diff --git a/src/agents/builtin-agents/model-resolution.ts b/src/agents/builtin-agents/model-resolution.ts
index dd5f32662..f692c9352 100644
--- a/src/agents/builtin-agents/model-resolution.ts
+++ b/src/agents/builtin-agents/model-resolution.ts
@@ -1,4 +1,5 @@
 import { resolveModelPipeline } from "../../shared"
+import { transformModelForProvider } from "../../shared/provider-model-id-transform"
 
 export function applyModelResolution(input: {
   uiSelectedModel?: string
@@ -20,8 +21,10 @@ export function getFirstFallbackModel(requirement?: {
 }) {
   const entry = requirement?.fallbackChain?.[0]
   if (!entry || entry.providers.length === 0) return undefined
+  const provider = entry.providers[0]
+  const transformedModel = transformModelForProvider(provider, entry.model)
   return {
-    model: `${entry.providers[0]}/${entry.model}`,
+    model: `${provider}/${transformedModel}`,
     provenance: "provider-fallback" as const,
     variant: entry.variant,
   }
diff --git a/src/cli/provider-model-id-transform.test.ts b/src/cli/provider-model-id-transform.test.ts
index 08317afb5..e13c7846a 100644
--- a/src/cli/provider-model-id-transform.test.ts
+++ b/src/cli/provider-model-id-transform.test.ts
@@ -63,6 +63,30 @@ describe("transformModelForProvider", () => {
 			// #then should transform to gemini-3-flash-preview
 			expect(result).toBe("gemini-3-flash-preview")
 		})
+
+		test("prevents double transformation of gemini-3-pro-preview", () => {
+			// #given github-copilot provider and gemini-3-pro-preview model (already transformed)
+			const provider = "github-copilot"
+			const model = "gemini-3-pro-preview"
+
+			// #when transformModelForProvider is called
+			const result = transformModelForProvider(provider, model)
+
+			// #then should NOT become gemini-3-pro-preview-preview
+			expect(result).toBe("gemini-3-pro-preview")
+		})
+
+		test("prevents double transformation of gemini-3-flash-preview", () => {
+			// #given github-copilot provider and gemini-3-flash-preview model (already transformed)
+			const provider = "github-copilot"
+			const model = "gemini-3-flash-preview"
+
+			// #when transformModelForProvider is called
+			const result = transformModelForProvider(provider, model)
+
+			// #then should NOT become gemini-3-flash-preview-preview
+			expect(result).toBe("gemini-3-flash-preview")
+		})
 	})
 
 	describe("google provider", () => {
diff --git a/src/shared/model-resolution-pipeline.ts b/src/shared/model-resolution-pipeline.ts
index 34d1c13b8..6b39f9d51 100644
--- a/src/shared/model-resolution-pipeline.ts
+++ b/src/shared/model-resolution-pipeline.ts
@@ -2,6 +2,7 @@ import { log } from "./logger"
 import * as connectedProvidersCache from "./connected-providers-cache"
 import { fuzzyMatchModel } from "./model-availability"
 import type { FallbackEntry } from "./model-requirements"
+import { transformModelForProvider } from "./provider-model-id-transform"
 
 export type ModelResolutionRequest = {
   intent?: {
@@ -85,10 +86,13 @@ export function resolveModelPipeline(
       if (parts.length >= 2) {
         const provider = parts[0]
         if (connectedProviders.includes(provider)) {
+          const modelName = parts.slice(1).join("/")
+          const transformedModel = `${provider}/${transformModelForProvider(provider, modelName)}`
           log("Model resolved via category default (connected provider)", {
-            model: normalizedCategoryDefault,
+            model: transformedModel,
+            original: normalizedCategoryDefault,
           })
-          return { model: normalizedCategoryDefault, provenance: "category-default", attempted }
+          return { model: transformedModel, provenance: "category-default", attempted }
         }
       }
     }
@@ -108,10 +112,11 @@ export function resolveModelPipeline(
         for (const entry of fallbackChain) {
           for (const provider of entry.providers) {
             if (connectedSet.has(provider)) {
-              const model = `${provider}/${entry.model}`
+              const transformedModelId = transformModelForProvider(provider, entry.model)
+              const model = `${provider}/${transformedModelId}`
               log("Model resolved via fallback chain (connected provider)", {
                 provider,
-                model: entry.model,
+                model: transformedModelId,
                 variant: entry.variant,
               })
               return {
diff --git a/src/shared/model-resolver.test.ts b/src/shared/model-resolver.test.ts
index 520c0c001..ea301a78a 100644
--- a/src/shared/model-resolver.test.ts
+++ b/src/shared/model-resolver.test.ts
@@ -543,7 +543,8 @@ describe("resolveModelWithFallback", () => {
       const result = resolveModelWithFallback(input)
 
       // then - should use github-copilot (second provider) since google not connected
-      expect(result!.model).toBe("github-copilot/gemini-3-pro")
+      // model name is transformed to preview variant for github-copilot provider
+      expect(result!.model).toBe("github-copilot/gemini-3-pro-preview")
       expect(result!.source).toBe("provider-fallback")
       cacheSpy.mockRestore()
     })
@@ -795,8 +796,82 @@ describe("resolveModelWithFallback", () => {
       // when
       const result = resolveModelWithFallback(input)
 
