diff --git a/README.md b/README.md
index 4ddc1a2..7027895 100644
--- a/README.md
+++ b/README.md
@@ -38,6 +38,7 @@ kbench snapshot your-node        # live serving flags, for models.yaml
 
 kbench perf brain              # perf sweep only (no task authoring needed)
 kbench run brain --limit 50    # quality + perf -> results/*.json
+kbench import-verifiers brain <run-dir> --task <environment-name>
 kbench results                 # every score card recorded so far
 kbench card results/<file>     # re-render one
 ```
@@ -48,6 +49,13 @@ Raw Inspect logs land in `logs/` (gitignored). View them with:
 .venv/bin/inspect view --log-dir logs
 ```
 
+Prime Verifiers v1 `traces.jsonl` can enter the same scorecard with
+`kbench import-verifiers`. Bench reads the upstream episode artifact; it does
+not execute or copy Verifiers' harness. The importer stores episode scores,
+task-content fingerprints and short assistant excerpts, never task data, tool
+arguments or full conversations. Inspect AI remains the native runner for
+Bench tasks.
+
 ## Layout
 
 ```
@@ -58,6 +66,7 @@ kbench/
   perf.py       async load generator, any OpenAI-compatible endpoint
   results.py    the committed result schema
   run.py        orchestration: target + tasks + perf -> score card
+  verifiers_import.py  upstream Verifiers episode JSONL -> QualityResult
 data/
   public/       a few example samples, shown on the site
   private/      the real holdout — never leaves this repo
diff --git a/docs/DECISIONS.md b/docs/DECISIONS.md
index 9277a22..bc341f4 100644
--- a/docs/DECISIONS.md
+++ b/docs/DECISIONS.md
@@ -198,3 +198,33 @@ reverse-engineer the private set (D3) by probing it one sample at a time.
 **Why.** The product does not need a public code-execution service. Manual approval is the intended workflow and keeps ownership of scarce hardware and private evaluation data clear. The Lumbridge control plane stores the inert review record with status `suggested`; only an owner can advance its lifecycle.
 
 **Supersedes D8 for product behavior.** The sandbox described in D8 is no longer a launch dependency because no public suggestion is automatically executed. If automated third-party execution is ever proposed again, it requires a new explicit decision and the full D8 isolation boundary first.
+
+---
+
+## D11 — Import Verifiers episodes; do not add another harness
+
+**Decision.** Inspect AI remains Bench's native execution engine. Online Tera
+and Prime-RL evaluations run in upstream Prime Verifiers and enter Bench through
+the durable Verifiers v1 `traces.jsonl` artifact. Bench parses that artifact
+into its existing `QualityResult` and `SampleOutcome` fields; the scorecard
+schema is not changed.
+
+One Verifiers episode becomes one Bench sample. Only trainable traces contribute
+to its score, so a modeled user or judge seat does not dilute the assistant's
+result. By default the score is the mean summed weighted reward of those traces;
+a named trace metric can be selected explicitly. The card stores episode and
+trace ids, task identity hashes, reward names, pass/fail and at most the normal
+400-character assistant excerpt. It never copies task data, prompts, tool
+arguments, error messages or the full conversation.
+
+**Why.** Re-running a Verifiers environment through an Inspect-shaped adapter
+would duplicate tool-loop and multi-agent behavior and could change the thing
+being measured. The completed episode is already the evidence boundary. Bench's
+unique work is longitudinal comparison against an exact model/host target, not
+owning every runner.
+
+**Cost.** Inspect and Verifiers logs have different notions of a sample and a
+headline score. The import command therefore requires a target and task name,
+records its pass threshold and source-file digest, and labels sampling as
+Verifiers rather than pretending Inspect produced it. Comparability still
+requires the same target snapshot, task fingerprint, score source and threshold.
