diff --git a/packages/codemode/interpreter-support.md b/packages/codemode/interpreter-support.md
index e780547fcd01..072d08dd047a 100644
--- a/packages/codemode/interpreter-support.md
+++ b/packages/codemode/interpreter-support.md
@@ -114,10 +114,10 @@ ultimate source of truth.
 - [x] Equality and ordering: `==`, `!=`, `===`, `!==`, `<`, `<=`, `>`, and `>=`.
 - [x] Bitwise operators: `&`, `|`, `^`, `~`, `<<`, `>>`, and `>>>`.
 - [x] Logical operators: `&&`, `||`, `??`, and `!`, with short-circuiting.
-- [x] Unary `+`, unary `-`, `typeof`, `instanceof`, and own-property-only `in`.
+- [x] Unary `+`, unary `-`, `void`, `typeof`, `instanceof`, and own-property-only `in`.
 - [x] Prefix and postfix `++` and `--`.
 - [x] Plain, arithmetic, bitwise, and logical assignment operators.
-- [ ] Unary `void` and property deletion, including computed forms such as `delete object[key]`.
+- [ ] Property deletion, including computed forms such as `delete object[key]`.
 
 ## Promises and tools
 
@@ -172,7 +172,7 @@ ultimate source of truth.
 - [x] Prototype traversal and mutation through `__proto__`, `constructor`, and `prototype` are blocked.
 - [ ] Legal own data fields named `__proto__`, `constructor`, or `prototype` are rejected at JSON/tool boundaries and
       cannot be created, read, or written in CodeMode; tool path segments with those names remain supported.
-- [ ] `Object.is` for supported data values.
+- [x] `Object.is` for supported data values.
 - [ ] `Object.groupBy`.
 
 ## Arrays
diff --git a/packages/codemode/src/interpreter/runtime.ts b/packages/codemode/src/interpreter/runtime.ts
index b9ed33fd6192..a333744ee08f 100644
--- a/packages/codemode/src/interpreter/runtime.ts
+++ b/packages/codemode/src/interpreter/runtime.ts
@@ -1286,6 +1286,7 @@ export class Interpreter<R> {
     return Effect.map(this.evaluateExpression(argument), (value) => {
       if (operator === "typeof") return typeofValue(value)
       if (operator === "!") return !value
+      if (operator === "void") return undefined
       if (containsOpaqueReference(value)) {
         throw new InterpreterRuntimeError("Unary operators require data values in CodeMode.", node, "InvalidDataValue")
       }
diff --git a/packages/codemode/src/stdlib/object.ts b/packages/codemode/src/stdlib/object.ts
index def400344bc8..a47370e4c87b 100644
--- a/packages/codemode/src/stdlib/object.ts
+++ b/packages/codemode/src/stdlib/object.ts
@@ -1,4 +1,5 @@
 import { type AstNode, InterpreterRuntimeError } from "../interpreter/model.js"
+import { containsOpaqueReference } from "../interpreter/references.js"
 import { isBlockedMember } from "../tool-runtime.js"
 import { isCodeModeValue, CodeModeMap, CodeModePromise, CodeModeSet, CodeModeURLSearchParams } from "../values.js"
 import { boundedData, coerceToString } from "./value.js"
@@ -44,6 +45,11 @@ export const invokeObjectMethod = (name: string, args: Array<unknown>, node: Ast
       return Object.entries(requireObject()).map(([key, item]) => [key, item])
     case "hasOwn":
       return Object.hasOwn(requireObject(), String(args[1]))
+    case "is":
+      if (containsOpaqueReference(args[0]) || containsOpaqueReference(args[1])) {
+        throw new InterpreterRuntimeError("Object.is requires data values in CodeMode.", node, "InvalidDataValue")
+      }
+      return Object.is(args[0], args[1])
     case "assign": {
       const target = args[0]
       if (target === null || typeof target !== "object" || Array.isArray(target) || isCodeModeValue(target)) {
diff --git a/packages/codemode/test/parity.test.ts b/packages/codemode/test/parity.test.ts
index 132b40b12c73..b30123db170d 100644
--- a/packages/codemode/test/parity.test.ts
+++ b/packages/codemode/test/parity.test.ts
@@ -99,6 +99,19 @@ describe("H4: typeof on an undeclared identifier is 'undefined'", () => {
   })
 })
 
+describe("unary void", () => {
+  test("evaluates its operand and returns undefined", async () => {
+    expect(await value(`let count = 0; const result = void (count += 1); return [count, result === undefined]`)).toEqual([
+      1,
+      true,
+    ])
+  })
+
+  test("discards opaque values", async () => {
+    expect(await value(`return void tools === undefined`)).toBe(true)
+  })
+})
+
 describe("H1: NaN/Infinity flow as intermediates and normalize to null at the boundary", () => {
   test("guards run instead of the program crashing on a transient NaN", async () => {
     expect(await value(`return parseInt("abc") || 0`)).toBe(0)
diff --git a/packages/codemode/test/stdlib.test.ts b/packages/codemode/test/stdlib.test.ts
index ba779f33d7d0..94d8c57b079b 100644
--- a/packages/codemode/test/stdlib.test.ts
+++ b/packages/codemode/test/stdlib.test.ts
@@ -593,6 +593,24 @@ describe("Set", () => {
 })
 
 describe("stdlib integration", () => {
+  test("Object.is uses SameValue semantics", async () => {
+    expect(
+      await value(`
+        const object = {}
+        return [
+          Object.is(NaN, NaN),
+          Object.is(0, -0),
+          Object.is(object, object),
+          Object.is({}, {}),
+        ]
+      `),
+    ).toEqual([true, false, true, false])
+  })
+
+  test("Object.is rejects opaque runtime references", async () => {
+    expect((await error(`return Object.is(Math.max, Math.max)`)).kind).toBe("InvalidDataValue")
+  })
+
   test("Object values and entries accept arrays", async () => {
     expect(await value(`return [Object.values(["a", "b"]), Object.entries(["a", "b"])]`)).toEqual([
       ["a", "b"],