diff --git a/src/training/train_tinker.py b/src/training/train_tinker.py
index 7fde9bd..b9762f3 100644
--- a/src/training/train_tinker.py
+++ b/src/training/train_tinker.py
@@ -16,15 +16,20 @@
     result = train_on_tinker(config)
 """
 
+import json
 import logging
+import math
 import os
 import time
 from dataclasses import dataclass, field
 from pathlib import Path
+from types import ModuleType
 from typing import Any
 
 import yaml
 
+from src.training.tinker_data import render_chat_example
+
 logger = logging.getLogger(__name__)
 
 
@@ -150,6 +155,20 @@ def _check_sdk(self) -> bool:
         except ImportError:
             return False
 
+    def _load_tinker_module(self) -> ModuleType:
+        """Import and return the installed tinker module."""
+        return __import__("tinker")
+
+    def has_legacy_client_api(self) -> bool:
+        """Whether SDK exposes legacy Client(api_key=...) API."""
+        tinker = self._load_tinker_module()
+        return callable(getattr(tinker, "Client", None))
+
+    def has_service_client_api(self) -> bool:
+        """Whether SDK exposes ServiceClient API."""
+        tinker = self._load_tinker_module()
+        return callable(getattr(tinker, "ServiceClient", None))
+
     @property
     def is_available(self) -> bool:
         """Check if Tinker is properly configured."""
@@ -169,7 +188,14 @@ def upload_dataset(self, data_dir: Path, name: str) -> str:
         if not self._sdk_available:
             raise RuntimeError("Tinker SDK not available. Install with: pip install tinker")
 
-        tinker = __import__("tinker")  # Dynamic import to avoid static analysis errors
+        tinker = self._load_tinker_module()  # Dynamic import to avoid static analysis errors
+
+        if not self.has_legacy_client_api():
+            raise RuntimeError(
+                "Installed tinker SDK does not expose Client API required for job-style upload. "
+                "Use scripts/train_tinker.py in ServiceClient mode (default in this repo) or "
+                "install the legacy SDK variant."
+            )
 
         client = tinker.Client(api_key=self.api_key)
 
@@ -197,7 +223,12 @@ def start_training(
         if not self._sdk_available:
             raise RuntimeError("Tinker SDK not available. Install with: pip install tinker")
 
-        tinker = __import__("tinker")
+        tinker = self._load_tinker_module()
+
+        if not self.has_legacy_client_api():
+            raise RuntimeError(
+                "Installed tinker SDK does not expose Client API required for job-style training."
+            )
 
         client = tinker.Client(api_key=self.api_key)
 
@@ -228,7 +259,12 @@ def get_job_status(self, job_id: str) -> TinkerJobStatus:
         if not self._sdk_available:
             raise RuntimeError("Tinker SDK not available")
 
-        tinker = __import__("tinker")
+        tinker = self._load_tinker_module()
+
+        if not self.has_legacy_client_api():
+            raise RuntimeError(
+                "Installed tinker SDK does not expose Client API required for job status polling."
+            )
 
         client = tinker.Client(api_key=self.api_key)
         job = client.get_job(job_id)
@@ -290,7 +326,12 @@ def download_adapter(self, job_id: str, output_path: Path) -> Path:
         if not self._sdk_available:
             raise RuntimeError("Tinker SDK not available")
 
-        tinker = __import__("tinker")
+        tinker = self._load_tinker_module()
+
+        if not self.has_legacy_client_api():
+            raise RuntimeError(
+                "Installed tinker SDK does not expose Client API required for adapter download."
+            )
 
         client = tinker.Client(api_key=self.api_key)
         job = client.get_job(job_id)
@@ -346,6 +387,14 @@ def train_on_tinker(
         )
 
     try:
+        if client.has_service_client_api() and not client.has_legacy_client_api():
+            if not config.wait_for_completion:
+                return TinkerTrainingResult(
+                    success=False,
+                    error="--no-wait is not supported with the installed ServiceClient SDK mode.",
+                )
+            return _train_with_service_client_sdk(config, api_key=client.api_key)
+
         # Generate dataset name if not provided
         dataset_name = config.dataset_name or f"compression-{int(time.time())}"
 
@@ -399,6 +448,173 @@ def train_on_tinker(
         )
 
