# Chrome OnDeviceHeadSuggest - Complete Technical Analysis

## Overview

**OnDeviceHeadSuggest** is Chrome's offline autocomplete system. It provides search query suggestions in the omnibox without any network connection, using a compressed radix tree (trie) stored locally as a binary file.

- **Component ID**: `obedbbhbpmojnkanicioggnmelmoomoc`
- **Previous Component ID** (before July 2019): `feejiaigafnbpeeogmhmjfmkcjplcneb`
- **Source**: `components/component_updater/installer_policies/on_device_head_suggest_component_installer.cc`
- **Model reader**: `components/omnibox/browser/on_device_head_model.h`
- **Provider**: `components/omnibox/browser/on_device_head_provider.cc`

---

## Architecture

### Single Component, Multiple Locales

There is **one single component ID** for all locales. The locale is communicated via an `accept_locale` installer attribute in the update request. Google's server returns the locale-specific CRX file.

```
Component ID: obedbbhbpmojnkanicioggnmelmoomoc
   ├── accept_locale=FR          → cr_fr_100000_index.bin       (100K, ~1.2 MB)
   ├── accept_locale=FR500000    → cr_fr_500000_index.bin       (500K, ~7.4 MB)
   ├── accept_locale=ENUS        → cr_en-us_100000_index.bin    (100K, ~1.3 MB)
   ├── accept_locale=ENUS500000  → cr_en-us_500000_index.bin    (500K, ~7.7 MB)
   ├── accept_locale=DE          → cr_de_100000_index.bin       (100K, ~1.3 MB)
   ├── accept_locale=DE500000    → cr_de_500000_index.bin       (500K, ~7.6 MB)
   └── ... (19 languages × 2 tiers + country variants)
```

### Locale Normalization

Chrome normalizes the browser locale before requesting:
- Removes hyphens and underscores
- Converts to uppercase
- Appends model size constraint (default: `500000`)

| Browser Locale | Normalized | Manifest Name |
|---|---|---|
| `fr` | `FR` | `OnDeviceHeadSuggestFR500000` |
| `en-US` | `ENUS` | `OnDeviceHeadSuggestENUS500000` |
| `pt-BR` | `PTBR` | `OnDeviceHeadSuggestPTBR500000` |
| `zh-TW` | `ZHTW` | `OnDeviceHeadSuggestZHTW500000` |

### Locale Exclusions

Korean (`ko`, `ko-KR`) is **explicitly disabled** in Chromium source:

```cpp
bool OmniboxFieldTrial::IsOnDeviceHeadSuggestEnabledForLocale(
    const std::string& locale) {
  if (IsKoreanLocale(locale)) return false;
  return IsOnDeviceHeadSuggestEnabledForAnyMode();
}
```

### Chrome Stable vs Canary

The OnDeviceHeadSuggest model is **identical bit-for-bit** between Chrome Stable and Chrome Canary. Verified on 2026-03-15:

| | Chrome Canary | Chrome Stable |
|---|---|---|
| **Path** | `AppData/Local/Google/Chrome SxS/User Data/components/OnDeviceHeadSuggestModel/` | `AppData/Local/Google/Chrome/User Data/OnDeviceHeadSuggestModel/` |
| **Version** | `20251024.824731831.14` | `20251024.824731831.14` |
| **File** | `cr_fr_500000_index.bin` (7,578,989 bytes) | `cr_fr_500000_index.bin` (7,578,989 bytes) |
| **MD5** | `3203842440b708ef7a3ccc70425d2681` | `3203842440b708ef7a3ccc70425d2681` |

**Note**: In Chrome Stable, the component lives directly under `User Data/OnDeviceHeadSuggestModel/`, not under `User Data/components/` as might be expected. The same model version and binary are served to both channels.

