diff --git a/src/common/utils/ai/modelDisplay.test.ts b/src/common/utils/ai/modelDisplay.test.ts
index 0aa441b440..0480ff7958 100644
--- a/src/common/utils/ai/modelDisplay.test.ts
+++ b/src/common/utils/ai/modelDisplay.test.ts
@@ -29,6 +29,11 @@ describe("formatModelDisplayName", () => {
       expect(formatModelDisplayName("claude-fable-5")).toBe("Fable 5");
       expect(formatModelDisplayName("claude-mythos-5")).toBe("Mythos 5");
     });
+
+    test("formats pre-release Opus 5.1 / Fable 5.1 ids", () => {
+      expect(formatModelDisplayName("claude-opus-5-1")).toBe("Opus 5.1");
+      expect(formatModelDisplayName("claude-fable-5-1")).toBe("Fable 5.1");
+    });
   });
 
   describe("GPT models", () => {
diff --git a/src/common/utils/ai/models.test.ts b/src/common/utils/ai/models.test.ts
index f4eab11f21..ec60f24e7e 100644
--- a/src/common/utils/ai/models.test.ts
+++ b/src/common/utils/ai/models.test.ts
@@ -167,6 +167,17 @@ describe("Anthropic 1M context classification", () => {
     expect(hasNative1MContext("anthropic:claude-sonnet-5")).toBe(true);
   });
 
+  it("treats pre-release Opus 5.1 / Fable 5.1 as native 1M models", () => {
+    // Seeded from their direct predecessors (Opus 5 / Fable 5); confirm at release.
+    expect(getAnthropic1MContextMode("anthropic:claude-opus-5-1")).toBe("native");
+    expect(getAnthropic1MContextMode("anthropic:claude-opus-5-1-20260901")).toBe("native");
+    expect(getAnthropic1MContextMode("anthropic:claude-fable-5-1")).toBe("native");
+    expect(getAnthropic1MContextMode("mux-gateway:anthropic/claude-fable-5-1")).toBe("native");
+    expect(hasNative1MContext("anthropic:claude-opus-5-1")).toBe(true);
+    expect(supports1MContext("anthropic:claude-opus-5-1")).toBe(false);
+    expect(supports1MContext("anthropic:claude-fable-5-1")).toBe(false);
+  });
+
   it("treats Mythos-class Fable 5 / Mythos 5 as native 1M models", () => {
     expect(getAnthropic1MContextMode("anthropic:claude-fable-5")).toBe("native");
     expect(getAnthropic1MContextMode("anthropic:claude-mythos-5")).toBe("native");
diff --git a/src/common/utils/ai/models.ts b/src/common/utils/ai/models.ts
index f4b4d614ea..790fbee26c 100644
--- a/src/common/utils/ai/models.ts
+++ b/src/common/utils/ai/models.ts
@@ -180,6 +180,10 @@ const ANTHROPIC_NATIVE_1M_PATTERNS = [
   // Mythos-class models (Fable 5 / Mythos 5) ship 1M context as standard metadata.
   new RegExp(`^claude-fable-5${OPTIONAL_VERSION_SUFFIX}$`, "i"),
   new RegExp(`^claude-mythos-5${OPTIONAL_VERSION_SUFFIX}$`, "i"),
+  // Pre-release Fable 5.1 / Opus 5.1: seeded to keep their predecessors' native 1M
+  // context; confirm against the announcement before release.
+  new RegExp(`^claude-fable-5-1${OPTIONAL_VERSION_SUFFIX}$`, "i"),
+  new RegExp(`^claude-opus-5-1${OPTIONAL_VERSION_SUFFIX}$`, "i"),
   new RegExp(`^claude-opus-5${OPTIONAL_VERSION_SUFFIX}$`, "i"),
   new RegExp(`^claude-opus-4-8${OPTIONAL_VERSION_SUFFIX}$`, "i"),
   new RegExp(`^claude-opus-4-7${OPTIONAL_VERSION_SUFFIX}$`, "i"),
diff --git a/src/common/utils/ai/providerOptions.test.ts b/src/common/utils/ai/providerOptions.test.ts
index 8467dbe0ca..7ca18e1e1b 100644
--- a/src/common/utils/ai/providerOptions.test.ts
+++ b/src/common/utils/ai/providerOptions.test.ts
@@ -139,7 +139,14 @@ describe("buildProviderOptions - Anthropic", () => {
   // Native-xhigh models (Opus 4.7+ / Sonnet 5+): xhigh is a distinct native
   // effort and adaptive thinking requires `display: "summarized"` to return
   // thinking content.
-  for (const model of ["claude-opus-4-7", "claude-opus-5", "claude-sonnet-5"] as const) {
+  // claude-opus-5-1 is the pre-release Opus 5.1 id (unconfirmed): it must inherit
+  // the same native-xhigh wire transforms as its predecessor.
+  for (const model of [
+    "claude-opus-4-7",
+    "claude-opus-5",
+    "claude-opus-5-1",
+    "claude-sonnet-5",
+  ] as const) {
     describe(`${model} (native xhigh effort + summarized display)`, () => {
       for (const { thinking, expectedThinking, effort } of [
         {
diff --git a/src/common/utils/thinking/policy.test.ts b/src/common/utils/thinking/policy.test.ts
index baa3862272..e479a664a4 100644
--- a/src/common/utils/thinking/policy.test.ts
+++ b/src/common/utils/thinking/policy.test.ts
@@ -431,6 +431,15 @@ describe("getThinkingPolicyForModel", () => {
       "xhigh",
       "max",
     ]);
+    // Pre-release Opus 5.1 (unconfirmed id) — inherits the forward-compatible Opus policy.
+    expect(getThinkingPolicyForModel("anthropic:claude-opus-5-1")).toEqual([
+      "off",
+      "low",
+      "medium",
+      "high",
+      "xhigh",
+      "max",
+    ]);
   });
 