-      // then - should use categoryDefaultModel since google is connected
-      expect(result!.model).toBe("google/gemini-3-pro")
+      // then - should use transformed categoryDefaultModel since google is connected
+      expect(result!.model).toBe("google/gemini-3-pro-preview")
+      expect(result!.source).toBe("category-default")
+      cacheSpy.mockRestore()
+    })
+
+    test("transforms gemini-3-flash in categoryDefaultModel for google connected provider", () => {
+      // given - google connected, category default uses gemini-3-flash
+      const cacheSpy = spyOn(connectedProvidersCache, "readConnectedProvidersCache").mockReturnValue(["google"])
+      const input: ExtendedModelResolutionInput = {
+        categoryDefaultModel: "google/gemini-3-flash",
+        availableModels: new Set(),
+        systemDefaultModel: "anthropic/claude-sonnet-4-5",
+      }
+
+      // when
+      const result = resolveModelWithFallback(input)
+
+      // then - gemini-3-flash should be transformed to gemini-3-flash-preview
+      expect(result!.model).toBe("google/gemini-3-flash-preview")
+      expect(result!.source).toBe("category-default")
+      cacheSpy.mockRestore()
+    })
+
+    test("does not double-transform categoryDefaultModel already containing -preview", () => {
+      // given - category default already has -preview suffix
+      const cacheSpy = spyOn(connectedProvidersCache, "readConnectedProvidersCache").mockReturnValue(["google"])
+      const input: ExtendedModelResolutionInput = {
+        categoryDefaultModel: "google/gemini-3-pro-preview",
+        availableModels: new Set(),
+        systemDefaultModel: "anthropic/claude-sonnet-4-5",
+      }
+
+      // when
+      const result = resolveModelWithFallback(input)
+
+      // then - should NOT become gemini-3-pro-preview-preview
+      expect(result!.model).toBe("google/gemini-3-pro-preview")
+      expect(result!.source).toBe("category-default")
+      cacheSpy.mockRestore()
+    })
+
+    test("transforms gemini-3-pro in fallback chain for google connected provider", () => {
+      // given - google connected, fallback chain has gemini-3-pro
+      const cacheSpy = spyOn(connectedProvidersCache, "readConnectedProvidersCache").mockReturnValue(["google"])
+      const input: ExtendedModelResolutionInput = {
+        fallbackChain: [
+          { providers: ["google", "github-copilot"], model: "gemini-3-pro" },
+        ],
+        availableModels: new Set(),
+        systemDefaultModel: "anthropic/claude-sonnet-4-5",
+      }
+
+      // when
+      const result = resolveModelWithFallback(input)
+
+      // then - should transform to preview variant for google provider
+      expect(result!.model).toBe("google/gemini-3-pro-preview")
+      expect(result!.source).toBe("provider-fallback")
+      cacheSpy.mockRestore()
+    })
+
+    test("passes through non-gemini-3 models for google connected provider", () => {
+      // given - google connected, category default uses gemini-2.5-flash (no transform needed)
+      const cacheSpy = spyOn(connectedProvidersCache, "readConnectedProvidersCache").mockReturnValue(["google"])
+      const input: ExtendedModelResolutionInput = {
+        categoryDefaultModel: "google/gemini-2.5-flash",
+        availableModels: new Set(),
+        systemDefaultModel: "anthropic/claude-sonnet-4-5",
+      }
+
+      // when
+      const result = resolveModelWithFallback(input)
+
+      // then - should pass through unchanged
+      expect(result!.model).toBe("google/gemini-2.5-flash")
       expect(result!.source).toBe("category-default")
       cacheSpy.mockRestore()
     })
diff --git a/src/shared/provider-model-id-transform.ts b/src/shared/provider-model-id-transform.ts
index 0a326f126..5b8c810bb 100644
--- a/src/shared/provider-model-id-transform.ts
+++ b/src/shared/provider-model-id-transform.ts
@@ -6,16 +6,13 @@ export function transformModelForProvider(provider: string, model: string): stri
 			.replace("claude-sonnet-4-5", "claude-sonnet-4.5")
 			.replace("claude-haiku-4-5", "claude-haiku-4.5")
 			.replace("claude-sonnet-4", "claude-sonnet-4")
-			.replace("gemini-3-pro", "gemini-3-pro-preview")
-			.replace("gemini-3-flash", "gemini-3-flash-preview")
+			.replace(/gemini-3-pro(?!-)/g, "gemini-3-pro-preview")
+			.replace(/gemini-3-flash(?!-)/g, "gemini-3-flash-preview")
 	}
 	if (provider === "google") {
-		if (!model.endsWith("-preview")) {
-			return model
-				.replace("gemini-3-pro", "gemini-3-pro-preview")
-				.replace("gemini-3-flash", "gemini-3-flash-preview")
-		}
 		return model
+			.replace(/gemini-3-pro(?!-)/g, "gemini-3-pro-preview")
+			.replace(/gemini-3-flash(?!-)/g, "gemini-3-flash-preview")
 	}
 	return model
 }
diff --git a/src/tools/delegate-task/model-selection.ts b/src/tools/delegate-task/model-selection.ts
index 12987421e..188e3e374 100644
--- a/src/tools/delegate-task/model-selection.ts
+++ b/src/tools/delegate-task/model-selection.ts
@@ -1,5 +1,6 @@
 import type { FallbackEntry } from "../../shared/model-requirements"
 import { fuzzyMatchModel } from "../../shared/model-availability"
+import { transformModelForProvider } from "../../shared/provider-model-id-transform"
 
 function normalizeModel(model?: string): string | undefined {
   const trimmed = model?.trim()
@@ -38,7 +39,8 @@ export function resolveModelForDelegateTask(input: {
       const first = fallbackChain[0]
       const provider = first?.providers?.[0]
       if (provider) {
-        return { model: `${provider}/${first.model}`, variant: first.variant }
+        const transformedModelId = transformModelForProvider(provider, first.model)
+        return { model: `${provider}/${transformedModelId}`, variant: first.variant }
       }
     } else {
       for (const entry of fallbackChain) {