### Model Tiers: 100K vs 500K

Each locale is available in **two tiers**:

| Tier | accept_locale example | Manifest name | Suggestions | Typical size |
|---|---|---|---|---|
| **100K** (default) | `FR`, `ENUS`, `DE` | `OnDeviceHeadSuggestFR` | ~100,000 | 0.7 - 3.2 MB |
| **500K** (full) | `FR500000`, `ENUS500000`, `DE500000` | `OnDeviceHeadSuggestFR500000` | 500,000 | 4.2 - 15.3 MB |

- The **100K tier** is what Chrome downloads by default (smaller, faster)
- The **500K tier** is the full model installed locally by Chrome (the one found in `User Data/OnDeviceHeadSuggestModel/`)
- The volume suffix (`500000`) is appended by the client based on locale configuration. The server decides which tier to serve based on the `accept_locale` value
- File naming: `cr_{locale}_{volume}_index.bin` (e.g., `cr_fr-fr_100000_index.bin` for 100K, `cr_fr_500000_index.bin` for 500K)

---

## Binary Format Specification

Source: `components/omnibox/browser/on_device_head_model.h`

### File Header (2 bytes)

```
Offset 0: [address_size: 1 byte] - Size of address pointers in bytes
Offset 1: [score_size: 1 byte]   - Size of score values in bytes
Offset 2: [root_node]            - Root of the radix tree starts here
```

For the FR 500K model: `address_size = 4`, `score_size = 3`

### Node Structure

Each node in the radix tree:

```
[max_score_as_root block]
[child_0] [child_1] ... [child_N]
[0x00 terminator]
```

### max_score_as_root Block

```
┌─────────────────────────────────────────────┐
│ score_size bytes, little-endian             │
│   bit 0:    has_leaf_score flag             │
│   bits 1+:  maximum score in this subtree   │
├─────────────────────────────────────────────┤
│ if has_leaf_score:                          │
│   score_size more bytes = leaf_score        │
│   (this prefix IS a complete suggestion)    │
└─────────────────────────────────────────────┘
```

- **score_max** (bits 1+): Used for **pruning** - Chrome skips entire subtrees where score_max < threshold
- **leaf_score**: The actual popularity score if this exact prefix is a suggestion
- **has_leaf_score** (bit 0): Indicates whether this node represents a complete query

### Child Structure

```
┌───────────────────────────────────────┐
│ [text_length: 1 byte]                │
│ [text: text_length bytes, UTF-8]     │
│ [indicator block]                     │
└───────────────────────────────────────┘
```

**Indicator block** (first byte determines type):

```
bit 0 = 0 → LEAF child
  Remaining: score_size - 1 bytes
  Full block value >> 1 = leaf_score

bit 0 = 1 → INTERMEDIATE child
  Remaining: address_size - 1 bytes
  Full block value >> 1 = address (offset in file to child node)
```

### Visual Example

```
File offset 2 (root):
  [max_score_as_root: 0xFF FF FE]  → has_leaf=0, score_max=8388607

  Child "d":
    text_length=1, text="d"
    first_byte=0x05, remaining=[0x00, 0x00]
    is_leaf=0 (bit0=1→intermediate), address=0x000002 >> 1 = ...
    → points to subtree for prefix "d"

  Child "decathlon":
    text_length=9, text="decathlon"
    first_byte=0xFE, remaining=[0xFF, 0x3F]
    is_leaf=1 (bit0=0→leaf), score = 0x3FFFFE >> 1 = 8388607
    → "decathlon" with score 8,388,607 (maximum)

  [0x00] terminator
```

---

## Score System

### Score Parameters (FR 500K)

| Parameter | Value |
|---|---|
| Score size | 3 bytes (24 bits) |
| Usable bits | 23 (1 bit reserved for has_leaf flag) |
| Max possible score | 8,388,607 (2^23 - 1) |
| Score range (observed) | 1 - 8,388,607 |

### What the Score Represents

The score is a **quantized popularity index** derived from Google Search query frequency data:

- **Higher score** = more popular search query
- **Score 8,388,607** (max) = most popular query for that locale
- Values are **relative within the locale** - not comparable across locales
- Not raw search volume counts, but a normalized ranking metric

### Score_Max_Subtree (Pruning)

Each intermediate node stores the **maximum score** among all descendants:

```
"dec" (score_max = 8,388,607)
  ├── "athlon"     → leaf_score 8,388,607  ← (this is the max)
  ├── "oration"    → leaf_score 3,200,000
  ├── "embre"      → leaf_score 2,800,000
  └── "laration"   → leaf_score 1,500,000
```

**Purpose**: When Chrome traverses the tree looking for suggestions:
1. If a subtree's `score_max` < minimum display threshold → **skip entire branch**
2. This reduces search from O(500K) to exploring only high-scoring branches
3. Critical for real-time autocomplete performance (< 10ms response)

### How Chrome Uses Scores

From `on_device_head_provider.cc`:

1. User types a prefix in the omnibox
2. Chrome walks the radix tree to find the matching node
3. Collects top-N suggestions from that subtree (pruning low score_max branches)
4. Ranks suggestions by leaf_score descending
5. Returns top matches (typically 3-5 suggestions)

---

## Model Statistics (FR 500K)

| Metric | Value |
|---|---|
| File | `cr_fr_500000_index.bin` |
| Size | 7.23 MB |
| Address size | 4 bytes (31-bit addresses) |
| Score size | 3 bytes (23-bit scores) |
| Total suggestions | 500,000 |
| Extraction time | ~0.7 seconds |
| Shannon entropy | 6.66 bits/byte |
| Primary script | Latin (~99%) |

### Top 20 Suggestions (FR)

| Rank | Score | Suggestion |
|---|---|---|
| 1 | 8,388,607 | decathlon |
| 2 | 8,388,606 | leboncoin |
| 3 | 8,388,605 | youtube |
| 4 | 8,388,604 | amazon |
| 5 | 8,388,603 | google maps |
| 6 | 8,388,602 | traducteur |
| 7 | 8,388,601 | meteo |
| 8 | 8,388,600 | netflix |
| 9 | 8,388,599 | chatgpt |
| 10 | 8,388,598 | facebook |

*(Full list of 500,000 entries exported to `chrome_headsuggest_fr_500k.xlsx`)*

---

## Component Update Protocol

### Endpoint

```
POST https://update.googleapis.com/service/update2/json
```

### Request Format (Omaha Protocol 3.1)

**Minimal working request** (verified 2026-03-15):

```json
{
  "request": {
    "protocol": "3.1",
    "dedup": "cr",
    "acceptformat": "crx3",
    "prodversion": "131.0.6778.86",
    "sessionid": "{UUID}",
    "requestid": "{UUID}",
    "@os": "win",
    "arch": "x64",
    "nacl_arch": "x86-64",
    "os": {"platform": "Windows", "version": "10.0.19045", "arch": "x86_64"},
    "updater": {
      "name": "Chrome",
      "version": "131.0.6778.86",
      "prodversion": "131.0.6778.86",
      "ismachine": false,
      "autoupdatecheckenabled": true,
      "updatepolicy": -1
    },
    "hw": {"physmemory": 16},
    "app": [{
      "appid": "obedbbhbpmojnkanicioggnmelmoomoc",
      "version": "0.0.0.0",
      "installedby": "policy",
      "accept_locale": "FR500000",
      "enabled": true,
      "updatecheck": {},
      "ping": {"r": -1}
    }]
  }
}
```

### Key Fields

| Field | Description |
|---|---|
| `appid` | Always `obedbbhbpmojnkanicioggnmelmoomoc` |
| `accept_locale` | Normalized locale + optional volume (e.g., `FR`, `ENUS`, `FR500000`, `ENUS500000`) |
| `version` | Set to `"0.0.0.0"` to force download, or current version to check for updates |
| `installedby` | **CRITICAL**: Must be `"policy"` for the server to respond with download URLs |
| `prodversion` | Chrome version string (e.g., `"131.0.6778.86"`) - **required** |
| `updater.name` | Must be `"Chrome"` (not `"Chromium"`) |
| `acceptformat` | `crx3` (signed Chrome extension format) |

> **Important discovery**: Without `"installedby": "policy"` and `"prodversion"` in the request, the server always returns `"noupdate"` regardless of locale. These two fields are essential for the API to return actual download URLs.