diff --git a/kbench/cli.py b/kbench/cli.py
index fc1b3ca..4a43828 100644
--- a/kbench/cli.py
+++ b/kbench/cli.py
@@ -12,11 +12,12 @@ from rich.console import Console
 from rich.table import Table
 
 from . import tasks as task_catalog
-from .compare import compare as compare_runs, direction
-from .sweep import analyse, point_from_run
+from .compare import compare as compare_runs
+from .compare import direction
 from .registry import load_registry
 from .results import RESULTS_DIR, Run
 from .run import build_run, run_perf, run_quality
+from .sweep import analyse, point_from_run
 
 app = typer.Typer(
     add_completion=False,
@@ -307,6 +308,51 @@ def card_cmd(path: Path) -> None:
     _print_card_dict(data)
 
 
+@app.command("import-verifiers")
+def import_verifiers_cmd(
+    target: str = typer.Argument(..., help="registered model/host target that produced the traces"),
+    path: Path = typer.Argument(..., help="Verifiers run directory or traces.jsonl"),
+    task: str = typer.Option(..., help="Bench task name for this imported environment"),
+    tier: str = typer.Option("signal", help="reference | signal | canary"),
+    pass_threshold: float = typer.Option(1.0, help="score required for an episode to pass"),
+    primary_metric: str | None = typer.Option(
+        None, help="trace metric to import; defaults to summed weighted rewards"
+    ),
+    save: bool = typer.Option(True, help="write the existing results/*.json scorecard"),
+) -> None:
+    """Import upstream Verifiers episodes; execute no model and no harness."""
+    from .verifiers_import import FORMAT, VerifiersImportError, import_quality, source_sha256
+
+    registry = load_registry()
+    registered = registry.target(target)
+    try:
+        quality = import_quality(
+            path,
+            task=task,
+            tier=tier,
+            pass_threshold=pass_threshold,
+            primary_metric=primary_metric,
+        )
+        digest = source_sha256(path)
+    except VerifiersImportError as exc:
+        raise typer.BadParameter(str(exc), param_hint="path") from exc
+
+    run = build_run(registry, registered, quality=[quality], perf=None)
+    run.runner["quality_import"] = {
+        "format": FORMAT,
+        "source_sha256": digest,
+    }
+    run.sampling = {
+        "source": "verifiers",
+        "primary_metric": primary_metric,
+        "pass_threshold": pass_threshold,
+    }
+    _print_card(run)
+    if save:
+        saved = run.save()
+        console.print(f"\n[green]saved[/green] {saved.relative_to(Path.cwd())}")
+
+
 def _print_card(run: Run) -> None:
     _print_card_dict(run.to_dict())
 
diff --git a/kbench/verifiers_import.py b/kbench/verifiers_import.py
new file mode 100644
index 0000000..d0bbdab
--- /dev/null
+++ b/kbench/verifiers_import.py
@@ -0,0 +1,287 @@
+"""Import Prime Verifiers v1 episode JSONL into Bench's existing scorecard.
+
+Verifiers owns rollout execution and its trace schema. Bench reads the durable
+``traces.jsonl`` artifact with the standard library, reduces one episode to one
+sample outcome, and keeps its own result schema unchanged. Raw prompts, task
+data, tool arguments and full conversations never enter the committed card.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import json
+from pathlib import Path
+from typing import Any
+
+from .results import QualityResult, SampleOutcome, truncate
+
+FORMAT = "verifiers-v1-episode-jsonl"
+
+
+class VerifiersImportError(ValueError):
+    pass
+
+
+def traces_path(path: str | Path) -> Path:
+    candidate = Path(path)
+    if candidate.is_dir():
+        candidate = candidate / "traces.jsonl"
+    if not candidate.is_file():
+        raise VerifiersImportError(f"Verifiers traces file not found: {candidate}")
+    return candidate
+
+
+def source_sha256(path: str | Path) -> str:
+    return hashlib.sha256(traces_path(path).read_bytes()).hexdigest()
+
+
+def _reward_value(rewards: Any) -> tuple[float | None, list[str]]:
+    if not isinstance(rewards, dict):
+        return None, []
+    total = 0.0
+    found = False
+    names: list[str] = []
+    for name, reward in sorted(rewards.items()):
+        if reward is None:
+            continue
+        if isinstance(reward, (int, float)) and not isinstance(reward, bool):
+            score, weight = float(reward), 1.0
+        elif isinstance(reward, dict) and isinstance(reward.get("score"), (int, float)):
+            score = float(reward["score"])
+            weight = float(reward.get("weight", 1.0))
+        else:
+            continue
+        found = True
+        names.append(str(name))
+        total += score * weight
+    return (total if found else None), names
+
+
+def _trace_value(trace: dict[str, Any], primary_metric: str | None) -> tuple[float | None, list[str]]:
+    if primary_metric:
+        metrics = trace.get("metrics") or {}
+        value = metrics.get(primary_metric) if isinstance(metrics, dict) else None
+        if isinstance(value, (int, float)) and not isinstance(value, bool):
+            return float(value), [primary_metric]
+        return None, []
+    return _reward_value(trace.get("rewards"))
