diff --git a/src/lib/sdk-invoke.ts b/src/lib/sdk-invoke.ts
index e1c365cc9..e9137a3d3 100644
--- a/src/lib/sdk-invoke.ts
+++ b/src/lib/sdk-invoke.ts
@@ -59,17 +59,43 @@ function buildIsolatedEnv(
 /** Type alias for command handler functions loaded from Stricli's route tree. */
 type CommandHandler = (...args: unknown[]) => unknown;
 
-/** Cached command loaders, keyed by joined path (e.g., "org.list") */
-const commandCache = new Map<string, () => Promise<CommandHandler>>();
+/**
+ * Stricli flag definition shape — subset needed for default application.
+ *
+ * The SDK invoke path bypasses Stricli's `buildArgumentScanner`, so parsed
+ * flags with defaults never have their `parse` function called on the default
+ * string. We capture the flag definitions here so {@link applyFlagDefaults}
+ * can replicate that behavior at invocation time.
+ */
+export type FlagDef = {
+  kind: string;
+  default?: unknown;
+  optional?: boolean;
+  parse?: (value: string) => unknown;
+  variadic?: boolean;
+};
+
+/** Resolved command: handler function + flag definitions for default application. */
+type ResolvedCommand = {
+  handler: CommandHandler;
+  flagDefs: Record<string, FlagDef>;
+};
+
+/** Cached command entries, keyed by joined path (e.g., "org.list"). */
+const commandCache = new Map<
+  string,
+  { loader: () => Promise<CommandHandler>; flagDefs: Record<string, FlagDef> }
+>();
 
 /**
  * Resolve a command from the route tree by path segments.
+ * Returns both the handler function and the command's flag definitions.
  * Result is cached — route tree is only walked once per command.
  */
-async function resolveCommand(path: string[]): Promise<CommandHandler> {
+async function resolveCommand(path: string[]): Promise<ResolvedCommand> {
   const key = path.join(".");
-  let loaderFn = commandCache.get(key);
-  if (!loaderFn) {
+  let cached = commandCache.get(key);
+  if (!cached) {
     const { routes } = await import("../app.js");
     // Walk route tree: routes → sub-route → command
     // biome-ignore lint/suspicious/noExplicitAny: Stricli's RoutingTarget union requires runtime duck-typing
@@ -80,16 +106,87 @@ async function resolveCommand(path: string[]): Promise<CommandHandler> {
         throw new Error(`SDK: command not found: ${path.join(" ")}`);
       }
     }
-    // target is now a Command — cache its loader
+    // target is now a Command — extract flag definitions and cache loader
     const command = target;
-    loaderFn = () =>
-      command.loader().then(
-        // biome-ignore lint/suspicious/noExplicitAny: Stricli CommandModule shape has a default export
-        (m: any) => (typeof m === "function" ? m : m.default)
-      );
-    commandCache.set(key, loaderFn);
+    const flagDefs: Record<string, FlagDef> = command.parameters?.flags ?? {};
+    cached = {
+      loader: () =>
+        command.loader().then(
+          // biome-ignore lint/suspicious/noExplicitAny: Stricli CommandModule shape has a default export
+          (m: any) => (typeof m === "function" ? m : m.default)
+        ),
+      flagDefs,
+    };
+    commandCache.set(key, cached);
+  }
+  return { handler: await cached.loader(), flagDefs: cached.flagDefs };
+}
+
+/**
+ * Resolve the default value for a single flag definition.
+ *
+ * For `kind: "parsed"` flags with a string default, calls `flag.parse(flag.default)`
+ * to replicate Stricli's `parseInput` behavior. For all other flag kinds (boolean,
+ * enum, counter), returns the raw default value.
+ *
+ * @returns The resolved default, or `undefined` if no default is defined.
+ * @throws Re-throws if `flag.parse(flag.default)` fails — a parse function
+ *   that rejects its own default is a command definition bug, not a runtime error.
+ */
+function resolveFlagDefault(def: FlagDef): unknown {
+  if (!("default" in def) || def.default === undefined) {
+    return;
+  }
+  if (
+    def.kind === "parsed" &&
+    typeof def.default === "string" &&
+    typeof def.parse === "function"
+  ) {
+    return def.parse(def.default);
   }
-  return loaderFn();
+  return def.default;
+}
+
+/**
+ * Apply Stricli flag defaults for any missing or undefined flag values.
+ *
+ * The SDK invoke path bypasses Stricli's `buildArgumentScanner`, so parsed
+ * flags with defaults (e.g., `period: { kind: "parsed", parse: parsePeriod,
+ * default: "7d" }`) never have their `parse` function called on the default
+ * string. This function replicates that behavior:
+ *
+ * - For `kind: "parsed"` flags with a string `default`, calls `flag.parse(flag.default)`
+ *   (same as Stricli's `parseInput` path in `parseInputsForFlag`).