### Response

The server returns a JSON response with:
- `status`: `"ok"` (update available) or `"noupdate"`
- `urls.url.codebase`: Base URL for CRX download
- `manifest.version`: Version string (e.g., `20251024.824731831.14`)
- `manifest.packages.package`: Filename, hash, size

### Download URLs

CRX files are served from Google CDN:

```
https://edgedl.me.gvt1.com/edgedl/release2/chrome_component/{hash}_{version}/{filename}.crx3
```

### CRX3 Structure

The downloaded `.crx3` file is a signed Chrome extension containing:
- `manifest.json` with name and version
- `_metadata/verified_contents.json` (integrity hashes)
- `cr_{locale}_{count}_index.bin` (the actual model file)

---

## Available Locales (verified 2026-03-15)

### 100K Tier (default/lightweight)

**39 locale models downloaded** (56.01 MB total). Contains ~100,000 suggestions each. Most at version `20251024.824731831.14`, two at newer `20251029.826691377.14`.

| Locale | Language | Version | CRX Size |
|---|---|---|---|
| `EN` | English (generic) | 20251024.824731831.14 | 1.24 MB |
| `ENUS` | English (US) | 20251024.824731831.14 | 1.29 MB |
| `ENGB` | English (GB) | 20251024.824731831.14 | 1.29 MB |
| `ENAU` | English (AU) | 20251024.824731831.14 | 1.30 MB |
| `ENIN` | English (India) | 20251024.824731831.14 | 1.35 MB |
| `ENZA` | English (South Africa) | 20251024.824731831.14 | 1.42 MB |
| `FR` | French | 20251024.824731831.14 | 1.21 MB |
| `FRFR` | French (France) | 20251024.824731831.14 | 1.24 MB |
| `DE` | German | 20251024.824731831.14 | 1.28 MB |
| `DEDE` | German (Germany) | 20251024.824731831.14 | 1.30 MB |
| `ES` | Spanish | 20251024.824731831.14 | 1.27 MB |
| `ESES` | Spanish (Spain) | 20251024.824731831.14 | 1.30 MB |
| `ESMX` | Spanish (Mexico) | 20251024.824731831.14 | 1.36 MB |
| `IT` | Italian | 20251024.824731831.14 | 1.33 MB |
| `ITIT` | Italian (Italy) | 20251024.824731831.14 | 1.34 MB |
| `PTBR` | Portuguese (Brazil) | 20251024.824731831.14 | 1.30 MB |
| `JA` | Japanese | 20251024.824731831.14 | 1.40 MB |
| `JAJP` | Japanese (Japan) | 20251024.824731831.14 | 1.40 MB |
| `RU` | Russian | 20251024.824731831.14 | 1.86 MB |
| `RURU` | Russian (Russia) | 20251024.824731831.14 | 1.94 MB |
| `AR` | Arabic | 20251024.824731831.14 | 1.83 MB |
| `ARAE` | Arabic (UAE) | 20251024.824731831.14 | 1.81 MB |
| `AREG` | Arabic (Egypt) | 20251024.824731831.14 | 1.90 MB |
| `HI` | Hindi | 20251024.824731831.14 | 1.74 MB |
| `HIIN` | Hindi (India) | 20251024.824731831.14 | 1.74 MB |
| `TH` | Thai | 20251024.824731831.14 | 1.15 MB |
| `THTH` | Thai (Thailand) | 20251024.824731831.14 | 1.15 MB |
| `VI` | Vietnamese | 20251024.824731831.14 | 0.75 MB |
| `VIVN` | Vietnamese (Vietnam) | 20251024.824731831.14 | 0.74 MB |
| `ID` | Indonesian | 20251024.824731831.14 | 0.69 MB |
| `IDID` | Indonesian (ID) | 20251024.824731831.14 | 0.66 MB |
| `PL` | Polish | 20251024.824731831.14 | 1.33 MB |
| `PLPL` | Polish (Poland) | **20251029.826691377.14** | 1.33 MB |
| `TR` | Turkish | 20251024.824731831.14 | 1.47 MB |
| `TRTR` | Turkish (Turkey) | 20251024.824731831.14 | 1.48 MB |
| `RO` | Romanian | 20251024.824731831.14 | 1.31 MB |
| `RORO` | Romanian (Romania) | **20251029.826691377.14** | 1.32 MB |
| `BN` | Bengali | 20251024.824731831.14 | 3.00 MB |
| `BNBD` | Bengali (Bangladesh) | 20251024.824731831.14 | 3.18 MB |