+
+
+def _content_text(content: Any) -> str:
+    if isinstance(content, str):
+        return content
+    if isinstance(content, list):
+        parts: list[str] = []
+        for part in content:
+            if isinstance(part, str):
+                parts.append(part)
+            elif isinstance(part, dict) and isinstance(part.get("text"), str):
+                parts.append(part["text"])
+        return "".join(parts)
+    return ""
+
+
+def _last_assistant_text(trace: dict[str, Any]) -> str | None:
+    for node in reversed(trace.get("nodes") or []):
+        if not isinstance(node, dict):
+            continue
+        message = node.get("message") or {}
+        if isinstance(message, dict) and message.get("role") == "assistant":
+            text = _content_text(message.get("content")).strip()
+            if text:
+                return text
+    completion = trace.get("completion")
+    return completion.strip() if isinstance(completion, str) and completion.strip() else None
+
+
+def _eligible_traces(episode: dict[str, Any]) -> list[dict[str, Any]]:
+    traces = episode.get("traces")
+    if not isinstance(traces, list):
+        raise VerifiersImportError("episode field 'traces' must be a list")
+    typed = [trace for trace in traces if isinstance(trace, dict)]
+    trainable = [
+        trace
+        for trace in typed
+        if (trace.get("agent") or {}).get("trainable", True) is not False
+    ]
+    # Eval files from older v1 builds may omit trainable. If an env explicitly
+    # marks every trace non-trainable, keep the traces rather than manufacturing
+    # an empty sample.
+    return trainable or typed
+
+
+def _task_identity(episode: dict[str, Any]) -> str:
+    task = episode.get("task") or {}
+    if not isinstance(task, dict):
+        task = {}
+    durable = task.get("key") or task.get("hash")
+    if durable:
+        return str(durable)
+    # Hash task data locally if an older trace lacks key/hash. The card receives
+    # only this digest; private task content is never copied into it.
+    canonical = json.dumps(task.get("data"), sort_keys=True, separators=(",", ":"))
+    return hashlib.sha256(canonical.encode()).hexdigest()
+
+
+def _dataset_fingerprint(episodes: list[dict[str, Any]]) -> str | None:
+    if not episodes:
+        return None
+    identities = [
+        f"{(episode.get('env') or {}).get('id', '')}\x1f{_task_identity(episode)}"
+        for episode in episodes
+    ]
+    digest = hashlib.sha256()
+    for identity in sorted(identities):
+        digest.update(identity.encode())
+        digest.update(b"\x1e")
+    return f"sha256:{digest.hexdigest()[:16]}"
+
+
+def _duration(episodes: list[dict[str, Any]]) -> float | None:
+    total = 0.0
+    measured = False
+    for episode in episodes:
+        starts: list[float] = []
+        ends: list[float] = []
+        for trace in episode.get("traces") or []:
+            timing = trace.get("timing") if isinstance(trace, dict) else None
+            if not isinstance(timing, dict):
+                continue
+            for span in timing.values():
+                if not isinstance(span, dict):
+                    continue
+                start, end = span.get("start"), span.get("end")
+                if isinstance(start, (int, float)) and start > 0:
+                    starts.append(float(start))
+                if isinstance(end, (int, float)) and end > 0:
+                    ends.append(float(end))
+        if starts and ends and max(ends) >= min(starts):
+            total += max(ends) - min(starts)
+            measured = True
+    return round(total, 6) if measured else None
+
+
+def read_episodes(path: str | Path) -> list[dict[str, Any]]:
+    source = traces_path(path)
+    episodes: list[dict[str, Any]] = []
+    ids: set[str] = set()
+    for line_number, line in enumerate(source.read_text().splitlines(), start=1):
+        if not line.strip():
+            continue
+        try:
+            episode = json.loads(line)
+        except json.JSONDecodeError as exc:
+            raise VerifiersImportError(f"{source}:{line_number}: invalid JSON: {exc.msg}") from exc
+        if not isinstance(episode, dict):
+            raise VerifiersImportError(f"{source}:{line_number}: episode must be an object")
+        episode_id = str(episode.get("id") or "")
+        if not episode_id:
+            raise VerifiersImportError(f"{source}:{line_number}: episode has no id")
+        if episode_id in ids:
+            raise VerifiersImportError(f"{source}:{line_number}: duplicate episode id {episode_id!r}")
+        ids.add(episode_id)
+        _eligible_traces(episode)  # validate the durable v1 boundary now
+        episodes.append(episode)
+    if not episodes:
+        raise VerifiersImportError(f"{source} contains no episodes")
+    return episodes
+
+
+def import_quality(
+    path: str | Path,
+    task: str,
+    tier: str = "signal",
+    pass_threshold: float = 1.0,
+    primary_metric: str | None = None,
+) -> QualityResult:
+    """Reduce Verifiers episodes to one existing Bench QualityResult."""
