diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0ee2272e..78f2e793 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -300,8 +300,8 @@ jobs:
 
   # `@argos-ci/vitest` supports Vitest 4 and 5. The workspace is pinned to 5, so
   # these two jobs put 4 back and re-run the same suites against it. They upload
-  # under their own build names — a build name owns one baseline, and the two
-  # majors are separate baselines even when the pixels agree.
+  # under their own build names — a build name owns one baseline, and each
+  # Vitest version tested is a separate baseline even when the pixels agree.
   e2e-vitest-compat:
     timeout-minutes: 5
     strategy:
@@ -309,6 +309,10 @@ jobs:
       matrix:
         node-version: [lts/*]
         os: [ubuntu-latest]
+        # 4.0.0 is the oldest supported release: it predates `TestRunner` and
+        # the task `fullName`, so it runs the SDK's fallbacks. `4` is the latest
+        # 4.x.
+        vitest-version: ["4.0.0", "4"]
 
     runs-on: ${{ matrix.os }}
 
@@ -321,10 +325,13 @@ jobs:
         with:
           node-version: ${{ matrix.node-version }}
 
-      - name: Downgrade to Vitest 4
+      - name: Downgrade to Vitest ${{ matrix.vitest-version }}
         run: >-
-          pnpm --filter=@argos-ci/vitest up "vitest@^4" "@vitest/browser@^4"
-          "@vitest/browser-playwright@^4" "@vitest/pretty-format@^4"
+          pnpm --filter=@argos-ci/vitest up
+          "vitest@${{ matrix.vitest-version }}"
+          "@vitest/browser@${{ matrix.vitest-version }}"
+          "@vitest/browser-playwright@${{ matrix.vitest-version }}"
+          "@vitest/pretty-format@${{ matrix.vitest-version }}"
 
       - name: Run integration tests
         run: pnpm exec -- turbo run e2e-compat --filter=@argos-ci/vitest
@@ -332,6 +339,7 @@ jobs:
           ARGOS_TOKEN: ${{ secrets.ARGOS_TOKEN }}
           NODE_VERSION: ${{ matrix.node-version }}
           OS: ${{ matrix.os }}
+          VITEST_VERSION: ${{ matrix.vitest-version }}
 
   e2e-storybook-vitest-compat:
     timeout-minutes: 10
diff --git a/packages/vitest/package.json b/packages/vitest/package.json
index 14bce7e4..7a090a4a 100644
--- a/packages/vitest/package.json
+++ b/packages/vitest/package.json
@@ -77,7 +77,7 @@
     "install-playwright": "playwright install chromium --with-deps",
     "build-e2e": "pnpm run install-playwright",
     "e2e": "cross-env BUILD_NAME=\"argos-vitest-e2e-node-$NODE_VERSION-$OS\" UPLOAD_TO_ARGOS=true pnpm run test-e2e",
-    "e2e-compat": "cross-env BUILD_NAME=\"argos-vitest4-e2e-node-$NODE_VERSION-$OS\" UPLOAD_TO_ARGOS=true pnpm run test-e2e",
+    "e2e-compat": "cross-env BUILD_NAME=\"argos-vitest$VITEST_VERSION-e2e-node-$NODE_VERSION-$OS\" UPLOAD_TO_ARGOS=true pnpm run test-e2e",
     "check-types": "tsc",
     "check-format": "prettier --check --ignore-unknown --ignore-path=./.gitignore --ignore-path=../../.gitignore --ignore-path=../../.prettierignore .",
     "lint": "eslint ."
diff --git a/packages/vitest/src/auto-name.test.ts b/packages/vitest/src/auto-name.test.ts
index 45fb5563..e42cae6f 100644
--- a/packages/vitest/src/auto-name.test.ts
+++ b/packages/vitest/src/auto-name.test.ts
@@ -1,6 +1,13 @@
-import { expect, it } from "vitest";
+import { describe, expect, it, vi } from "vitest";
 import { TestRunner } from "vitest";
 import { resolveAutoName } from "./auto-name";
+import { getCurrentTest } from "./test-context";
+
+// The real implementation, unless a test swaps in a task of its own.
+vi.mock(import("./test-context"), async (importOriginal) => {
+  const actual = await importOriginal();
+  return { ...actual, getCurrentTest: vi.fn(actual.getCurrentTest) };
+});
 
 it("returns an explicit name verbatim", async () => {
   await expect(resolveAutoName("button")).resolves.toBe("button");
@@ -22,6 +29,20 @@ it("restarts the counter for each test", async () => {
   await expect(resolveAutoName()).resolves.toBe(`${testName} 1`);
 });
 
+describe("on Vitest < 4.0.14", () => {
+  it("rebuilds the full name, which tasks do not have yet", async () => {
+    const test = TestRunner.getCurrentTest()!;
+    vi.mocked(getCurrentTest).mockResolvedValueOnce({
+      id: test.id,
+      name: test.name,
+      file: test.file,
+      suite: test.suite,
+    });
+    // Same name as from the real `fullName`, so upgrading Vitest keeps it.
+    await expect(resolveAutoName()).resolves.toBe(`${test.fullName} 1`);
+  });
+});
+
 it("includes the test file path so names are unique across files", async () => {
   const file = TestRunner.getCurrentTest()?.file?.name;
   expect(file).toBe("src/auto-name.test.ts");
diff --git a/packages/vitest/src/auto-name.ts b/packages/vitest/src/auto-name.ts
index 2ee0c512..89ed43db 100644
--- a/packages/vitest/src/auto-name.ts
+++ b/packages/vitest/src/auto-name.ts
@@ -1,3 +1,4 @@
+import { getTitlePath } from "./metadata";
 import { getCurrentTest } from "./test-context";
 