### 500K Tier (full model)

**19 locale models available** (~160 MB total estimated). Contains 500,000 suggestions each. These are the full models that Chrome installs locally. Discovered 2026-03-15.

| accept_locale | Language | CRX Size | .bin Size (approx) |
|---|---|---|---|
| `ENUS500000` | English (US) | 7.75 MB | 7.93 MB |
| `ENGB500000` | English (GB) | 7.74 MB | ~7.9 MB |
| `FR500000` | French | 7.41 MB | 7.58 MB |
| `DE500000` | German | 7.61 MB | ~7.8 MB |
| `ES500000` | Spanish | 7.77 MB | ~7.9 MB |
| `ESMX500000` | Spanish (Mexico) | 8.24 MB | ~8.4 MB |
| `IT500000` | Italian | 8.00 MB | ~8.2 MB |
| `PTBR500000` | Portuguese (Brazil) | 7.91 MB | ~8.1 MB |
| `RU500000` | Russian | **10.97 MB** | ~11.2 MB |
| `JA500000` | Japanese | 7.90 MB | ~8.1 MB |
| `AR500000` | Arabic | **10.61 MB** | ~10.8 MB |
| `HI500000` | Hindi | 9.17 MB | ~9.4 MB |
| `TH500000` | Thai | 6.49 MB | ~6.6 MB |
| `VI500000` | Vietnamese | 4.60 MB | ~4.7 MB |
| `PL500000` | Polish | 7.97 MB | ~8.1 MB |
| `TR500000` | Turkish | 8.66 MB | ~8.8 MB |
| `ID500000` | Indonesian | 4.23 MB | ~4.3 MB |
| `RO500000` | Romanian | 7.82 MB | ~8.0 MB |
| `BN500000` | Bengali | **15.27 MB** | ~15.6 MB |

> **Note**: The 500K tier is available for **both** base locale codes (`FR500000`) and country-specific variants (`FRFR500000`, `DEDE500000`, etc.). All 23 country-specific 500K variants tested were available. Only `AR500000` had a different version (`20251029.826691377.14`); all others match `20251024.824731831.14`.

