diff --git a/packages/contracts/src/model.ts b/packages/contracts/src/model.ts
index 8027c90799dbc..87990e7f542f7 100644
--- a/packages/contracts/src/model.ts
+++ b/packages/contracts/src/model.ts
@@ -160,7 +160,7 @@ export const DEFAULT_TEXT_GENERATION_MODEL_BY_PROVIDER: Partial<
   [ProviderDriverKind.make("antigravity")]: ANTIGRAVITY_DEFAULT_MODEL,
   [CLAUDE_DRIVER_KIND]: "claude-haiku-5-5",
   [CURSOR_DRIVER_KIND]: "composer-2",
-  [OPENCODE_DRIVER_KIND]: "openai/gpt-5",
+  [OPENCODE_DRIVER_KIND]: "opencode/big-pickle",
 };
 
 export const MODEL_SLUG_ALIASES_BY_PROVIDER: Partial<
diff --git a/packages/provider-opencode/src/server/textGeneration.ts b/packages/provider-opencode/src/server/textGeneration.ts
index 11d6c19fba2c2..eed819e44d62c 100644
--- a/packages/provider-opencode/src/server/textGeneration.ts
+++ b/packages/provider-opencode/src/server/textGeneration.ts
@@ -190,7 +190,11 @@ export const makeOpenCodeTextGeneration = Effect.fn("makeOpenCodeTextGeneration"
             client.session.create(
               {
                 title: `T3 Code ${input.operation}`,
-                permission: [{ permission: "*", pattern: "*", action: "deny" }],
+                // OpenCode Zen refuses free-model requests that carry no tools, so keep read.
+                permission: [
+                  { permission: "*", pattern: "*", action: "deny" },
+                  { permission: "read", pattern: "*", action: "allow" },
+                ],
               },
               { signal },
             ),
diff --git a/packages/shared/src/serverSettings.test.ts b/packages/shared/src/serverSettings.test.ts
index 26cbfb3df9d59..a897f3d427a34 100644
--- a/packages/shared/src/serverSettings.test.ts
+++ b/packages/shared/src/serverSettings.test.ts
@@ -32,6 +32,12 @@ const decodeServerSettingsPatch = Schema.decodeUnknownSync(ServerSettingsPatch);
 const FOLDED_SERVER_SETTINGS = { ...DEFAULT_SERVER_SETTINGS, projectSettingsFolded: true };
 
 describe("fallbackTextGenerationModelSelection", () => {
+  it("uses Big Pickle when only OpenCode is enabled", () => {
+    expect(
+      fallbackTextGenerationModelSelection({}, (instanceId) => instanceId === "opencode"),
+    ).toEqual({ instanceId: "opencode", model: "opencode/big-pickle" });
+  });
+
   it("replaces and clears the fallback without carrying model options", () => {
     const fallbackModelSelection = { instanceId: ProviderInstanceId.make("codex"), model: "new" };
     const settings = applyServerSettingsPatch(