diff --git a/src/contextual-signal-encoder/Dockerfile b/src/contextual-signal-encoder/Dockerfile
new file mode 100644
index 0000000..e18f903
--- /dev/null
+++ b/src/contextual-signal-encoder/Dockerfile
@@ -0,0 +1,7 @@
+FROM python:3.12-slim
+WORKDIR /app
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+COPY . .
+EXPOSE 8081
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8081"]
diff --git a/src/contextual-signal-encoder/README.md b/src/contextual-signal-encoder/README.md
new file mode 100644
index 0000000..760957d
--- /dev/null
+++ b/src/contextual-signal-encoder/README.md
@@ -0,0 +1,86 @@
+# Contextual Signal Encoder
+
+Reference implementation for generating contextual embedding signals conforming to the [Agentic Audiences](../../specs/v1.0/) protocol and [embedding format schema](../../specs/v1.0/embedding_format.schema.json).
+
+The [scoring service](../user-embedding-to-campaign-scoring/) consumes embeddings but the spec has no reference for **producing** them. This service fills that gap: content in, ORTB-compatible embedding out — with the spec-defined model metadata fields (`version`, `embedding_space_id`, `metric`) so the receiving party knows how to process the vector.
+
+## Public lane / private lane
+
+Ships with sentence-transformers as the "public lane" — a standardized open-source model any party can use. The `EmbeddingProvider` interface supports private-lane providers. The spec metadata fields travel with every embedding regardless of which lane produced it.
+
+## Quick Start
+
+```bash
+pip install -r requirements.txt
+uvicorn app.main:app --port 8081
+
+curl -X POST http://localhost:8081/encode \
+  -H "Content-Type: application/json" \
+  -d '{"text": "NFL playoff predictions: Chiefs vs Bills"}'
+```
+
+**Response:**
+```json
+{
+  "data": {
+    "id": "contextual-signal-encoder",
+    "name": "contextual-embeddings",
+    "segment": [{
+      "id": "ctx-a1b2c3d4",
+      "ext": {
+        "ver": "1.0",
+        "vector": [0.042, -0.118, "..."],
+        "model": "all-MiniLM-L6-v2",
+        "dimension": 384,
+        "type": "context",
+        "version": "2.0.0",
+        "embedding_space_id": "aa://spaces/contextual/sentence-transformers/minilm-l6-v2",
+        "metric": "cosine"
+      }
+    }]
+  },
+  "source": "text",
+  "content_length": 42
+}
+```
+
+The `version`, `embedding_space_id`, and `metric` fields come from `embedding_format.schema.json`. The `data` object plugs directly into the scoring service as a `user.data[]` entry.
+
+## Adding a private-lane provider
+
+```python
+from app.providers.base import EmbeddingProvider, EmbeddingResult
+
+class AcmeProvider(EmbeddingProvider):
+    async def encode_text(self, text: str) -> EmbeddingResult:
+        vector = my_model.encode(text)
+        return EmbeddingResult(
+            vector=vector.tolist(),
+            model="acme-contextual-v3",
+            version="3.1.0",
+            dimension=len(vector),
+            embedding_space_id="aa://spaces/private/acme-corp/v3",
+            metric="dot",
+        )
+    async def close(self) -> None: pass
+```
+
+## Development
+
+```bash
+pytest tests/ -v
+```
+
+```
+├── app/
+│   ├── main.py                      # FastAPI app (public lane default)
+│   ├── models/encode.py             # ORTB models using spec-defined fields
+│   ├── engine/
+│   │   ├── encoder.py               # Encoding orchestrator
+│   │   └── extractor.py             # URL text extraction
+│   ├── providers/
+│   │   ├── base.py                  # EmbeddingProvider interface
+│   │   └── sentence_transformers.py # Public lane
+│   └── routes/encode.py
+└── tests/test_encode.py
+```
diff --git a/src/contextual-signal-encoder/app/__init__.py b/src/contextual-signal-encoder/app/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/contextual-signal-encoder/app/engine/__init__.py b/src/contextual-signal-encoder/app/engine/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/contextual-signal-encoder/app/engine/encoder.py b/src/contextual-signal-encoder/app/engine/encoder.py
new file mode 100644
index 0000000..edad43b
--- /dev/null
+++ b/src/contextual-signal-encoder/app/engine/encoder.py
@@ -0,0 +1,59 @@
+"""Core encoder — content in, ORTB segment with spec-defined metadata out."""