 /**
@@ -73,11 +74,14 @@ export async function resolveAutoName(
   const count = (counters.get(test) ?? 0) + 1;
   counters.set(test, count);
 
+  // Vitest sets `fullName` from 4.0.14 on; before that, its own `getFullName()`
+  // joined the title path.
+  const testFullName = test.fullName ?? getTitlePath(test).join(" > ");
   const file = test.file?.name;
   const fullName =
-    file && !test.fullName.startsWith(file)
-      ? `${file} > ${test.fullName}`
-      : test.fullName;
+    file && !testFullName.startsWith(file)
+      ? `${file} > ${testFullName}`
+      : testFullName;
 
   // Reserve room for the trailing counter and the caller's suffix, then keep
   // the whole name within the filesystem limit. The counter always survives
diff --git a/packages/vitest/src/metadata.ts b/packages/vitest/src/metadata.ts
index 0ac838e8..66ca48c2 100644
--- a/packages/vitest/src/metadata.ts
+++ b/packages/vitest/src/metadata.ts
@@ -16,7 +16,7 @@ export type TestMetadata = ScreenshotMetadata["test"];
  * Build the title path of a task (`[file, ...describes, title]`), replicating
  * Vitest's own `getNames` helper so it matches the framework's conventions.
  */
-function getTitlePath(task: CurrentTask): string[] {
+export function getTitlePath(task: CurrentTask): string[] {
   const names = [task.name];
   let current: CurrentSuite = task;
   while (current.suite) {
diff --git a/packages/vitest/src/test-context.ts b/packages/vitest/src/test-context.ts
index ab5c7925..c811f142 100644
--- a/packages/vitest/src/test-context.ts
+++ b/packages/vitest/src/test-context.ts
@@ -14,7 +14,8 @@ export interface CurrentSuite {
 export interface CurrentTask extends CurrentSuite {
   id: string;
   name: string;
-  fullName: string;
+  /** Path of the file, describe blocks and title (Vitest >= 4.0.14). */
+  fullName?: string | undefined;
   file: { name: string; filepath: string };
   /** Tags declared on the test (Vitest >= 4). */
   tags?: string[] | undefined;
@@ -36,25 +37,38 @@ export interface CurrentTask extends CurrentSuite {
 }
 
 /**
- * Entry point exposing `getCurrentTest` before Vitest 4.1, and removed
- * altogether in Vitest 5.
+ * Global where Vitest keeps the state of the worker running the tests, in Node
+ * and in the browser alike. Vitest internal: only read on 4.0, a release line
+ * that no longer changes.
+ */
+const WORKER_STATE_GLOBAL = "__vitest_worker__";
+
+/**
+ * Get the running test from Vitest's worker state, for Vitest 4.0.
  *
- * Held in a variable rather than written inline at the import: Vite's
- * dependency pre-bundler resolves a literal specifier eagerly, and on Vitest 5
- * that fails the whole optimize step over an export that no longer exists —
- * even though the branch importing it cannot run there.
+ * Vitest 4.0 exports `getCurrentTest()` only from `vitest/suite`, which this
+ * package cannot import: written inline, the specifier fails Vite's dependency
+ * optimizer on Vitest 5, where that export is gone; hidden from Vite, it
+ * reaches the browser unresolved. The test runner also keeps the running task
+ * on the worker state, and Vitest 4.0's own browser commands
+ * (`page.screenshot()`) read it from there. The task is the test while it runs,
+ * hooks included, and its suite or file otherwise.
  */
-const LEGACY_SUITE_ENTRY = "vitest/suite";
+function getCurrentTestFromWorkerState(): CurrentTask | undefined {
+  const state = (globalThis as Record<string, unknown>)[WORKER_STATE_GLOBAL] as
+    { current?: CurrentTask & { type?: string } } | undefined;
+  const task = state?.current;
+  return task?.type === "test" ? task : undefined;
+}
 
 /**
  * Get the current Vitest test task, or `undefined` when not inside a test.
  *
  * Vitest >= 4.1 exposes `TestRunner.getCurrentTest()` from the `vitest` entry
- * point; the `vitest/suite` export is deprecated there and gone in Vitest 5. We
- * prefer the new API and fall back to `vitest/suite` for older 4.x. Both are
- * imported dynamically so importing `@argos-ci/vitest` in a non-Vitest
- * environment does not pull Vitest in — only call this once you know Vitest is
- * available.
+ * point; on Vitest 4.0, we read the worker state instead (see
+ * {@link getCurrentTestFromWorkerState}). `vitest` is imported dynamically so
+ * importing `@argos-ci/vitest` in a non-Vitest environment does not pull Vitest
+ * in — only call this once you know Vitest is available.
  */
 export async function getCurrentTest(): Promise<CurrentTask | undefined> {
   const vitest = (await import("vitest")) as {
@@ -64,8 +78,5 @@ export async function getCurrentTest(): Promise<CurrentTask | undefined> {
   if (runner?.getCurrentTest) {
     return runner.getCurrentTest();
   }
-  const suite = (await import(/* @vite-ignore */ LEGACY_SUITE_ENTRY)) as {
-    getCurrentTest: () => CurrentTask | undefined;
-  };
-  return suite.getCurrentTest();
+  return getCurrentTestFromWorkerState();
 }
diff --git a/turbo.json b/turbo.json
index 516a7697..ff3daa87 100644
--- a/turbo.json
+++ b/turbo.json
@@ -71,6 +71,7 @@
         "ARGOS_BUILD_NUMBER",
         "NODE_VERSION",
         "OS",
+        "VITEST_VERSION",
         "GITHUB_*"
       ],
       "dependsOn": ["build-e2e"],