 
+def _to_sdk_datum(local_datum: Any, tinker_module: Any) -> Any:
+    """Convert local tinker_data datum to SDK Datum."""
+    target_tokens = [int(token) for token in local_datum.loss_fn_inputs["target_tokens"]]
+    weights = [float(weight) for weight in local_datum.loss_fn_inputs["weights"]]
+
+    return tinker_module.Datum(
+        model_input=tinker_module.ModelInput.from_ints(local_datum.model_input.tokens),
+        loss_fn_inputs={
+            "target_tokens": tinker_module.TensorData(data=target_tokens, dtype="int64"),
+            "weights": tinker_module.TensorData(data=weights, dtype="float32"),
+        },
+    )
+
+
+def _iter_training_batches(
+    train_file: Path,
+    tokenizer: Any,
+    tinker_module: Any,
+    batch_size: int,
+) -> Any:
+    """Yield SDK-ready training batches from chat JSONL data."""
+    batch: list[Any] = []
+
+    with open(train_file, encoding="utf-8") as f:
+        for line_number, line in enumerate(f, start=1):
+            if not line.strip():
+                continue
+
+            try:
+                record = json.loads(line)
+            except json.JSONDecodeError:
+                logger.warning("Skipping invalid JSON at line %s", line_number)
+                continue
+
+            messages = record.get("messages") if isinstance(record, dict) else None
+            if not isinstance(messages, list) or not messages:
+                logger.warning("Skipping malformed record at line %s", line_number)
+                continue
+
+            local_datum = render_chat_example(messages, tokenizer)
+            batch.append(_to_sdk_datum(local_datum, tinker_module))
+
+            if len(batch) >= batch_size:
+                yield batch
+                batch = []
+
+    if batch:
+        yield batch
+
+
+def _extract_loss(metrics: dict[str, float]) -> float | None:
+    """Extract best-effort scalar loss value from metrics dict."""
+    for key, value in metrics.items():
+        if "loss" in key.lower():
+            return float(value)
+
+    if metrics:
+        first_value = next(iter(metrics.values()))
+        return float(first_value)
+
+    return None
+
+
+def _train_with_service_client_sdk(
+    config: TinkerTrainingConfig,
+    api_key: str,
+) -> TinkerTrainingResult:
+    """Train via the modern Tinker ServiceClient/TrainingClient SDK flow."""
+    tinker = __import__("tinker")
+
+    service_client = tinker.ServiceClient(api_key=api_key)
+    training_client = service_client.create_lora_training_client(
+        base_model=config.model,
+        rank=config.lora.rank,
+    )
+    tokenizer = training_client.get_tokenizer()
+
+    train_file = config.dataset_path / "train.jsonl"
+    with open(train_file, encoding="utf-8") as train_stream:
+        total_examples = sum(1 for line in train_stream if line.strip())
+    if total_examples == 0:
+        return TinkerTrainingResult(
+            success=False, error=f"No training examples found in {train_file}"
+        )
+
+    steps_per_epoch = math.ceil(total_examples / config.batch_size)
+    total_steps = steps_per_epoch * config.epochs
+    current_step = 0
+    final_loss: float | None = None
+
+    logger.info(
+        "Starting ServiceClient training: %s examples, %s epochs, %s total steps",
+        total_examples,
+        config.epochs,
+        total_steps,
+    )
+
+    for epoch in range(1, config.epochs + 1):
+        for batch in _iter_training_batches(
+            train_file,
+            tokenizer,
+            tinker,
+            config.batch_size,
+        ):
+            fwdbwd = training_client.forward_backward(batch, "cross_entropy").result()
+            training_client.optim_step(
+                tinker.AdamParams(learning_rate=config.learning_rate),
+            ).result()
+
+            current_step += 1
+            metrics = getattr(fwdbwd, "metrics", {}) or {}
+            step_loss = _extract_loss(metrics)
+            if step_loss is not None:
+                final_loss = step_loss
+
+            if current_step % 10 == 0 or current_step == total_steps:
+                logger.info(
+                    "Epoch %s/%s Step %s/%s Loss %s",
+                    epoch,
+                    config.epochs,
+                    current_step,
+                    total_steps,
+                    f"{step_loss:.4f}" if step_loss is not None else "n/a",
+                )
+
+    if current_step == 0:
+        return TinkerTrainingResult(
+            success=False,
+            error="No valid training examples were found after parsing train.jsonl",
+        )
+
+    save_name = config.dataset_name or f"compression-{int(time.time())}"
+    save_response = training_client.save_state(save_name).result()
+    checkpoint_path = str(getattr(save_response, "path", ""))
+    info = training_client.get_info()
+    training_run_id = str(getattr(info, "model_id", "unknown"))
+
+    config.output_dir.mkdir(parents=True, exist_ok=True)
+    metadata_path = config.output_dir / "tinker_run.json"
+    metadata_path.write_text(
+        json.dumps(
+            {
+                "training_run_id": training_run_id,
+                "checkpoint_path": checkpoint_path,
+                "model": config.model,
+                "epochs": config.epochs,
+                "batch_size": config.batch_size,
+                "learning_rate": config.learning_rate,
+                "lora_rank": config.lora.rank,
+                "final_loss": final_loss,
+                "sdk_mode": "service_client",
+            },
+            indent=2,
+        ),
+        encoding="utf-8",
+    )
+
+    return TinkerTrainingResult(
+        success=True,
+        job_id=training_run_id,
+        adapter_path=config.output_dir,
+        final_loss=final_loss,
+        total_epochs=config.epochs,
+        metrics={"checkpoint_path": checkpoint_path, "metadata_path": str(metadata_path)},
+    )
+
+
 def load_config_from_yaml(config_path: Path) -> TinkerTrainingConfig:
     """
     Load Tinker training config from YAML file.
diff --git a/tests/test_train_tinker.py b/tests/test_train_tinker.py
index ece8cdc..2d90913 100644
--- a/tests/test_train_tinker.py
+++ b/tests/test_train_tinker.py
@@ -1,3 +1,5 @@
+import sys
+import types
 from pathlib import Path
 
