diff --git a/src/hooks/runtime-fallback/fallback-state.ts b/src/hooks/runtime-fallback/fallback-state.ts
index 15348a21d6..a1eb122de5 100644
--- a/src/hooks/runtime-fallback/fallback-state.ts
+++ b/src/hooks/runtime-fallback/fallback-state.ts
@@ -2,6 +2,68 @@ import type { FallbackState, FallbackResult } from "./types"
 import { HOOK_NAME } from "./constants"
 import { log } from "../../shared/logger"
 import type { RuntimeFallbackConfig } from "../../config"
+import { parseModelString } from "../../tools/delegate-task/model-string-parser"
+
+function canonicalizeModelID(modelID: string): string {
+  const loweredModelID = modelID.toLowerCase()
+  const dottedModelID = loweredModelID.replace(/\./g, "-")
+
+  if (
+    dottedModelID.startsWith("claude-opus-") ||
+    dottedModelID.startsWith("claude-sonnet-") ||
+    dottedModelID.startsWith("claude-haiku-")
+  ) {
+    return dottedModelID
+      .replace(/-thinking$/i, "")
+      .replace(/-max$/i, "")
+      .replace(/-high$/i, "")
+  }
+
+  return modelID
+    .toLowerCase()
+    .replace(/\./g, "-")
+}
+
+function canonicalizeProviderFamily(providerID: string, modelID: string): string {
+  const canonicalModelID = canonicalizeModelID(modelID)
+
+  if (
+    canonicalModelID.startsWith("claude-opus-") ||
+    canonicalModelID.startsWith("claude-sonnet-") ||
+    canonicalModelID.startsWith("claude-haiku-")
+  ) {
+    return "anthropic-compatible-claude"
+  }
+
+  return providerID.toLowerCase()
+}
+
+function parseCanonicalModel(model: string): { providerID: string; modelID: string } | undefined {
+  const parsed = parseModelString(model)
+  if (!parsed?.providerID || !parsed.modelID) return undefined
+
+  const canonicalModelID = canonicalizeModelID(parsed.modelID)
+  const variant = parsed.variant?.toLowerCase()
+
+  return {
+    providerID: canonicalizeProviderFamily(parsed.providerID, parsed.modelID),
+    modelID: variant ? `${canonicalModelID}::${variant}` : canonicalModelID,
+  }
+}
+
+function isEquivalentModel(candidate: string, current: string): boolean {
+  const parsedCandidate = parseCanonicalModel(candidate)
+  const parsedCurrent = parseCanonicalModel(current)
+
+  if (!parsedCandidate || !parsedCurrent) {
+    return candidate.toLowerCase() === current.toLowerCase()
+  }
+
+  return (
+    parsedCandidate.providerID === parsedCurrent.providerID &&
+    parsedCandidate.modelID === parsedCurrent.modelID
+  )
+}
 
 export function createFallbackState(originalModel: string): FallbackState {
   return {
@@ -28,6 +90,15 @@ export function findNextAvailableFallback(
 ): string | undefined {
   for (let i = state.fallbackIndex + 1; i < fallbackModels.length; i++) {
     const candidate = fallbackModels[i]
+    if (isEquivalentModel(candidate, state.currentModel)) {
+      log(`[${HOOK_NAME}] Skipping equivalent fallback model`, {
+        model: candidate,
+        currentModel: state.currentModel,
+        index: i,
+      })
+      continue
+    }
+
     if (!isModelInCooldown(candidate, state, cooldownSeconds)) {
       return candidate
     }
diff --git a/src/hooks/runtime-fallback/index.test.ts b/src/hooks/runtime-fallback/index.test.ts
index 3956d26c81..e6401f86c0 100644
--- a/src/hooks/runtime-fallback/index.test.ts
+++ b/src/hooks/runtime-fallback/index.test.ts
@@ -1245,7 +1245,10 @@ describe("runtime-fallback", () => {
 
       expect(retriedModels.length).toBeGreaterThanOrEqual(2)
       expect(retriedModels[0]).toBe("github-copilot/claude-opus-4.6")
-      expect(retriedModels[1]).toBe("anthropic/claude-opus-4-6")
+      expect(retriedModels[1]).toBe("openai/gpt-5.4")
+
+      const equivalentSkipLog = logCalls.find((c) => c.msg.includes("Skipping equivalent fallback model"))
+      expect(equivalentSkipLog).toBeDefined()
 
       void sessionErrorPromise
     })
@@ -1314,7 +1317,7 @@ describe("runtime-fallback", () => {
       await new Promise((resolve) => setTimeout(resolve, 50))
 
       expect(retriedModels).toContain("github-copilot/claude-opus-4.6")
-      expect(retriedModels).toContain("anthropic/claude-opus-4-6")
+      expect(retriedModels).toContain("openai/gpt-5.4")
       expect(abortCalls.some((call) => call.path?.id === sessionID)).toBe(true)
 
       const timeoutLog = logCalls.find((c) => c.msg.includes("Session fallback timeout reached"))
@@ -1392,7 +1395,7 @@ describe("runtime-fallback", () => {
       await new Promise((resolve) => setTimeout(resolve, 50))
 
       expect(retriedModels).toContain("github-copilot/claude-opus-4.6")
-      expect(retriedModels).toContain("anthropic/claude-opus-4-6")
+      expect(retriedModels).toContain("openai/gpt-5.4")
     })
 
     test("should abort in-flight fallback request before advancing on timeout", async () => {
@@ -1466,7 +1469,7 @@ describe("runtime-fallback", () => {
 
       expect(abortCalls.some((call) => call.path?.id === sessionID)).toBe(true)
       expect(retriedModels).toContain("github-copilot/claude-opus-4.6")
-      expect(retriedModels).toContain("anthropic/claude-opus-4-6")
+      expect(retriedModels).toContain("openai/gpt-5.4")
 
       void sessionErrorPromise
     })
@@ -2385,7 +2388,10 @@ describe("runtime-fallback", () => {
         }),
         {
           config: createMockConfig({ notify_on_fallback: false }),
-          pluginConfig: createMockPluginConfigWithAgentFallback("prometheus", ["github-copilot/claude-opus-4.6"]),
+          pluginConfig: createMockPluginConfigWithAgentFallback("prometheus", [
+            "github-copilot/claude-opus-4.6",
+            "openai/gpt-5.4",
+          ]),
         },
       )
       const sessionID = "test-preserve-agent-on-retry"
@@ -2405,7 +2411,7 @@ describe("runtime-fallback", () => {
       expect(promptCalls.length).toBe(1)
       const callBody = promptCalls[0]?.body as Record<string, unknown>
       expect(callBody?.agent).toBe("prometheus")
-      expect(callBody?.model).toEqual({ providerID: "github-copilot", modelID: "claude-opus-4.6" })
+      expect(callBody?.model).toEqual({ providerID: "openai", modelID: "gpt-5.4" })
     })
   })