+ * - For `kind: "boolean"` / `kind: "enum"` flags with a `default`, uses the raw value.
+ * - Skips flags already set (non-`undefined`) by the caller.
+ *
+ * @param flags - The flags object from the SDK caller (may have `undefined` values).
+ * @param flagDefs - The command's Stricli flag definitions.
+ * @returns A new flags object with defaults applied.
+ */
+export function applyFlagDefaults(
+  flags: Record<string, unknown>,
+  flagDefs: Record<string, FlagDef>
+): Record<string, unknown> {
+  const result: Record<string, unknown> = {};
+  // Copy caller-provided flags, skipping undefined values so they
+  // don't shadow the defaults we're about to apply.
+  for (const [key, value] of Object.entries(flags)) {
+    if (value !== undefined) {
+      result[key] = value;
+    }
+  }
+  // Apply defaults for any flag not already set by the caller
+  for (const [name, def] of Object.entries(flagDefs)) {
+    if (name in result) {
+      continue;
+    }
+    const resolved = resolveFlagDefault(def);
+    if (resolved !== undefined) {
+      result[name] = resolved;
+    }
+  }
+  return result;
 }
 
 // biome-ignore lint/suspicious/noControlCharactersInRegex: ANSI escape sequences use ESC (0x1b)
@@ -412,26 +509,32 @@ export function buildInvoker(options?: SentryOptions) {
   ): Promise<T> | AsyncIterable<T> {
     if (meta?.streaming) {
       return executeWithStream<T>(options, async (ctx, span) => {
-        const func = await resolveCommand(commandPath);
+        const { handler, flagDefs } = await resolveCommand(commandPath);
         if (span) {
           const { setCommandSpanName } = await import("./telemetry.js");
           setCommandSpanName(span, commandPath.join("."));
         }
-        await func.call(
+        const resolvedFlags = applyFlagDefaults(flags, flagDefs);
+        await handler.call(
           ctx.context,
-          { ...flags, json: true },
+          { ...resolvedFlags, json: true },
           ...positionalArgs
         );
       });
     }
 
     return executeWithCapture<T>(options, async (ctx, span) => {
-      const func = await resolveCommand(commandPath);
+      const { handler, flagDefs } = await resolveCommand(commandPath);
       if (span) {
         const { setCommandSpanName } = await import("./telemetry.js");
         setCommandSpanName(span, commandPath.join("."));
       }
-      await func.call(ctx.context, { ...flags, json: true }, ...positionalArgs);
+      const resolvedFlags = applyFlagDefaults(flags, flagDefs);
+      await handler.call(
+        ctx.context,
+        { ...resolvedFlags, json: true },
+        ...positionalArgs
+      );
     });
   };
 }
diff --git a/test/lib/sdk-invoke.test.ts b/test/lib/sdk-invoke.test.ts
new file mode 100644
index 000000000..55c7d0a78
--- /dev/null
+++ b/test/lib/sdk-invoke.test.ts
@@ -0,0 +1,183 @@
+/**
+ * Unit tests for the SDK invoke layer.
+ *
+ * Focuses on `applyFlagDefaults` which replicates Stricli's default
+ * application for the SDK direct-invoke path (bypasses Stricli parsing).
