diff --git a/packages/opencode/src/plugin/github-copilot/models.ts b/packages/opencode/src/plugin/github-copilot/models.ts
index 8cafa567150..61631826704 100644
--- a/packages/opencode/src/plugin/github-copilot/models.ts
+++ b/packages/opencode/src/plugin/github-copilot/models.ts
@@ -79,6 +79,17 @@ type CopilotModel = Omit<Model, "api"> & {
 const decodeModels = Schema.decodeUnknownSync(schema)
 const decodeItem = Schema.decodeUnknownOption(item)
 
+// Copilot serves these families only on /responses, so route them there when the
+// live model metadata does not advertise supported_endpoints. Older chat-only
+// families (gpt-5-mini, gpt-4*, Claude) stay on chat.
+export function fallbackEndpoint(modelID: string): "responses" | undefined {
+  const match = /^gpt-(\d+)/.exec(modelID)
+  if (match && Number(match[1]) >= 5 && !modelID.startsWith("gpt-5-mini")) return "responses"
+  if (modelID.startsWith("grok-") || modelID.startsWith("gemini-") || modelID.startsWith("mai-code-"))
+    return "responses"
+  return undefined
+}
+
 function build(key: string, remote: SelectableItem, url: string, prev?: Model): Model {
   const reasoning =
     !!remote.capabilities.supports.adaptive_thinking ||
diff --git a/packages/opencode/src/provider/provider.ts b/packages/opencode/src/provider/provider.ts
index 867ef2ca2fa..da6481ea078 100644
--- a/packages/opencode/src/provider/provider.ts
+++ b/packages/opencode/src/provider/provider.ts
@@ -8,6 +8,7 @@ import { NoSuchModelError, type Provider as SDK } from "ai"
 import { Npm } from "@opencode-ai/core/npm"
 import { Hash } from "@opencode-ai/core/util/hash"
 import { Plugin } from "../plugin"
+import { CopilotModels } from "../plugin/github-copilot/models"
 import { serviceUse } from "@opencode-ai/core/effect/service-use"
 import { type LanguageModelV3 } from "@ai-sdk/provider"
 import { ModelsDev } from "@opencode-ai/core/models-dev"
@@ -237,8 +238,7 @@ function custom(dep: CustomDep): Record<string, CustomLoader> {
             if (model.api.endpoint === "responses" && sdk.responses) return sdk.responses(modelID)
             if (model.api.endpoint === "chat" && sdk.chat) return sdk.chat(modelID)
           }
-          const match = /^gpt-(\d+)/.exec(modelID)
-          if (match && Number(match[1]) >= 5 && !modelID.startsWith("gpt-5-mini")) return sdk.responses(modelID)
+          if (CopilotModels.fallbackEndpoint(modelID) === "responses") return sdk.responses(modelID)
           return sdk.chat(modelID)
         },
         options: {},
@@ -1497,11 +1497,15 @@ const layer = Layer.effect(
               model.provider?.npm ??
               provider.npm ??
               existingModel?.api.npm ??
-              // Config-defined gateway models bypass fromModelsDevModel, so resolve the
-              // native passthrough npm here before falling back to the catalog default.
-              cloudflareGatewayNpm(providerID, apiID) ??
-              modelsDev[providerID]?.npm ??
-              "@ai-sdk/openai-compatible"
+              // Provider-specific SDKs that must not inherit the models.dev catalog
+              // default: GitHub Copilot needs its bundled SDK, and gateway models
+              // bypass fromModelsDevModel so they resolve their native passthrough npm
+              // before falling back to the catalog default.
+              (providerID === ProviderV2.ID.githubCopilot
+                ? "@ai-sdk/github-copilot"
+                : (cloudflareGatewayNpm(providerID, apiID) ??
+                  modelsDev[providerID]?.npm ??
+                  "@ai-sdk/openai-compatible"))
             const name = iife(() => {
               if (model.name) return model.name
               if (model.id && model.id !== modelID) return modelID
diff --git a/packages/opencode/test/plugin/github-copilot-models.test.ts b/packages/opencode/test/plugin/github-copilot-models.test.ts
index d968402e3b8..ad2938b91dd 100644
--- a/packages/opencode/test/plugin/github-copilot-models.test.ts
+++ b/packages/opencode/test/plugin/github-copilot-models.test.ts
@@ -490,3 +490,14 @@ test("remaps fallback oauth model urls to the enterprise host", async () => {
   expect(models.claude.api.url).toBe("https://copilot-api.ghe.example.com")
   expect(models.claude.api.npm).toBe("@ai-sdk/github-copilot")
 })
+
+test("falls back to responses for Copilot families that require it", () => {
+  expect(CopilotModels.fallbackEndpoint("gpt-5.6-sol")).toBe("responses")
+  expect(CopilotModels.fallbackEndpoint("grok-4.5")).toBe("responses")
+  expect(CopilotModels.fallbackEndpoint("grok-4.6")).toBe("responses")
+  expect(CopilotModels.fallbackEndpoint("gemini-3.5-flash")).toBe("responses")
+  expect(CopilotModels.fallbackEndpoint("mai-code-1.1-flash")).toBe("responses")
+  expect(CopilotModels.fallbackEndpoint("gpt-5-mini")).toBeUndefined()
+  expect(CopilotModels.fallbackEndpoint("gpt-4o")).toBeUndefined()
+  expect(CopilotModels.fallbackEndpoint("claude-sonnet-4.6")).toBeUndefined()
+})
diff --git a/packages/opencode/test/provider/provider.test.ts b/packages/opencode/test/provider/provider.test.ts
index 32d4e3a39b1..c9156e71b72 100644
--- a/packages/opencode/test/provider/provider.test.ts
+++ b/packages/opencode/test/provider/provider.test.ts
@@ -1348,6 +1348,31 @@ it.instance(
   },
 )
 
+it.instance(
+  "custom github-copilot models use the bundled Copilot SDK",
+  Effect.gen(function* () {
+    yield* set("GITHUB_TOKEN", "test-token")
+    const providers = yield* list
+    const model = providers[ProviderV2.ID.githubCopilot].models["copilot-grok-4.6"]
+    expect(model).toBeDefined()
+    expect(model.api.npm).toBe("@ai-sdk/github-copilot")
+  }),
+  {
+    config: {
+      provider: {
+        "github-copilot": {
+          models: {
+            "copilot-grok-4.6": {
+              name: "Copilot Grok 4.6",
+              limit: { context: 128000, output: 64000 },
+            },
+          },
+        },
+      },
+    },
+  },
+)
+
 it.instance(
   "custom model inherits api.url from models.dev provider",
   Effect.gen(function* () {