+
+from __future__ import annotations
+
+import uuid
+
+from app.engine.extractor import extract_text_from_url
+from app.models.encode import (
+    ContextualData,
+    EmbeddingExt,
+    EncodeRequest,
+    EncodeResponse,
+    Segment,
+)
+from app.providers.base import EmbeddingProvider
+
+MAX_WORDS = 512
+
+
+class ContextualEncoder:
+
+    def __init__(self, provider: EmbeddingProvider) -> None:
+        self._provider = provider
+
+    async def encode(self, request: EncodeRequest) -> EncodeResponse:
+        if request.url:
+            text = await extract_text_from_url(request.url)
+            source = "url"
+        elif request.text:
+            text = request.text
+            source = "text"
+        else:
+            raise ValueError("Either text or url is required.")
+
+        words = text.split()
+        if len(words) > MAX_WORDS:
+            text = " ".join(words[:MAX_WORDS])
+
+        result = await self._provider.encode_text(text)
+
+        segment = Segment(
+            id=f"ctx-{uuid.uuid4().hex[:8]}",
+            name=f"contextual-{source}",
+            ext=EmbeddingExt(
+                vector=result.vector,
+                model=result.model,
+                dimension=result.dimension,
+                type="context",
+                version=result.version,
+                embedding_space_id=result.embedding_space_id,
+                metric=result.metric,
+            ),
+        )
+
+        return EncodeResponse(
+            data=ContextualData(segment=[segment]),
+            source=source,
+            content_length=len(text),
+        )
diff --git a/src/contextual-signal-encoder/app/engine/extractor.py b/src/contextual-signal-encoder/app/engine/extractor.py
new file mode 100644
index 0000000..327d875
--- /dev/null
+++ b/src/contextual-signal-encoder/app/engine/extractor.py
@@ -0,0 +1,21 @@
+"""Content extraction from URLs."""
+
+from __future__ import annotations
+
+import httpx
+from bs4 import BeautifulSoup
+
+
+async def extract_text_from_url(url: str, timeout: int = 10) -> str:
+    async with httpx.AsyncClient(timeout=timeout) as client:
+        resp = await client.get(
+            url, headers={"User-Agent": "AATech-ContextualEncoder/1.0"}, follow_redirects=True,
+        )
+        resp.raise_for_status()
+
+    soup = BeautifulSoup(resp.text, "html.parser")
+    for tag in soup(["script", "style", "nav", "footer", "header", "aside"]):
+        tag.decompose()
+
+    main = soup.find("article") or soup.find("main") or soup.find("body")
+    return (main or soup).get_text(separator=" ", strip=True)
diff --git a/src/contextual-signal-encoder/app/main.py b/src/contextual-signal-encoder/app/main.py
new file mode 100644
index 0000000..dd99814
--- /dev/null
+++ b/src/contextual-signal-encoder/app/main.py
@@ -0,0 +1,39 @@
+"""Contextual Signal Encoder — reference "public lane" implementation."""
+
+from __future__ import annotations
+
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
+
+from app.engine.encoder import ContextualEncoder
+from app.providers.sentence_transformers import SentenceTransformersProvider
+from app.routes.encode import router as encode_router, set_encoder
+
+_provider = None
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    global _provider
+    _provider = SentenceTransformersProvider()
+    set_encoder(ContextualEncoder(_provider))
+    yield
+    if _provider:
+        await _provider.close()
+
+
+app = FastAPI(
+    title="Agentic Audiences — Contextual Signal Encoder",
+    description="Reference public-lane encoder for generating contextual embeddings "
+    "with model descriptor metadata, compatible with the scoring service.",
+    version="1.0.0",
+    lifespan=lifespan,
+)
+
+app.include_router(encode_router)
+
+
+@app.get("/health")
+async def health():
+    return {"status": "ok", "lane": "public", "model": "all-MiniLM-L6-v2"}
diff --git a/src/contextual-signal-encoder/app/models/__init__.py b/src/contextual-signal-encoder/app/models/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/contextual-signal-encoder/app/models/encode.py b/src/contextual-signal-encoder/app/models/encode.py
new file mode 100644
index 0000000..ef22884
--- /dev/null
+++ b/src/contextual-signal-encoder/app/models/encode.py
@@ -0,0 +1,58 @@
+"""Models for contextual signal encoding.