+    if tier not in {"reference", "signal", "canary"}:
+        raise VerifiersImportError("tier must be reference, signal or canary")
+    episodes = read_episodes(path)
+    outcomes: list[SampleOutcome] = []
+    versions: set[str] = set()
+
+    for episode in episodes:
+        traces = _eligible_traces(episode)
+        values: list[float] = []
+        reward_names: set[str] = set()
+        excerpts: list[str] = []
+        trace_ids: list[str] = []
+        agents: list[str] = []
+        trace_ok = True
+        error_types = {
+            str(error.get("type"))
+            for error in (episode.get("errors") or [])
+            if isinstance(error, dict) and error.get("type")
+        }
+        for trace in traces:
+            value, names = _trace_value(trace, primary_metric)
+            if value is not None:
+                values.append(value)
+            reward_names.update(names)
+            trace_ids.append(str(trace.get("id") or ""))
+            agent = trace.get("agent") or {}
+            agents.append(str(agent.get("name") or "agent"))
+            trace_ok = trace_ok and bool(trace.get("ok", False))
+            verifiers = trace.get("verifiers") or {}
+            if isinstance(verifiers, dict) and verifiers.get("version"):
+                versions.add(str(verifiers["version"]))
+            error_types.update(
+                str(error.get("type"))
+                for error in (trace.get("errors") or [])
+                if isinstance(error, dict) and error.get("type")
+            )
+            text = _last_assistant_text(trace)
+            if text:
+                excerpts.append(f"{agents[-1]}: {text}" if len(traces) > 1 else text)
+
+        score = sum(values) / len(values) if values else 0.0
+        episode_ok = bool(episode.get("ok", False)) and trace_ok
+        outcomes.append(
+            SampleOutcome(
+                sample_id=str(episode["id"]),
+                score=round(score, 6),
+                passed=episode_ok and score >= pass_threshold,
+                excerpt=truncate("\n\n".join(excerpts) or None),
+                metadata={
+                    "source": FORMAT,
+                    "env": str((episode.get("env") or {}).get("id") or ""),
+                    "task_key": _task_identity(episode),
+                    "trace_ids": trace_ids,
+                    "agents": agents,
+                    "episode_ok": episode_ok,
+                    "score_source": f"metric:{primary_metric}" if primary_metric else "weighted_rewards",
+                    "reward_names": sorted(reward_names),
+                    "error_types": sorted(error_types),
+                    "ungraded": not values,
+                },
+            )
+        )
+
+    accuracy = sum(outcome.passed for outcome in outcomes) / len(outcomes)
+    mean_score = sum(outcome.score for outcome in outcomes) / len(outcomes)
+    metrics = {
+        "accuracy": round(accuracy, 6),
+        "mean_score": round(mean_score, 6),
+        "pass_threshold": float(pass_threshold),
+    }
+    return QualityResult(
+        task=task,
+        tier=tier,
+        dataset_version=("verifiers:" + ",".join(sorted(versions))) if versions else None,
+        dataset_fingerprint=_dataset_fingerprint(episodes),
+        n_samples=len(episodes),
+        metrics=metrics,
+        samples=outcomes,
+        duration_s=_duration(episodes),
+    )
+
+
+__all__ = [
+    "FORMAT",
+    "VerifiersImportError",
+    "import_quality",
+    "read_episodes",
+    "source_sha256",
+    "traces_path",
+]
diff --git a/tests/test_verifiers_import.py b/tests/test_verifiers_import.py
new file mode 100644
index 0000000..38b3f96
--- /dev/null
+++ b/tests/test_verifiers_import.py
@@ -0,0 +1,122 @@
+"""Prime Verifiers v1 episode JSONL enters Bench without a second harness."""
