diff --git a/.changeset/historical-snapshot-compatibility.md b/.changeset/historical-snapshot-compatibility.md
new file mode 100644
index 0000000..81de8e4
--- /dev/null
+++ b/.changeset/historical-snapshot-compatibility.md
@@ -0,0 +1,5 @@
+---
+"webgpu-search": patch
+---
+
+Add a frozen snapshot from the published 1.0.1 package to verify backward-compatible restoration, document contents, and ordered search scores in CI.
diff --git a/docs/IMPROVEMENT-PLAN.md b/docs/IMPROVEMENT-PLAN.md
index 4ccbe2c..201483c 100644
--- a/docs/IMPROVEMENT-PLAN.md
+++ b/docs/IMPROVEMENT-PLAN.md
@@ -31,6 +31,7 @@ There are about 300 tests, but several core modules have none of their own. This
 - **Why:** AGENTS.md §2.4 requires the two paths to score the same, and nothing enforces it today.
 
 ### 2.2 Snapshot codec tests
+- **Historical compatibility covered:** `scripts/test-snapshot.ts` loads the frozen `test/fixtures/snapshot-1.0.1.bin` written by the published npm package, with provenance and fixed search expectations in its JSON manifest. Existing round-trip and typed corruption/profile error checks remain in the same suite, which CI runs through `test:snapshot`.
 - Add `test/snapshot-codec.test.ts`:
   - Saving an index and loading it back gives identical search results.
   - Bad input is rejected with the right typed error: wrong magic bytes, wrong version, truncated data, a corrupted checksum, a mismatched text profile.
diff --git a/packages/webgpu-search/test/fixtures/README.md b/packages/webgpu-search/test/fixtures/README.md
new file mode 100644
index 0000000..5e83efc
--- /dev/null
+++ b/packages/webgpu-search/test/fixtures/README.md
@@ -0,0 +1,34 @@
+# Historical snapshots
+
+`snapshot-1.0.1.bin` was written by the **published npm package
+`webgpu-search@1.0.1`**, not by the working tree. Its JSON manifest records
+the npm tarball URL and integrity, input documents, index options, snapshot
+format and SHA-256, and ordered search results from that released package.
+
+The fixture protects compatibility with an older writer independently of
+current serialization code. The snapshot suite loads the bytes directly and
+checks result IDs, scores, matched fields, and restored documents. CI already
+runs it through `bun run test:snapshot`.
+
+## Preserve the fixture
+
+Do not regenerate or update this pair to make a failing test pass. Investigate
+the compatibility regression instead. Add a separately versioned fixture when
+covering another release; retain the existing ones.
+
+To reproduce the original generation in a temporary directory:
+
+1. Install `webgpu-search@1.0.1` with
+   `npm install --ignore-scripts --no-audit --no-fund --save-exact webgpu-search@1.0.1`.
+2. Verify its `package-lock.json` integrity matches `producer.integrity` in
+   the manifest. Import `DocumentIndex` from that installation, outside this
+   monorepo so workspace aliases cannot select current code.
+3. Pass the manifest's `documents` and `options` to `DocumentIndex.create()`.
+   Write `new Uint8Array(index.serialize())` to a temporary file.
+4. Run each manifest query using its `mode` and `cpuScorer: 'exact'`. Compare
+   `totalMatches` and ordered `{ id, score, matchedField }` against `expected`.
+   Destroy the index when finished.
+
+The resulting file must match `snapshotSha256`; reproduction must not overwrite
+the checked-in artifact. Queries cover weighted multi-field ranking, ASCII,
+German and Greek case folding, decomposed accents, CJK, emoji/ZWJ, and no hits.
diff --git a/packages/webgpu-search/test/fixtures/snapshot-1.0.1.bin b/packages/webgpu-search/test/fixtures/snapshot-1.0.1.bin
new file mode 100644
index 0000000..4598e89
Binary files /dev/null and b/packages/webgpu-search/test/fixtures/snapshot-1.0.1.bin differ
diff --git a/packages/webgpu-search/test/fixtures/snapshot-1.0.1.json b/packages/webgpu-search/test/fixtures/snapshot-1.0.1.json
new file mode 100644
index 0000000..e7ba4ac
--- /dev/null
+++ b/packages/webgpu-search/test/fixtures/snapshot-1.0.1.json
@@ -0,0 +1,187 @@
+{
+  "producer": {
+    "package": "webgpu-search",
+    "version": "1.0.1",
+    "tarball": "https://registry.npmjs.org/webgpu-search/-/webgpu-search-1.0.1.tgz",
+    "integrity": "sha512-psu6FVagazLpKH1miZez3PqIYhZ2rqBLDupogh7D5nZIr6teC6RpvgYEtm0v3m3MEuV2ll/JTdzz0JVwAPmApQ=="
+  },
+  "options": {
+    "fields": [
+      {
+        "name": "title",
+        "weight": 2
+      },
+      {
+        "name": "content",
+        "weight": 1
+      }
+    ],
+    "preferGpu": false
+  },
+  "documents": [
+    {
+      "id": "ascii-1",
+      "title": "WebGPU search",
+      "content": "Fast parallel search for documents."
+    },
+    {
+      "id": "ascii-2",
+      "title": "Search guide",
+      "content": "WebGPU search with a CPU fallback."
+    },
+    {
+      "id": "unicode",
+      "title": "Straße café",
+      "content": "İstanbul and Greek Σ σ ς."
+    },
+    {
+      "id": "cjk",
+      "title": "東京 検索",
+      "content": "日本語 search guide."