+
+The output is an ORTB-compatible embedding segment using the model descriptor
+fields defined in specs/v1.0/embedding_format.schema.json — this encoder is a
+reference implementation that produces embeddings conforming to the existing spec.
+"""
+
+from __future__ import annotations
+
+from pydantic import BaseModel, Field
+
+
+class EncodeRequest(BaseModel):
+    text: str | None = Field(default=None, description="Raw text content.")
+    url: str | None = Field(default=None, description="URL to fetch and extract text from.")
+
+
+class EmbeddingExt(BaseModel):
+    """Matches the scoring service's EmbeddingSegmentExt schema.
+
+    Fields align with specs/v1.0/embedding_format.schema.json:
+    - model → model.id
+    - dimension → model.dimension
+    - type → signal type (context, identity, etc.)
+    - version → model.version
+    - embedding_space_id → model.embedding_space_id
+    - metric → model.metric
+    """
+
+    ver: str = "1.0"
+    vector: list[float]
+    model: str
+    dimension: int
+    type: str
+    version: str = Field(description="Model version (per embedding_format.schema.json).")
+    embedding_space_id: str = Field(
+        description="Embedding space URI (per embedding_format.schema.json). "
+        "Two vectors are comparable only within the same space.",
+    )
+    metric: str = Field(default="cosine", description="Similarity metric: cosine, dot, or l2.")
+
+
+class Segment(BaseModel):
+    id: str
+    name: str | None = None
+    ext: EmbeddingExt
+
+
+class ContextualData(BaseModel):
+    id: str = "contextual-signal-encoder"
+    name: str = "contextual-embeddings"
+    segment: list[Segment]
+
+
+class EncodeResponse(BaseModel):
+    data: ContextualData
+    source: str
+    content_length: int
diff --git a/src/contextual-signal-encoder/app/providers/__init__.py b/src/contextual-signal-encoder/app/providers/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/contextual-signal-encoder/app/providers/base.py b/src/contextual-signal-encoder/app/providers/base.py
new file mode 100644
index 0000000..7018ddb
--- /dev/null
+++ b/src/contextual-signal-encoder/app/providers/base.py
@@ -0,0 +1,30 @@
+"""Embedding provider interface.
+
+The public lane ships with sentence-transformers (open-source, standardized).
+The private lane is any custom provider implementing this interface.
+"""
+
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+
+
+@dataclass
+class EmbeddingResult:
+    vector: list[float]
+    model: str
+    version: str
+    dimension: int
+    embedding_space_id: str
+    metric: str = "cosine"
+
+
+class EmbeddingProvider(ABC):
+    """Interface for pluggable embedding backends (public or private lane)."""
+
+    @abstractmethod
+    async def encode_text(self, text: str) -> EmbeddingResult: ...
+
+    @abstractmethod
+    async def close(self) -> None: ...
diff --git a/src/contextual-signal-encoder/app/providers/sentence_transformers.py b/src/contextual-signal-encoder/app/providers/sentence_transformers.py
new file mode 100644
index 0000000..80cd52d
--- /dev/null
+++ b/src/contextual-signal-encoder/app/providers/sentence_transformers.py
@@ -0,0 +1,54 @@
+"""Public lane provider: sentence-transformers.
+
+This is the reference "public lane" encoder — a standardized, open-source
+model that any party can load to produce or read embeddings in a shared
+embedding space. As discussed in the working group, this provides a baseline
+for interoperability without requiring proprietary model access.