+
+from __future__ import annotations
+
+import json
+import sys
+import tempfile
+import unittest
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parent.parent
+sys.path.insert(0, str(ROOT))
+
+from kbench.verifiers_import import (
+    VerifiersImportError,
+    import_quality,
+    read_episodes,
+)
+
+
+def trace(
+    trace_id: str,
+    reward: float,
+    *,
+    agent: str = "agent",
+    trainable: bool = True,
+    answer: str = "done",
+) -> dict:
+    return {
+        "id": trace_id,
+        "verifiers": {"version": "0.3.1"},
+        "agent": {"name": agent, "trainable": trainable},
+        "ok": True,
+        "rewards": {"task": {"score": reward, "weight": 1.0}},
+        "metrics": {"strict": reward},
+        "nodes": [{"message": {"role": "assistant", "content": answer}}],
+        "timing": {"agent": {"start": 10.0, "end": 12.0}},
+    }
+
+
+def episode(episode_id: str, traces: list[dict], task_key: str = "task-1") -> dict:
+    return {
+        "id": episode_id,
+        "env": {"id": "example-tool-loop-v1"},
+        "task": {
+            "type": "OfficeJobTask",
+            "key": task_key,
+            "data": {"private_prompt": "must never enter the score card"},
+        },
+        "ok": True,
+        "errors": [],
+        "traces": traces,
+    }
+
+
+class VerifiersImportTests(unittest.TestCase):
+    def write(self, root: Path, rows: list[dict]) -> Path:
+        path = root / "traces.jsonl"
+        path.write_text("".join(json.dumps(row) + "\n" for row in rows))
+        return path
+
+    def test_one_episode_becomes_one_existing_sample_outcome(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = self.write(Path(tmp), [episode("ep-1", [trace("tr-1", 1.0)])])
+            result = import_quality(path, "example-tool-loop")
+        self.assertEqual(result.n_samples, 1)
+        self.assertEqual(result.metrics["accuracy"], 1.0)
+        self.assertEqual(result.samples[0].sample_id, "ep-1")
+        self.assertEqual(result.samples[0].excerpt, "done")
+        self.assertNotIn("private_prompt", json.dumps(result.samples[0].metadata))
+        self.assertEqual(result.dataset_version, "verifiers:0.3.1")
+
+    def test_multi_agent_episode_ignores_non_trainable_user_simulator(self) -> None:
+        rows = [
+            episode(
+                "ep-1",
+                [
+                    trace("assistant", 0.75, agent="assistant"),
+                    trace("user", 0.0, agent="user", trainable=False),
+                ],
+            )
+        ]
+        with tempfile.TemporaryDirectory() as tmp:
+            result = import_quality(self.write(Path(tmp), rows), "user-sim", pass_threshold=0.5)
+        self.assertEqual(result.samples[0].score, 0.75)
+        self.assertTrue(result.samples[0].passed)
+        self.assertEqual(result.samples[0].metadata["agents"], ["assistant"])
+
+    def test_named_metric_can_be_the_score_source(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = self.write(Path(tmp), [episode("ep-1", [trace("tr-1", 0.25)])])
+            result = import_quality(path, "strict", pass_threshold=0.2, primary_metric="strict")
+        self.assertEqual(result.samples[0].score, 0.25)
+        self.assertEqual(result.samples[0].metadata["score_source"], "metric:strict")
+
+    def test_fingerprint_uses_task_identity_not_line_order(self) -> None:
+        rows = [
+            episode("ep-1", [trace("tr-1", 1.0)], "a"),
+            episode("ep-2", [trace("tr-2", 0.0)], "b"),
+        ]
+        with tempfile.TemporaryDirectory() as tmp:
+            root = Path(tmp)
+            a = import_quality(self.write(root, rows), "t").dataset_fingerprint
+            b = import_quality(self.write(root, list(reversed(rows))), "t").dataset_fingerprint
+        self.assertEqual(a, b)
+
+    def test_duplicate_episode_ids_are_refused(self) -> None:
+        row = episode("same", [trace("tr-1", 1.0)])
+        with tempfile.TemporaryDirectory() as tmp:
+            path = self.write(Path(tmp), [row, row])
+            with self.assertRaises(VerifiersImportError):
+                read_episodes(path)
+
+    def test_directory_resolves_the_upstream_traces_filename(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            root = Path(tmp)
+            self.write(root, [episode("ep-1", [trace("tr-1", 1.0)])])
+            self.assertEqual(len(read_episodes(root)), 1)
+
+
+if __name__ == "__main__":
+    unittest.main()