diff --git a/WORK-RECORDS.md b/WORK-RECORDS.md
index ddbca14..2338d79 100644
--- a/WORK-RECORDS.md
+++ b/WORK-RECORDS.md
@@ -17,5 +17,5 @@
 | task | GLAS-WP-0001-T02 | done | — | workplans/GLAS-WP-0001-harness-router-foundation.md |
 | task | GLAS-WP-0001-T03 | done | — | workplans/GLAS-WP-0001-harness-router-foundation.md |
 | task | GLAS-WP-0001-T04 | progress | — | workplans/GLAS-WP-0001-harness-router-foundation.md |
-| task | GLAS-WP-0001-T05 | todo | — | workplans/GLAS-WP-0001-harness-router-foundation.md |
+| task | GLAS-WP-0001-T05 | progress | — | workplans/GLAS-WP-0001-harness-router-foundation.md |
 | task | GLAS-WP-0001-T06 | done | — | workplans/GLAS-WP-0001-harness-router-foundation.md |
diff --git a/registry/reins/rein-openweights.yaml b/registry/reins/rein-openweights.yaml
index f26cccd..93e0db7 100644
--- a/registry/reins/rein-openweights.yaml
+++ b/registry/reins/rein-openweights.yaml
@@ -2,12 +2,15 @@ id: rein-openweights
 title: OpenRouter open-weight agentic loop
 description: >
   Agentic tool-use harness driving current open-weight models via
-  OpenRouter/llm-connect, as an alternative to frontier-vendor CLIs.
-  Chartered by ADR-001; not yet implementing this contract.
+  OpenRouter (own minimal client, not llm-connect — see
+  rein-openweights/workplans/REIN-OW-WP-0001-T01), as an alternative to
+  frontier-vendor CLIs. Chartered by ADR-001.
 handler: glas_harness.reins.rein_openweights:ReinOpenWeights
 capabilities:
   session_style: unattended
   model_class: open-weight
-  credential_source: tbd
-  # tbd: resolved by GLAS-WP-0001-T06 before this rein is implemented.
-status: planned
+  credential_source: rein-local
+  # rein-local per ADR-002 (Option B): rein-openweights acquires its own
+  # OpenRouter credential (OpenBao, or OPENROUTER_API_KEY env var).
+  # glas-harness does not broker it.
+status: implemented
diff --git a/src/glas_harness/reins/_shared.py b/src/glas_harness/reins/_shared.py
new file mode 100644
index 0000000..a164496
--- /dev/null
+++ b/src/glas_harness/reins/_shared.py
@@ -0,0 +1,28 @@
+"""Shared helpers for reins that implement the contract by shelling out to a CLI."""
+
+from __future__ import annotations
+
+import json
+import subprocess
+import tempfile
+from pathlib import Path
+from typing import Any
+
+
+def git_head(repo: str) -> str:
+    proc = subprocess.run(
+        ["git", "-C", str(Path(repo).expanduser()), "rev-parse", "HEAD"],
+        capture_output=True,
+        text=True,
+    )
+    return proc.stdout.strip() if proc.returncode == 0 else ""
+
+
+def write_task_file(title: str, description: str, target_repo: str, **extra: Any) -> str:
+    task_spec = {"title": title, "description": description, "target_repo": target_repo, **extra}
+    fd = tempfile.NamedTemporaryFile(
+        mode="w", suffix=".json", prefix="glas-harness-task-", delete=False
+    )
+    json.dump(task_spec, fd)
+    fd.close()
+    return fd.name
diff --git a/src/glas_harness/reins/rein_aharness.py b/src/glas_harness/reins/rein_aharness.py
index f5f4f64..fd72054 100644
--- a/src/glas_harness/reins/rein_aharness.py
+++ b/src/glas_harness/reins/rein_aharness.py
@@ -12,14 +12,12 @@ end + sandbox handoff), not fine-grained tool interception yet.
 
 from __future__ import annotations
 
-import json
 import shutil
 import subprocess
-import tempfile
-from pathlib import Path
 from typing import Any
 
 from glas_harness.contract import Rein, SandboxHandle, ToolCall, ToolResult
+from glas_harness.reins._shared import git_head, write_task_file
 
 
 class ReinAharnessNotInstalled(RuntimeError):
@@ -49,26 +47,15 @@ class ReinAharness(Rein):
         if not target_repo:
             raise ValueError("no target_repo resolvable from inputs or sandbox reachability")
 