 import pytest
@@ -17,6 +19,12 @@ def __init__(self, api_key: str | None = None):
     def is_available(self) -> bool:
         return True
 
+    def has_legacy_client_api(self) -> bool:
+        return True
+
+    def has_service_client_api(self) -> bool:
+        return False
+
     def upload_dataset(self, data_dir: Path, name: str) -> str:
         return "dataset-123"
 
@@ -48,3 +56,229 @@ def test_train_on_tinker_uses_api_key(tmp_path: Path, monkeypatch: pytest.Monkey
 
     assert result.success is True
     assert FakeClient.last_api_key == "test-key"
+
+
+def test_train_on_tinker_supports_service_client_sdk(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    data_dir = tmp_path / "training"
+    data_dir.mkdir()
+    (data_dir / "train.jsonl").write_text(
+        '{"messages":[{"role":"system","content":"s"},{"role":"user","content":"u"},{"role":"assistant","content":"a"}]}\n',
+        encoding="utf-8",
+    )
+
+    class _Future:
+        def __init__(self, value):
+            self._value = value
+
+        def result(self):
+            return self._value
+
+    class _Tokenizer:
+        def encode(self, text: str, add_special_tokens: bool = True) -> list[int]:
+            tokens = [1 for _ in text]
+            if add_special_tokens:
+                return [0] + tokens
+            return tokens
+
+    class _TrainingClient:
+        def get_tokenizer(self):
+            return _Tokenizer()
+
+        def forward_backward(self, data, loss_fn):  # noqa: ARG002
+            return _Future(types.SimpleNamespace(metrics={"loss": 0.5}, loss_fn_outputs=[]))
+
+        def optim_step(self, adam_params):  # noqa: ARG002
+            return _Future(types.SimpleNamespace(metrics={}))
+
+        def save_state(self, name: str, ttl_seconds=None):  # noqa: ARG002
+            return _Future(types.SimpleNamespace(path="tinker://run-123/weights/final"))
+
+        def get_info(self):
+            return types.SimpleNamespace(model_id="run-123")
+
+    class _ServiceClient:
+        init_kwargs = None
+
+        def __init__(self, **kwargs):  # noqa: ARG002
+            _ServiceClient.init_kwargs = kwargs
+
+        def create_lora_training_client(self, base_model: str, rank: int):  # noqa: ARG002
+            return _TrainingClient()
+
+    class _Datum:
+        def __init__(self, **kwargs):  # noqa: ARG002
+            pass
+
+    class _ModelInput:
+        @classmethod
+        def from_ints(cls, tokens):  # noqa: ARG003
+            return cls()
+
+    class _TensorData:
+        def __init__(self, **kwargs):  # noqa: ARG002
+            pass
+
+    class _AdamParams:
+        def __init__(self, **kwargs):  # noqa: ARG002
+            pass
+
+    fake_tinker = types.ModuleType("tinker")
+    fake_tinker.Client = None
+    fake_tinker.ServiceClient = _ServiceClient
+    fake_tinker.Datum = _Datum
+    fake_tinker.ModelInput = _ModelInput
+    fake_tinker.TensorData = _TensorData
+    fake_tinker.AdamParams = _AdamParams
+
+    monkeypatch.setattr(train_tinker.TinkerClient, "_check_sdk", lambda self: True)
+    monkeypatch.setitem(sys.modules, "tinker", fake_tinker)
+
+    config = train_tinker.TinkerTrainingConfig(
+        dataset_path=data_dir,
+        output_dir=tmp_path / "out",
+        wait_for_completion=True,
+        epochs=1,
+        batch_size=1,
+    )
+
+    result = train_tinker.train_on_tinker(config, api_key="test-key")
+
+    assert result.success is True
+    assert result.job_id == "run-123"
+    assert _ServiceClient.init_kwargs is not None
+    assert _ServiceClient.init_kwargs.get("api_key") == "test-key"
+
+
+def test_train_on_tinker_service_client_errors_are_captured(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    data_dir = tmp_path / "training"
+    data_dir.mkdir()
+    (data_dir / "train.jsonl").write_text(
+        '{"messages":[{"role":"system","content":"s"},{"role":"user","content":"u"},{"role":"assistant","content":"a"}]}\n',