+ */
+
+import { describe, expect, test } from "vitest";
+import { applyFlagDefaults, type FlagDef } from "../../src/lib/sdk-invoke.js";
+
+// ---------------------------------------------------------------------------
+// applyFlagDefaults — parsed flags with defaults
+// ---------------------------------------------------------------------------
+
+describe("applyFlagDefaults: parsed flags with defaults", () => {
+  test("calls parse on string default when flag is missing", () => {
+    const flagDefs: Record<string, FlagDef> = {
+      period: {
+        kind: "parsed",
+        default: "7d",
+        parse: (v: string) => ({ type: "relative", period: v }),
+      },
+    };
+    const result = applyFlagDefaults({}, flagDefs);
+    expect(result.period).toEqual({ type: "relative", period: "7d" });
+  });
+
+  test("calls parse on string default when flag value is undefined", () => {
+    const flagDefs: Record<string, FlagDef> = {
+      period: {
+        kind: "parsed",
+        default: "90d",
+        parse: (v: string) => ({ type: "relative", period: v }),
+      },
+    };
+    const result = applyFlagDefaults({ period: undefined }, flagDefs);
+    expect(result.period).toEqual({ type: "relative", period: "90d" });
+  });
+
+  test("preserves caller-provided value over default", () => {
+    const flagDefs: Record<string, FlagDef> = {
+      period: {
+        kind: "parsed",
+        default: "7d",
+        parse: (v: string) => ({ type: "relative", period: v }),
+      },
+    };
+    const callerValue = { type: "relative", period: "24h" };
+    const result = applyFlagDefaults({ period: callerValue }, flagDefs);
+    expect(result.period).toBe(callerValue);
+  });
+
+  test("handles parse function that returns a number", () => {
+    const flagDefs: Record<string, FlagDef> = {
+      limit: {
+        kind: "parsed",
+        default: "25",
+        parse: (v: string) => Number(v),
+      },
+    };
+    const result = applyFlagDefaults({}, flagDefs);
+    expect(result.limit).toBe(25);
+  });
+
+  test("re-throws if parse function rejects its own default", () => {
+    const flagDefs: Record<string, FlagDef> = {
+      period: {
+        kind: "parsed",
+        default: "invalid",
+        parse: () => {
+          throw new Error("parse error");
+        },
+      },
+    };
+    expect(() => applyFlagDefaults({}, flagDefs)).toThrow("parse error");
+  });
+});
+
+// ---------------------------------------------------------------------------
+// applyFlagDefaults — boolean flags
+// ---------------------------------------------------------------------------
+
+describe("applyFlagDefaults: boolean flags", () => {
+  test("applies raw boolean default", () => {
+    const flagDefs: Record<string, FlagDef> = {
+      json: { kind: "boolean", default: false },
+      fresh: { kind: "boolean", default: false },
+    };
+    const result = applyFlagDefaults({}, flagDefs);
+    expect(result.json).toBe(false);
+    expect(result.fresh).toBe(false);
+  });
+
+  test("preserves caller-provided boolean over default", () => {
+    const flagDefs: Record<string, FlagDef> = {
+      fresh: { kind: "boolean", default: false },
+    };
+    const result = applyFlagDefaults({ fresh: true }, flagDefs);
+    expect(result.fresh).toBe(true);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// applyFlagDefaults — enum flags
+// ---------------------------------------------------------------------------
+
+describe("applyFlagDefaults: enum flags", () => {
+  test("applies raw enum default", () => {
+    const flagDefs: Record<string, FlagDef> = {
+      sort: { kind: "enum", default: "date" },
+    };
+    const result = applyFlagDefaults({}, flagDefs);
+    expect(result.sort).toBe("date");
+  });
+});
+
+// ---------------------------------------------------------------------------
+// applyFlagDefaults — optional flags without defaults
+// ---------------------------------------------------------------------------
+
+describe("applyFlagDefaults: optional flags without defaults", () => {
+  test("does not inject value for optional flag with no default", () => {
+    const flagDefs: Record<string, FlagDef> = {
+      query: { kind: "parsed", optional: true },
+    };
+    const result = applyFlagDefaults({}, flagDefs);
+    expect("query" in result).toBe(false);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// applyFlagDefaults — strips undefined, preserves other falsy values
+// ---------------------------------------------------------------------------
+
+describe("applyFlagDefaults: undefined stripping", () => {
+  test("strips undefined values from input flags", () => {
+    const flagDefs: Record<string, FlagDef> = {};
+    const result = applyFlagDefaults(
+      { a: undefined, b: null, c: 0, d: "", e: false },
+      flagDefs
+    );
+    expect("a" in result).toBe(false);
+    expect(result.b).toBeNull();
+    expect(result.c).toBe(0);
+    expect(result.d).toBe("");
+    expect(result.e).toBe(false);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// applyFlagDefaults — multiple flags combined
+// ---------------------------------------------------------------------------
+
+describe("applyFlagDefaults: combined scenario", () => {
+  test("applies defaults for missing flags while preserving provided ones", () => {
+    const flagDefs: Record<string, FlagDef> = {
+      period: {
+        kind: "parsed",
+        default: "7d",
+        parse: (v: string) => ({ type: "relative", period: v }),
+      },
+      limit: {
+        kind: "parsed",
+        default: "25",
+        parse: (v: string) => Number(v),
+      },
+      sort: { kind: "enum", default: "date" },
+      fresh: { kind: "boolean", default: false },
+      query: { kind: "parsed", optional: true },
+    };
+    const result = applyFlagDefaults({ limit: 50, query: undefined }, flagDefs);
+    // period: default applied via parse
+    expect(result.period).toEqual({ type: "relative", period: "7d" });
+    // limit: caller value preserved
+    expect(result.limit).toBe(50);
+    // sort: default applied (raw)
+    expect(result.sort).toBe("date");
+    // fresh: default applied (raw)
+    expect(result.fresh).toBe(false);
+    // query: undefined stripped, no default → absent
+    expect("query" in result).toBe(false);
+  });
+});