   test("excludes 'off' for Mythos-class Fable 5 / Mythos 5 (API rejects disabled thinking)", () => {
@@ -450,6 +459,14 @@ describe("getThinkingPolicyForModel", () => {
       "xhigh",
       "max",
     ]);
+    // Pre-release Fable 5.1 (unconfirmed id) — inherits the Mythos-class no-"off" policy.
+    expect(getThinkingPolicyForModel("anthropic:claude-fable-5-1")).toEqual([
+      "low",
+      "medium",
+      "high",
+      "xhigh",
+      "max",
+    ]);
   });
 
   test("clamps 'off' up to 'low' for Mythos-class models", () => {
diff --git a/src/common/utils/tokens/models-extra.ts b/src/common/utils/tokens/models-extra.ts
index e28a1bc340..2741aaff5b 100644
--- a/src/common/utils/tokens/models-extra.ts
+++ b/src/common/utils/tokens/models-extra.ts
@@ -135,6 +135,27 @@ export const modelsExtra: Record<string, ModelData> = {
     supports_pdf_input: true,
   },
 
+  // Claude Fable 5.1 - PRE-RELEASE, NOT YET ANNOUNCED (unconfirmed id).
+  // Every value below is seeded from the direct predecessor `claude-fable-5`
+  // ($10/M input, $50/M output, cache write 1.25x input, cache read 0.1x input,
+  // native 1M context, 128K max output) and must be confirmed against
+  // Anthropic's announcement before release.
+  "claude-fable-5-1": {
+    max_input_tokens: 1000000,
+    max_output_tokens: 128000,
+    input_cost_per_token: 0.00001, // $10 per million input tokens (seeded from Fable 5)
+    output_cost_per_token: 0.00005, // $50 per million output tokens (seeded from Fable 5)
+    cache_creation_input_token_cost: 0.0000125, // $12.50 per million tokens (1.25x input)
+    cache_read_input_token_cost: 0.000001, // $1.00 per million tokens (0.1x input)
+    litellm_provider: "anthropic",
+    mode: "chat",
+    supports_function_calling: true,
+    supports_vision: true,
+    supports_pdf_input: true,
+    supports_reasoning: true,
+    supports_response_schema: true,
+  },
+
   // Claude Fable 5 / Mythos 5 - Released June 9, 2026
   // Mythos-class model (a tier above Opus). Fable 5 (`claude-fable-5`) is the
   // generally-available variant with safeguards; Mythos 5 (`claude-mythos-5`) is the same
@@ -175,6 +196,27 @@ export const modelsExtra: Record<string, ModelData> = {
     supports_response_schema: true,
   },
 
+  // Claude Opus 5.1 - PRE-RELEASE, NOT YET ANNOUNCED (unconfirmed id).
+  // Every value below is seeded from the direct predecessor `claude-opus-5`
+  // ($5/M input, $25/M output, cache write $6.25, cache read $0.50, native 1M
+  // context, 128K max output) and must be confirmed against Anthropic's
+  // announcement before release.
+  "claude-opus-5-1": {
+    max_input_tokens: 1000000,
+    max_output_tokens: 128000,
+    input_cost_per_token: 0.000005, // $5 per million input tokens (seeded from Opus 5)
+    output_cost_per_token: 0.000025, // $25 per million output tokens (seeded from Opus 5)
+    cache_creation_input_token_cost: 0.00000625, // $6.25 per million tokens
+    cache_read_input_token_cost: 0.0000005, // $0.50 per million tokens
+    litellm_provider: "anthropic",
+    mode: "chat",
+    supports_function_calling: true,
+    supports_vision: true,
+    supports_pdf_input: true,
+    supports_reasoning: true,
+    supports_response_schema: true,
+  },
+
   // Claude Opus 5 - Released July 24, 2026
   // Same pricing/shape as Opus 4.8: $5/M input, $25/M output, native 1M context
   // (both default and maximum), 128K max output, full effort ladder with native
diff --git a/src/common/utils/tools/tools.test.ts b/src/common/utils/tools/tools.test.ts
index fd5fb8fcf7..b098c3b2e8 100644
--- a/src/common/utils/tools/tools.test.ts
+++ b/src/common/utils/tools/tools.test.ts
@@ -71,6 +71,9 @@ describe("supportsAnthropicNativeWebFetch", () => {
     ["claude-opus-5", true],
     ["claude-fable-5", true],
     ["claude-mythos-5", true],
+    // Pre-release 5.1 ids (unconfirmed) parse as major=5 / minor=1 and qualify.
+    ["claude-opus-5-1", true],
+    ["claude-fable-5-1", true],
     // Two-segment IDs at/after the 4.6 cutoff.
     ["claude-sonnet-4-6", true],
     ["claude-opus-4-6", true],