-        task_file = inputs.get("task_file")
-        if not task_file:
-            task_spec = {
-                "title": inputs["title"],
-                "description": inputs["description"],
-                "target_repo": target_repo,
-                "agent": inputs.get("agent", "coach"),
-            }
-            fd = tempfile.NamedTemporaryFile(
-                mode="w", suffix=".json", prefix="glas-harness-task-", delete=False
-            )
-            json.dump(task_spec, fd)
-            fd.close()
-            task_file = fd.name
+        task_file = inputs.get("task_file") or write_task_file(
+            inputs["title"], inputs["description"], target_repo, agent=inputs.get("agent", "coach")
+        )
 
         return {
             "sandbox_id": sandbox.sandbox_id,
             "task_file": task_file,
             "target_repo": target_repo,
-            "head_before": self._git_head(target_repo),
+            "head_before": git_head(target_repo),
         }
 
     def dispatch_tool(self, session: dict[str, str], tool_call: ToolCall) -> ToolResult:
@@ -85,18 +72,9 @@ class ReinAharness(Rein):
         return ToolResult(ok=ok, output=proc.stdout, error=None if ok else proc.stderr)
 
     def end_session(self, session: dict[str, str]) -> dict[str, str]:
-        head_after = self._git_head(session["target_repo"])
+        head_after = git_head(session["target_repo"])
         committed = bool(head_after) and head_after != session.get("head_before")
         return {
             "commit_sha": head_after or "",
             "committed": str(committed),
         }
-
-    @staticmethod
-    def _git_head(repo: str) -> str:
-        proc = subprocess.run(
-            ["git", "-C", str(Path(repo).expanduser()), "rev-parse", "HEAD"],
-            capture_output=True,
-            text=True,
-        )
-        return proc.stdout.strip() if proc.returncode == 0 else ""
diff --git a/src/glas_harness/reins/rein_openweights.py b/src/glas_harness/reins/rein_openweights.py
new file mode 100644
index 0000000..bdbcc8a
--- /dev/null
+++ b/src/glas_harness/reins/rein_openweights.py
@@ -0,0 +1,73 @@
+"""ReinOpenWeights — glas-harness adapter around the rein-openweights CLI.
+
+Same shape as reins/rein_aharness.py: rein-openweights's `run` command
+performs an entire bounded agentic session (credential acquisition,
+OpenRouter tool-calling loop, commit verification) as one opaque unit —
+no per-tool-call hooks exposed yet. dispatch_tool collapses the whole
+run into a single call.
+"""
+
+from __future__ import annotations
+
+import shutil
+import subprocess
+from typing import Any
+
+from glas_harness.contract import Rein, SandboxHandle, ToolCall, ToolResult
+from glas_harness.reins._shared import git_head, write_task_file
+
+
+class ReinOpenWeightsNotInstalled(RuntimeError):
+    pass
+
+
+class ReinOpenWeights(Rein):
+    def __init__(self, cli_bin: str = "rein-openweights", model: str | None = None) -> None:
+        self.cli_bin = cli_bin
+        self.model = model
+
+    def _bin(self) -> str:
+        resolved = shutil.which(self.cli_bin)
+        if not resolved:
+            raise ReinOpenWeightsNotInstalled(
+                f"'{self.cli_bin}' not found on PATH — install rein-openweights first"
+            )
+        return resolved
+
+    def start_session(
+        self, profile: dict[str, Any], inputs: dict[str, str], sandbox: SandboxHandle
+    ) -> dict[str, str]:
+        target_repo = (
+            inputs.get("target_repo")
+            or sandbox.reachability.get("workspace_dir")
+            or sandbox.reachability.get("remote_dir")
+        )
+        if not target_repo:
+            raise ValueError("no target_repo resolvable from inputs or sandbox reachability")
+
+        task_file = inputs.get("task_file") or write_task_file(
+            inputs["title"], inputs["description"], target_repo
+        )
+
+        return {
+            "sandbox_id": sandbox.sandbox_id,
+            "task_file": task_file,
+            "target_repo": target_repo,
+            "head_before": git_head(target_repo),
+        }
+
+    def dispatch_tool(self, session: dict[str, str], tool_call: ToolCall) -> ToolResult:
+        argv = [self._bin(), "run", "--task-file", session["task_file"], "--no-hub"]
+        if self.model:
+            argv += ["--model", self.model]
+        proc = subprocess.run(argv, capture_output=True, text=True)
+        ok = proc.returncode == 0
+        return ToolResult(ok=ok, output=proc.stdout, error=None if ok else proc.stderr)
+
+    def end_session(self, session: dict[str, str]) -> dict[str, str]:
+        head_after = git_head(session["target_repo"])
+        committed = bool(head_after) and head_after != session.get("head_before")
+        return {
+            "commit_sha": head_after or "",
+            "committed": str(committed),
+        }
diff --git a/tests/test_rein_aharness.py b/tests/test_rein_aharness.py
index 7f2e2ef..c0176c3 100644
--- a/tests/test_rein_aharness.py
+++ b/tests/test_rein_aharness.py
@@ -80,8 +80,10 @@ def test_end_session_detects_new_commit(tmp_path) -> None:
     subprocess.run(["git", "init", "-q"], cwd=repo, check=True)
     subprocess.run(["git", "commit", "-q", "--allow-empty", "-m", "init"], cwd=repo, check=True)
 