### 500K Tier - Country-Specific Variants (verified 2026-03-15)

| accept_locale | Language | CRX Size |
|---|---|---|
| `ENUS500000` | English (US) | 7.57 MB |
| `ENGB500000` | English (GB) | 7.56 MB |
| `ENAU500000` | English (AU) | 7.56 MB |
| `ENIN500000` | English (India) | 7.90 MB |
| `ENZA500000` | English (South Africa) | 8.25 MB |
| `FRFR500000` | French (France) | 7.31 MB |
| `DEDE500000` | German (Germany) | 7.51 MB |
| `ESES500000` | Spanish (Spain) | 7.67 MB |
| `ESMX500000` | Spanish (Mexico) | 8.05 MB |
| `ITIT500000` | Italian (Italy) | 7.84 MB |
| `PTBR500000` | Portuguese (Brazil) | 7.72 MB |
| `JAJP500000` | Japanese (Japan) | 7.71 MB |
| `RURU500000` | Russian (Russia) | **11.20 MB** |
| `ARAE500000` | Arabic (UAE) | 10.19 MB |
| `AREG500000` | Arabic (Egypt) | **10.74 MB** |
| `HIIN500000` | Hindi (India) | 8.95 MB |
| `THTH500000` | Thai (Thailand) | 6.34 MB |
| `VIVN500000` | Vietnamese (Vietnam) | 4.44 MB |
| `IDID500000` | Indonesian (ID) | 3.98 MB |
| `PLPL500000` | Polish (Poland) | 7.81 MB |
| `TRTR500000` | Turkish (Turkey) | 8.50 MB |
| `RORO500000` | Romanian (Romania) | 7.68 MB |
| `BNBD500000` | Bengali (Bangladesh) | **16.09 MB** |

### Not Available (79 locales tested, no model)

`ENCA`, `ENNZ`, `ENSG`, `ENHK`, `ENPH`, `FRBE`, `FRCH`, `FRCA`, `DEAT`, `DECH`, `ES419`, `ESAR`, `ESCO`, `ESCL`, `ESPE`, `PTPT`, `PT`, `ARSA`, `BNIN`, `NL`, `NLNL`, `NLBE`, `SV`, `SVSE`, `DA`, `DADK`, `FI`, `FIFI`, `NO`, `NBNO`, `NB`, `CS`, `CSCZ`, `UK`, `UKUA`, `HU`, `HUHU`, `EL`, `ELGR`, `BG`, `BGBG`, `HR`, `HRHR`, `SK`, `SKSK`, `SL`, `SLSI`, `HE`, `HEIL`, `ZH`, `ZHCN`, `ZHTW`, `ZHHK`, `KO` (blocked in source), `KOKR` (blocked in source), `FA`, `FAIR`, `MS`, `MSMY`, `TA`, `TAIN`, `TE`, `TEIN`, `KN`, `KNIN`, `ML`, `MLIN`, `MR`, `MRIN`, `GU`, `GUIN`, `PA`, `PAIN`, `SW`, `SWKE`, `FIL`, `FILPH`, `UR`, `URPK`

### Version Notes

- Most locales: `20251024.824731831.14` (October 24, 2025)
- `PLPL` and `RORO`: `20251029.826691377.14` (October 29, 2025 - 5 days newer)
- `AR500000`: `20251029.826691377.14` (October 29, 2025)
- No Chinese, Korean, Dutch, Scandinavian, or Eastern European models available

---

## Chromium Source References

| File | Purpose |
|---|---|
| `components/component_updater/installer_policies/on_device_head_suggest_component_installer.cc` | Component registration, locale handling, CRX verification |
| `components/component_updater/installer_policies/on_device_head_suggest_component_installer.h` | Header with public API |
| `components/omnibox/browser/on_device_head_model.h` | Binary format spec, tree reader |
| `components/omnibox/browser/on_device_head_model.cc` | Tree traversal implementation |
| `components/omnibox/browser/on_device_head_provider.cc` | Omnibox integration, suggestion provider |
| `components/omnibox/browser/on_device_model_update_listener.cc` | Model update handler |
| `components/omnibox/browser/omnibox_field_trial.cc` | Feature flags, locale eligibility |
| `components/omnibox/common/omnibox_features.cc` | Feature definitions |

### Feature Flags

| Flag | Default | Description |
|---|---|---|
| `OmniboxOnDeviceHeadProviderNonIncognito` | ENABLED | Use OnDeviceHead in normal browsing |
| `OmniboxOnDeviceHeadProviderIncognito` | ENABLED | Use OnDeviceHead in incognito |

