diff --git a/.changeset/add-claude-sonnet-4-6.md b/.changeset/add-claude-sonnet-4-6.md
new file mode 100644
index 00000000..e9547196
--- /dev/null
+++ b/.changeset/add-claude-sonnet-4-6.md
@@ -0,0 +1,5 @@
+---
+"@perstack/core": patch
+---
+
+feat: add claude-sonnet-4-6 to known models and update claude-opus-4-6 context window to 1M
diff --git a/packages/core/src/known-models/index.ts b/packages/core/src/known-models/index.ts
index 6c7bd557..7af934df 100644
--- a/packages/core/src/known-models/index.ts
+++ b/packages/core/src/known-models/index.ts
@@ -8,7 +8,7 @@ export const knownModels = [
       {
         name: "claude-opus-4-6",
         tier: "high" as const,
-        contextWindow: 200_000,
+        contextWindow: 1_000_000,
         maxOutputTokens: 128_000,
       },
       {
@@ -29,6 +29,12 @@ export const knownModels = [
         contextWindow: 200_000,
         maxOutputTokens: 32_000,
       },
+      {
+        name: "claude-sonnet-4-6",
+        tier: "middle" as const,
+        contextWindow: 1_000_000,
+        maxOutputTokens: 64_000,
+      },
       {
         name: "claude-sonnet-4-5",
         tier: "middle" as const,
@@ -51,13 +57,13 @@ export const knownModels = [
         name: "claude-haiku-4-5",
         tier: "low" as const,
         contextWindow: 200_000,
-        maxOutputTokens: 8_192,
+        maxOutputTokens: 64_000,
       },
       {
         name: "claude-3-5-haiku-latest",
         tier: "low" as const,
         contextWindow: 200_000,
-        maxOutputTokens: 8_192,
+        maxOutputTokens: 64_000,
       },
     ],
   },
diff --git a/packages/core/src/known-models/model-tiers.test.ts b/packages/core/src/known-models/model-tiers.test.ts
index d404f75d..b6d0f9ec 100644
--- a/packages/core/src/known-models/model-tiers.test.ts
+++ b/packages/core/src/known-models/model-tiers.test.ts
@@ -20,7 +20,7 @@ describe("@perstack/core: modelTierSchema", () => {
 describe("@perstack/core: resolveModelTier", () => {
   it("resolves anthropic tiers to the first matching model", () => {
     expect(resolveModelTier("anthropic", "low")).toBe("claude-haiku-4-5")
-    expect(resolveModelTier("anthropic", "middle")).toBe("claude-sonnet-4-5")
+    expect(resolveModelTier("anthropic", "middle")).toBe("claude-sonnet-4-6")
     expect(resolveModelTier("anthropic", "high")).toBe("claude-opus-4-6")
   })