diff --git a/.changeset/max-reasoning-effort.md b/.changeset/max-reasoning-effort.md
new file mode 100644
index 000000000..842673e4c
--- /dev/null
+++ b/.changeset/max-reasoning-effort.md
@@ -0,0 +1,5 @@
+---
+'@bradygaster/squad-sdk': patch
+---
+
+Add `"max"` as a valid `SquadReasoningEffort` level to match the Copilot SDK 1.0.9 addition of `ReasoningEffort = "max"`. Unblocks Dependabot PR #1671.
diff --git a/packages/squad-sdk/src/adapter/types.ts b/packages/squad-sdk/src/adapter/types.ts
index 7a2b14657..5d5e37a55 100644
--- a/packages/squad-sdk/src/adapter/types.ts
+++ b/packages/squad-sdk/src/adapter/types.ts
@@ -766,7 +766,7 @@ export interface SquadInfiniteSessionConfig {
  * re-declaring the union inline. The runtime list lives in config/models.ts as
  * `VALID_REASONING_EFFORTS` (kept in sync via `satisfies`).
  */
-export type SquadReasoningEffort = "low" | "medium" | "high" | "xhigh";
+export type SquadReasoningEffort = "low" | "medium" | "high" | "xhigh" | "max";
 
 /**
  * Valid context tiers (context-window sizes) for models that support them.
diff --git a/packages/squad-sdk/src/config/models.ts b/packages/squad-sdk/src/config/models.ts
index 705fa6e3a..a6c4a6e5f 100644
--- a/packages/squad-sdk/src/config/models.ts
+++ b/packages/squad-sdk/src/config/models.ts
@@ -817,7 +817,7 @@ export function writeAgentModelOverrides(
  * Canonical runtime list — import this instead of duplicating. The `satisfies`
  * clause keeps it in lock-step with the canonical {@link SquadReasoningEffort} type.
  */
-export const VALID_REASONING_EFFORTS = ['low', 'medium', 'high', 'xhigh'] as const satisfies readonly SquadReasoningEffort[];
+export const VALID_REASONING_EFFORTS = ['low', 'medium', 'high', 'xhigh', 'max'] as const satisfies readonly SquadReasoningEffort[];
 /** Canonical reasoning-effort union (alias of {@link SquadReasoningEffort}). */
 export type ValidReasoningEffort = SquadReasoningEffort;
 const VALID_REASONING_EFFORTS_WITH_AUTO: readonly string[] = [...VALID_REASONING_EFFORTS, 'auto'];
diff --git a/test/model-preference.test.ts b/test/model-preference.test.ts
index 60a69526f..691791b56 100644
--- a/test/model-preference.test.ts
+++ b/test/model-preference.test.ts
@@ -463,6 +463,13 @@ describe('writeReasoningEffort', () => {
     const raw = JSON.parse(readFileSync(join(squadDir, 'config.json'), 'utf-8'));
     expect(raw).not.toHaveProperty('defaultReasoningEffort');
   });
+
+  it('accepts max as a valid effort level', () => {
+    writeReasoningEffort(squadDir, 'max');
+    const raw = JSON.parse(readFileSync(join(squadDir, 'config.json'), 'utf-8'));
+    expect(raw.defaultReasoningEffort).toBe('max');
+    expect(readReasoningEffort(squadDir)).toBe('max');
+  });
 });
 
 // ============================================================================
@@ -641,6 +648,16 @@ describe('clampReasoningEffort', () => {
   it('treats max and xhigh as equivalent', () => {
     // xhigh requested, model supports max
     expect(clampReasoningEffort('xhigh', ['low', 'medium', 'high', 'max'])).toBe('xhigh');
+    // max requested, model supports xhigh
+    expect(clampReasoningEffort('max', ['low', 'medium', 'high', 'xhigh'])).toBe('xhigh');
+  });
+
+  it('passes through max when model directly supports max', () => {
+    expect(clampReasoningEffort('max', ['low', 'medium', 'high', 'max'])).toBe('max');
+  });
+
+  it('clamps max to xhigh for models that use that name at the top tier', () => {
+    expect(clampReasoningEffort('max', ['low', 'medium', 'high', 'xhigh'])).toBe('xhigh');
   });
 
   it('returns undefined for unrecognized effort value', () => {