+    },
+    {
+      "id": "emoji",
+      "title": "Developer 👩‍💻",
+      "content": "Launch 🚀 with emoji."
+    }
+  ],
+  "queries": [
+    {
+      "query": "webgpu",
+      "mode": "substring",
+      "expected": {
+        "totalMatches": 2,
+        "results": [
+          {
+            "id": "ascii-1",
+            "score": 1986,
+            "matchedField": "title"
+          },
+          {
+            "id": "ascii-2",
+            "score": 972,
+            "matchedField": "content"
+          }
+        ]
+      }
+    },
+    {
+      "query": "search",
+      "mode": "fuzzy",
+      "expected": {
+        "totalMatches": 3,
+        "results": [
+          {
+            "id": "ascii-2",
+            "score": 748,
+            "matchedField": "title"
+          },
+          {
+            "id": "ascii-1",
+            "score": 726,
+            "matchedField": "title"
+          },
+          {
+            "id": "cjk",
+            "score": 359,
+            "matchedField": "content"
+          }
+        ]
+      }
+    },
+    {
+      "query": "strasse",
+      "mode": "substring",
+      "expected": {
+        "totalMatches": 1,
+        "results": [
+          {
+            "id": "unicode",
+            "score": 1990,
+            "matchedField": "title"
+          }
+        ]
+      }
+    },
+    {
+      "query": "café",
+      "mode": "substring",
+      "expected": {
+        "totalMatches": 1,
+        "results": [
+          {
+            "id": "unicode",
+            "score": 1824,
+            "matchedField": "title"
+          }
+        ]
+      }
+    },
+    {
+      "query": "σ",
+      "mode": "substring",
+      "expected": {
+        "totalMatches": 1,
+        "results": [
+          {
+            "id": "unicode",
+            "score": 775,
+            "matchedField": "content"
+          }
+        ]
+      }
+    },
+    {
+      "query": "東京",
+      "mode": "substring",
+      "expected": {
+        "totalMatches": 1,
+        "results": [
+          {
+            "id": "cjk",
+            "score": 1994,
+            "matchedField": "title"
+          }
+        ]
+      }
+    },
+    {
+      "query": "👩‍💻",
+      "mode": "substring",
+      "expected": {
+        "totalMatches": 1,
+        "results": [
+          {
+            "id": "emoji",
+            "score": 1780,
+            "matchedField": "title"
+          }
+        ]
+      }
+    },
+    {
+      "query": "🚀",
+      "mode": "substring",
+      "expected": {
+        "totalMatches": 1,
+        "results": [
+          {
+            "id": "emoji",
+            "score": 911,
+            "matchedField": "content"
+          }
+        ]
+      }
+    },
+    {
+      "query": "absent-query",
+      "mode": "substring",
+      "expected": {
+        "totalMatches": 0,
+        "results": []
+      }
+    }
+  ],
+  "snapshotSha256": "b34c39e7698e5b1d0054b57b6f4d07b5ca1a41661787cf8267ea1f9241297ff2",
+  "snapshotFormatVersion": 4
+}
diff --git a/scripts/test-snapshot.ts b/scripts/test-snapshot.ts
index 993a905..baa17ba 100644
--- a/scripts/test-snapshot.ts
+++ b/scripts/test-snapshot.ts
@@ -1,4 +1,7 @@
 import assert from 'node:assert';
+import { createHash } from 'node:crypto';
+import { readFile } from 'node:fs/promises';
+import snapshotFixture from '../packages/webgpu-search/test/fixtures/snapshot-1.0.1.json';
 import {
   DocumentIndex,
   SearchWorkerClient,
@@ -1571,6 +1574,38 @@ async function runSnapshotTests() {
     console.log('   ✅ Profile guards + live-format semantics confirmed');
   }
 
+  // Unlike live round-trips, these bytes and expectations come from the
+  // published 1.0.1 writer and must survive changes to the current encoder.
+  console.log('18. Testing the frozen webgpu-search@1.0.1 snapshot...');
+  {
+    const bytes = await readFile(new URL(
+      '../packages/webgpu-search/test/fixtures/snapshot-1.0.1.bin', import.meta.url
+    ));
+    assert.strictEqual(createHash('sha256').update(bytes).digest('hex'), snapshotFixture.snapshotSha256);
+    const snapshot = Uint8Array.from(bytes).buffer;
+    assert.strictEqual(decodeSnapshotHeader(snapshot).formatVersion, snapshotFixture.snapshotFormatVersion);
+    const restored = await DocumentIndex.fromSnapshot(snapshot, { options: { preferGpu: false } });
+    try {
+      assert.strictEqual(restored.getStats().docCount, snapshotFixture.documents.length);
+      for (const entry of snapshotFixture.queries) {
+        const response = await restored.search(entry.query, {
+          mode: entry.mode as 'fuzzy' | 'substring',
+          cpuScorer: 'exact',
+        });
+        assert.deepStrictEqual({
+          totalMatches: response.totalMatches,
+          results: response.results.map(({ id, score, matchedField }) => ({ id, score, matchedField })),
+        }, entry.expected, `1.0.1 snapshot search changed for ${JSON.stringify(entry.query)}`);
+        for (const hit of response.results) {
+          assert.deepStrictEqual(hit.doc, snapshotFixture.documents.find(doc => doc.id === hit.id));
+        }
+      }
+    } finally {
+      restored.destroy();
+    }
+    console.log('   ✅ Published 1.0.1 snapshot compatibility confirmed');
+  }
+
   console.log('\n--- All Persistence Tests Passed Successfully! ✅ ---');
 }