = createMockModel({
+        id: "my-provider/deepseek-v4-pro",
+        providerID: "my-provider",
+        api: {
+          id: "deepseek-v4-pro",
+          url: "https://my-api.example.com",
+          npm: "@ai-sdk/openai-compatible",
+        },
+      })
+      const result = ProviderTransform.variants(model)
+      expect(Object.keys(result)).toEqual(["low", "medium", "high"])
+      expect(result.low).toEqual({ reasoningEffort: "low" })
+    })
+
+    test("custom provider with minimax model ID returns variants", () => {
+      const model = createMockModel({
+        id: "my-provider/minimax-text-01",
+        providerID: "my-provider",
+        api: {
+          id: "minimax-text-01",
+          url: "https://my-api.example.com",
+          npm: "@ai-sdk/openai-compatible",
+        },
+      })
+      const result = ProviderTransform.variants(model)
+      expect(Object.keys(result)).toEqual(["low", "medium", "high"])
+    })
+
+    test("custom provider with glm model ID returns variants", () => {
+      const model = createMockModel({
+        id: "my-provider/glm-4",
+        providerID: "my-provider",
+        api: {
+          id: "glm-4",
+          url: "https://my-api.example.com",
+          npm: "@ai-sdk/openai-compatible",
+        },
+      })
+      const result = ProviderTransform.variants(model)
+      expect(Object.keys(result)).toEqual(["low", "medium", "high"])
+    })
+
+    test("custom provider with qwen model ID returns variants", () => {
+      const model = createMockModel({
+        id: "my-provider/qwen-max",
+        providerID: "my-provider",
+        api: {
+          id: "qwen-max",
+          url: "https://my-api.example.com",
+          npm: "@ai-sdk/openai-compatible",
+        },
+      })
+      const result = ProviderTransform.variants(model)
+      expect(Object.keys(result)).toEqual(["low", "medium", "high"])
+    })
+
+    test("custom provider with kimi model ID returns variants", () => {
+      const model = createMockModel({
+        id: "my-provider/kimi-latest",
+        providerID: "my-provider",
+        api: {
+          id: "kimi-latest",
+          url: "https://my-api.example.com",
+          npm: "@ai-sdk/openai-compatible",
+        },
+      })
+      const result = ProviderTransform.variants(model)
+      expect(Object.keys(result)).toEqual(["low", "medium", "high"])
+    })
   })
 
   describe("@ai-sdk/azure", () => {