---

## Security & Privacy

### CRX3 Integrity

Each CRX3 file includes:
- **RSA signature** from Google (publisher proof)
- **TreeHash** (SHA-256 Merkle tree) for content integrity
- **verified_contents.json** with per-file hashes

### Privacy Considerations

- The model contains **aggregated, anonymized** search query frequency data
- No user-specific data is included
- Suggestions are generated **entirely offline** - no network requests
- The model is a snapshot of popular queries at the time of model generation
- Score values reveal relative popularity rankings of search terms in that locale

### Data Sensitivity

The 500K suggestions dataset effectively reveals:
- Top 500,000 most popular search queries per locale
- Relative popularity ranking of each query
- Cultural and linguistic search patterns per country
- Trending topics at the time of model creation (October 2024 snapshot)

---

## Tools & Files

| Tool | Description |
|---|---|
| `extract_headsuggest.py` | Full radix tree parser, exports to XLSX with metadata |
| `analyze_headsuggest.ps1` | Binary analysis (hex dump, entropy, byte frequency) |
| `download_headsuggest_all.ps1` | Downloads all available 100K locale models from Google servers |
| `chrome_headsuggest_fr_500k.xlsx` | Exported FR 500K dataset (500K rows, 24.1 MB) |
| `headsuggest_models/` | Directory with 39 CRX3 files for 100K locales + 1 CRX3 for ENUS500000 |
| `headsuggest_models/available_models.csv` | CSV with all 100K locale metadata (URLs, hashes, sizes) |
| `headsuggest_models/unavailable_locales.csv` | CSV of tested locales that returned no model |
| `headsuggest_models/extract_crx3.ps1` | PowerShell script to extract .bin files from CRX3 packages |
| `headsuggest_models/ENUS500000/` | Extracted ENUS 500K model (`cr_en-us_500000_index.bin`, 7.93 MB) |
| `headsuggest_models/cr_fr-fr_100000_index.bin` | Extracted FR-FR 100K model (1.23 MB) |

---

## Open Questions / TODO

### Not yet investigated

1. **500K tier not bulk-downloaded**: Only ENUS500000 has been downloaded and extracted. The remaining 18 500K models (~150 MB) could be downloaded using the same Omaha protocol method with `accept_locale` set to `{LOCALE}500000`.

2. **Cross-locale comparison**: No analysis has been done comparing suggestions across languages. Questions:
   - How many universal queries appear in all locales? (e.g., "youtube", "amazon", "netflix")
   - Are scores comparable across locales or independently scaled?
   - What percentage of queries in the EN model appear as transliterations in other locales?

3. **100K vs 500K content overlap**: The 100K model is presumably a subset of the 500K model (top 100K by score), but this has not been verified by extracting and comparing both tiers for the same locale.

4. **Score calibration**: The scoring system uses 23 bits (max 8,388,607) but the relationship between score values and actual search volume is unknown. Is it linear? Logarithmic? A rank-based quantization?

5. **Temporal freshness**: The model version is from October 2024. How often are models updated? Do newer Chrome versions get newer models? Is there a way to request historical versions?

6. ~~**Country-specific 500K**~~: **RESOLVED** - Country-specific 500K variants (`FRFR500000`, `DEDE500000`, etc.) are all available. 23/23 tested successfully. Sizes differ slightly from base locales (e.g., `FRFR500000` = 7.31 MB vs `FR500000` = 7.41 MB), confirming they contain locale-tuned data.

---

*Analysis performed: 2026-03-15*
*Updated: 2026-03-15 (added Chrome stable comparison, 500K tier discovery, API requirements)*
*Chrome Canary version: 148.0.7733.0*
*Chrome Stable: verified identical model*
*Model version: 20251024.824731831.14*
*Component ID: obedbbhbpmojnkanicioggnmelmoomoc*