+"""
+
+from __future__ import annotations
+
+import numpy as np
+
+from app.providers.base import EmbeddingProvider, EmbeddingResult
+
+# Default public lane model and its embedding space identifier
+DEFAULT_MODEL = "all-MiniLM-L6-v2"
+DEFAULT_VERSION = "2.0.0"
+DEFAULT_SPACE = "aa://spaces/contextual/sentence-transformers/minilm-l6-v2"
+
+
+class SentenceTransformersProvider(EmbeddingProvider):
+
+    def __init__(
+        self,
+        model_name: str = DEFAULT_MODEL,
+        version: str = DEFAULT_VERSION,
+        embedding_space_id: str = DEFAULT_SPACE,
+    ) -> None:
+        self._model_name = model_name
+        self._version = version
+        self._embedding_space_id = embedding_space_id
+        self._model = None
+
+    def _load_model(self):
+        if self._model is None:
+            from sentence_transformers import SentenceTransformer
+            self._model = SentenceTransformer(self._model_name)
+        return self._model
+
+    async def encode_text(self, text: str) -> EmbeddingResult:
+        model = self._load_model()
+        embedding = model.encode(text, normalize_embeddings=True)
+        vector = np.asarray(embedding, dtype=np.float32).tolist()
+        return EmbeddingResult(
+            vector=vector,
+            model=self._model_name,
+            version=self._version,
+            dimension=len(vector),
+            embedding_space_id=self._embedding_space_id,
+            metric="cosine",
+        )
+
+    async def close(self) -> None:
+        self._model = None
diff --git a/src/contextual-signal-encoder/app/routes/__init__.py b/src/contextual-signal-encoder/app/routes/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/contextual-signal-encoder/app/routes/encode.py b/src/contextual-signal-encoder/app/routes/encode.py
new file mode 100644
index 0000000..6e3e93a
--- /dev/null
+++ b/src/contextual-signal-encoder/app/routes/encode.py
@@ -0,0 +1,33 @@
+"""Encode route."""
+
+from __future__ import annotations
+
+from fastapi import APIRouter, HTTPException
+
+from app.models.encode import EncodeRequest, EncodeResponse
+
+router = APIRouter()
+_encoder = None
+
+
+def set_encoder(encoder):
+    global _encoder
+    _encoder = encoder
+
+
+@router.post("/encode", response_model=EncodeResponse)
+async def encode_content(request: EncodeRequest) -> EncodeResponse:
+    """Generate an ORTB-compatible contextual embedding with model descriptor.
+
+    The response includes a model_descriptor envelope so the receiving party
+    knows the model name, version, embedding space, and metric needed to
+    process the vector.
+    """
+    if _encoder is None:
+        raise HTTPException(status_code=503, detail="Encoder not initialized.")
+    if not any([request.text, request.url]):
+        raise HTTPException(status_code=422, detail="Either text or url is required.")
+    try:
+        return await _encoder.encode(request)
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=f"Encoding failed: {e}")
diff --git a/src/contextual-signal-encoder/requirements.txt b/src/contextual-signal-encoder/requirements.txt
new file mode 100644
index 0000000..ad95773
--- /dev/null
+++ b/src/contextual-signal-encoder/requirements.txt
@@ -0,0 +1,9 @@
+fastapi>=0.115,<1
+uvicorn[standard]>=0.30,<1
+pydantic>=2.0,<3
+numpy>=1.26,<3
+httpx>=0.27,<1
+sentence-transformers>=3.0,<4
+beautifulsoup4>=4.12,<5
+pytest>=8.0,<9
+pytest-asyncio>=0.23,<1
diff --git a/src/contextual-signal-encoder/tests/__init__.py b/src/contextual-signal-encoder/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/contextual-signal-encoder/tests/conftest.py b/src/contextual-signal-encoder/tests/conftest.py
new file mode 100644
index 0000000..af7e479
--- /dev/null
+++ b/src/contextual-signal-encoder/tests/conftest.py
@@ -0,0 +1,6 @@
+import pytest
+
+
+@pytest.fixture
+def anyio_backend():
+    return "asyncio"
diff --git a/src/contextual-signal-encoder/tests/test_encode.py b/src/contextual-signal-encoder/tests/test_encode.py
new file mode 100644
index 0000000..27b212e
--- /dev/null
+++ b/src/contextual-signal-encoder/tests/test_encode.py
@@ -0,0 +1,133 @@
+"""Tests for the contextual signal encoder.
+
+Verifies that output conforms to:
+1. Scoring service EmbeddingSegmentExt wire format
+2. specs/v1.0/embedding_format.schema.json model metadata fields
+3. Embedding space identification for interoperability
+"""
+
+from __future__ import annotations
+
+import json
+from unittest.mock import AsyncMock, patch
+
+import numpy as np
+import pytest
+
+from app.engine.encoder import ContextualEncoder
+from app.models.encode import EncodeRequest
+from app.providers.base import EmbeddingResult
+
+
+def _mock_provider(dim: int = 384):
+    provider = AsyncMock()
+    provider.encode_text = AsyncMock(
+        return_value=EmbeddingResult(
+            vector=np.random.randn(dim).tolist(),
+            model="all-MiniLM-L6-v2",
+            version="2.0.0",
+            dimension=dim,
+            embedding_space_id="aa://spaces/contextual/sentence-transformers/minilm-l6-v2",
+            metric="cosine",
+        )
+    )
+    return provider
+
+
+class TestORTBWireFormat:
+    """Output must match the scoring service's EmbeddingSegmentExt schema."""
