diff --git a/packages/vitest/src/node/config/resolveConfig.ts b/packages/vitest/src/node/config/resolveConfig.ts
index 8e826edd8..1b9703369 100644
--- a/packages/vitest/src/node/config/resolveConfig.ts
+++ b/packages/vitest/src/node/config/resolveConfig.ts
@@ -557,6 +557,15 @@ export function resolveTestConfig(
   resolved.deps.moduleDirectories ??= []
 
   resolved.deps.optimizer ??= {}
+  // `deps.optimizer` is keyed by Vite environment name, so `web` is a valid
+  // key when the user declares that environment themselves
+  // (`vite.environments.web`) - only the Vitest 3 alias for `client` is
+  // silently ignored
+  if (resolved.deps.optimizer.web && !viteConfig.environments.web) {
+    logger.deprecate(
+      '`deps.optimizer.web` is deprecated. Use `deps.optimizer.client` instead (or `deps.optimizer.ssr` for `node` and `edge` environments).',
+    )
+  }
   resolved.deps.optimizer.ssr ??= {}
   resolved.deps.optimizer.ssr.enabled ??= false
   resolved.deps.optimizer.client ??= {}
diff --git a/test/e2e/test/cache.test.ts b/test/e2e/test/cache.test.ts
index 61e9ac60d..baddb61ef 100644
--- a/test/e2e/test/cache.test.ts
+++ b/test/e2e/test/cache.test.ts
@@ -89,7 +89,7 @@ test('preserves previous test results', async () => {
 describe('with optimizer enabled', () => {
   const deps = {
     optimizer: {
-      web: {
+      client: {
         enabled: true,
       },
     },
diff --git a/test/e2e/test/config/deps-optimizer.test.ts b/test/e2e/test/config/deps-optimizer.test.ts
new file mode 100644
index 000000000..8d4085801
--- /dev/null
+++ b/test/e2e/test/config/deps-optimizer.test.ts
@@ -0,0 +1,57 @@
+import { expect, test } from 'vitest'
+import { resolveTestConfig, runInlineTests } from '../../../test-utils'
+
+test('deps.optimizer.web is deprecated in favour of deps.optimizer.client', async () => {
+  const { stderr } = await runInlineTests(
+    { 'basic.test.ts': 'test("passes", () => {})' },
+    {
+      deps: {
+        optimizer: {
+          web: { enabled: true },
+        },
+      },
+    },
+  )
+  expect(stderr).toContain('`deps.optimizer.web` is deprecated')
+  expect(stderr).toContain('Use `deps.optimizer.client` instead')
+})
+
+test('deps.optimizer.client is not deprecated', async () => {
+  const { stderr } = await runInlineTests(
+    { 'basic.test.ts': 'test("passes", () => {})' },
+    {
+      deps: {
+        optimizer: {
+          client: { enabled: false },
+        },
+      },
+    },
+  )
+  expect(stderr).not.toContain('`deps.optimizer.web` is deprecated')
+})
+
+test('deps.optimizer.web is deprecated only without a `web` environment', async () => {
+  // `deps.optimizer` is keyed by Vite environment name, so `web` is a valid key
+  // when the user declares that environment themselves - only the Vitest 3
+  // alias for `client` is silently ignored
+  const web = { enabled: true }
+
+  const withoutEnvironment = await resolveTestConfig({
+    deps: {
+      optimizer: { web },
+    },
+  })
+  expect(withoutEnvironment.stderr).toContain('`deps.optimizer.web` is deprecated')
+
+  const withEnvironment = await resolveTestConfig({
+    deps: {
+      optimizer: { web },
+    },
+    $viteConfig: {
+      environments: {
+        web: {},
+      },
+    },
+  })
+  expect(withEnvironment.stderr).not.toContain('`deps.optimizer.web` is deprecated')
+})