+        encoding="utf-8",
+    )
+
+    class _ServiceModeClient:
+        def __init__(self, api_key: str | None = None):
+            self.api_key = api_key or ""
+
+        @property
+        def is_available(self) -> bool:
+            return True
+
+        def has_legacy_client_api(self) -> bool:
+            return False
+
+        def has_service_client_api(self) -> bool:
+            return True
+
+    config = train_tinker.TinkerTrainingConfig(dataset_path=data_dir)
+    monkeypatch.setattr(train_tinker, "TinkerClient", _ServiceModeClient)
+
+    def _raise_service_error(config, api_key):  # noqa: ARG001
+        raise RuntimeError("service path exploded")
+
+    monkeypatch.setattr(train_tinker, "_train_with_service_client_sdk", _raise_service_error)
+
+    result = train_tinker.train_on_tinker(config, api_key="test-key")
+
+    assert result.success is False
+    assert result.error is not None
+    assert "service path exploded" in result.error
+
+
+def test_train_on_tinker_service_client_rejects_no_valid_examples(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    data_dir = tmp_path / "training"
+    data_dir.mkdir()
+    (data_dir / "train.jsonl").write_text(
+        'not-json\n{"foo":"bar"}\n',
+        encoding="utf-8",
+    )
+
+    class _Future:
+        def __init__(self, value):
+            self._value = value
+
+        def result(self):
+            return self._value
+
+    class _Tokenizer:
+        def encode(self, text: str, add_special_tokens: bool = True) -> list[int]:
+            tokens = [1 for _ in text]
+            if add_special_tokens:
+                return [0] + tokens
+            return tokens
+
+    class _TrainingClient:
+        save_called = False
+
+        def get_tokenizer(self):
+            return _Tokenizer()
+
+        def forward_backward(self, data, loss_fn):  # noqa: ARG002
+            return _Future(types.SimpleNamespace(metrics={"loss": 0.5}, loss_fn_outputs=[]))
+
+        def optim_step(self, adam_params):  # noqa: ARG002
+            return _Future(types.SimpleNamespace(metrics={}))
+
+        def save_state(self, name: str, ttl_seconds=None):  # noqa: ARG002
+            _TrainingClient.save_called = True
+            return _Future(types.SimpleNamespace(path="tinker://run-123/weights/final"))
+
+        def get_info(self):
+            return types.SimpleNamespace(model_id="run-123")
+
+    class _ServiceClient:
+        def __init__(self, **kwargs):  # noqa: ARG002
+            pass
+
+        def create_lora_training_client(self, base_model: str, rank: int):  # noqa: ARG002
+            return _TrainingClient()
+
+    class _Datum:
+        def __init__(self, **kwargs):  # noqa: ARG002
+            pass
+
+    class _ModelInput:
+        @classmethod
+        def from_ints(cls, tokens):  # noqa: ARG003
+            return cls()
+
+    class _TensorData:
+        def __init__(self, **kwargs):  # noqa: ARG002
+            pass
+
+    class _AdamParams:
+        def __init__(self, **kwargs):  # noqa: ARG002
+            pass
+
+    fake_tinker = types.ModuleType("tinker")
+    fake_tinker.Client = None
+    fake_tinker.ServiceClient = _ServiceClient
+    fake_tinker.Datum = _Datum
+    fake_tinker.ModelInput = _ModelInput
+    fake_tinker.TensorData = _TensorData
+    fake_tinker.AdamParams = _AdamParams
+
+    monkeypatch.setattr(train_tinker.TinkerClient, "_check_sdk", lambda self: True)
+    monkeypatch.setitem(sys.modules, "tinker", fake_tinker)
+
+    config = train_tinker.TinkerTrainingConfig(
+        dataset_path=data_dir,
+        output_dir=tmp_path / "out",
+        wait_for_completion=True,
+        epochs=1,
+        batch_size=1,
+    )
+
+    result = train_tinker.train_on_tinker(config, api_key="test-key")
+
+    assert result.success is False
+    assert result.error is not None
+    assert "No valid training examples" in result.error
+    assert _TrainingClient.save_called is False