+
+    @pytest.mark.asyncio
+    async def test_segment_ext_fields(self):
+        encoder = ContextualEncoder(_mock_provider())
+        resp = await encoder.encode(EncodeRequest(text="NFL playoff highlights"))
+
+        ext = resp.data.segment[0].ext
+        assert ext.ver == "1.0"
+        assert ext.type == "context"
+        assert ext.model == "all-MiniLM-L6-v2"
+        assert ext.dimension == 384
+        assert len(ext.vector) == 384
+
+    @pytest.mark.asyncio
+    async def test_plugs_into_score_request(self):
+        encoder = ContextualEncoder(_mock_provider())
+        resp = await encoder.encode(EncodeRequest(text="Test"))
+
+        score_request = {
+            "id": "bid-001",
+            "user": {"id": "page", "data": [resp.data.model_dump()]},
+            "top_k": 5,
+        }
+        parsed = json.loads(json.dumps(score_request))
+        seg = parsed["user"]["data"][0]["segment"][0]
+        assert seg["ext"]["dimension"] == len(seg["ext"]["vector"])
+
+
+class TestSpecMetadata:
+    """Model metadata fields per embedding_format.schema.json."""
+
+    @pytest.mark.asyncio
+    async def test_version_present(self):
+        encoder = ContextualEncoder(_mock_provider())
+        resp = await encoder.encode(EncodeRequest(text="Test"))
+        assert resp.data.segment[0].ext.version == "2.0.0"
+
+    @pytest.mark.asyncio
+    async def test_embedding_space_id(self):
+        encoder = ContextualEncoder(_mock_provider())
+        resp = await encoder.encode(EncodeRequest(text="Test"))
+        assert resp.data.segment[0].ext.embedding_space_id == \
+            "aa://spaces/contextual/sentence-transformers/minilm-l6-v2"
+
+    @pytest.mark.asyncio
+    async def test_metric(self):
+        encoder = ContextualEncoder(_mock_provider())
+        resp = await encoder.encode(EncodeRequest(text="Test"))
+        assert resp.data.segment[0].ext.metric == "cosine"
+
+    @pytest.mark.asyncio
+    async def test_private_lane_different_space(self):
+        """A private-lane provider produces different metadata."""
+        provider = AsyncMock()
+        provider.encode_text = AsyncMock(
+            return_value=EmbeddingResult(
+                vector=np.random.randn(768).tolist(),
+                model="proprietary-model-v3",
+                version="3.1.0",
+                dimension=768,
+                embedding_space_id="aa://spaces/private/acme-corp/v3",
+                metric="dot",
+            )
+        )
+        encoder = ContextualEncoder(provider)
+        resp = await encoder.encode(EncodeRequest(text="Test"))
+        ext = resp.data.segment[0].ext
+
+        assert ext.model == "proprietary-model-v3"
+        assert ext.embedding_space_id == "aa://spaces/private/acme-corp/v3"
+        assert ext.metric == "dot"
+
+
+class TestBasicBehavior:
+
+    @pytest.mark.asyncio
+    async def test_unique_segment_ids(self):
+        encoder = ContextualEncoder(_mock_provider())
+        r1 = await encoder.encode(EncodeRequest(text="A"))
+        r2 = await encoder.encode(EncodeRequest(text="B"))
+        assert r1.data.segment[0].id != r2.data.segment[0].id
+
+    @pytest.mark.asyncio
+    async def test_empty_request_raises(self):
+        encoder = ContextualEncoder(_mock_provider())
+        with pytest.raises(ValueError):
+            await encoder.encode(EncodeRequest())
+
+    @pytest.mark.asyncio
+    async def test_url_extraction(self):
+        encoder = ContextualEncoder(_mock_provider())
+        with patch("app.engine.encoder.extract_text_from_url", new_callable=AsyncMock) as mock:
+            mock.return_value = "Extracted page content"
+            resp = await encoder.encode(EncodeRequest(url="https://example.com"))
+            assert resp.source == "url"