+    from glas_harness.reins._shared import git_head
+
     rein = ReinAharness()
-    head_before = rein._git_head(str(repo))
+    head_before = git_head(str(repo))
 
     subprocess.run(["git", "commit", "-q", "--allow-empty", "-m", "task"], cwd=repo, check=True)
 
@@ -96,8 +98,10 @@ def test_end_session_no_new_commit(tmp_path) -> None:
     subprocess.run(["git", "init", "-q"], cwd=repo, check=True)
     subprocess.run(["git", "commit", "-q", "--allow-empty", "-m", "init"], cwd=repo, check=True)
 
+    from glas_harness.reins._shared import git_head
+
     rein = ReinAharness()
-    head = rein._git_head(str(repo))
+    head = git_head(str(repo))
 
     summary = rein.end_session({"target_repo": str(repo), "head_before": head})
     assert summary["committed"] == "False"
diff --git a/tests/test_rein_openweights.py b/tests/test_rein_openweights.py
new file mode 100644
index 0000000..8c4d927
--- /dev/null
+++ b/tests/test_rein_openweights.py
@@ -0,0 +1,106 @@
+import json
+import subprocess
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from glas_harness.contract import Rein, SandboxHandle, ToolCall
+from glas_harness.reins.rein_openweights import ReinOpenWeights, ReinOpenWeightsNotInstalled
+
+
+def test_is_rein_subclass() -> None:
+    assert issubclass(ReinOpenWeights, Rein)
+
+
+def test_bin_raises_if_not_installed() -> None:
+    rein = ReinOpenWeights(cli_bin="does-not-exist-binary")
+    with pytest.raises(ReinOpenWeightsNotInstalled):
+        rein._bin()
+
+
+def test_start_session_writes_task_file_and_captures_head(tmp_path) -> None:
+    repo = tmp_path / "repo"
+    repo.mkdir()
+    subprocess.run(["git", "init", "-q"], cwd=repo, check=True)
+    subprocess.run(["git", "commit", "-q", "--allow-empty", "-m", "init"], cwd=repo, check=True)
+
+    rein = ReinOpenWeights()
+    sandbox = SandboxHandle(sandbox_id="abc", host="localhost", reachability={"workspace_dir": str(repo)})
+    session = rein.start_session(
+        profile={"id": "harness.agent-dev-local"},
+        inputs={"title": "t", "description": "d"},
+        sandbox=sandbox,
+    )
+
+    assert session["target_repo"] == str(repo)
+    assert session["head_before"]
+    task_spec = json.loads(open(session["task_file"]).read())
+    assert task_spec["title"] == "t"
+    assert task_spec["target_repo"] == str(repo)
+
+
+def test_start_session_requires_resolvable_target_repo() -> None:
+    rein = ReinOpenWeights()
+    sandbox = SandboxHandle(sandbox_id="abc", host="localhost", reachability={})
+    with pytest.raises(ValueError, match="target_repo"):
+        rein.start_session(profile={}, inputs={"title": "t", "description": "d"}, sandbox=sandbox)
+
+
+def test_dispatch_tool_invokes_rein_openweights_cli() -> None:
+    rein = ReinOpenWeights()
+    session = {"task_file": "/tmp/task.json"}
+
+    fake_result = MagicMock(returncode=0, stdout="ok", stderr="")
+    with patch.object(rein, "_bin", return_value="/usr/bin/rein-openweights"):
+        with patch("glas_harness.reins.rein_openweights.subprocess.run", return_value=fake_result) as run:
+            result = rein.dispatch_tool(session, ToolCall(name="run_task"))
+
+    argv = run.call_args.args[0]
+    assert argv[:3] == ["/usr/bin/rein-openweights", "run", "--task-file"]
+    assert "--no-hub" in argv
+    assert result.ok is True
+    assert result.output == "ok"
+
+
+def test_dispatch_tool_passes_model_when_set() -> None:
+    rein = ReinOpenWeights(model="meta-llama/llama-3.1-70b-instruct")
+    session = {"task_file": "/tmp/task.json"}
+    fake_result = MagicMock(returncode=0, stdout="ok", stderr="")
+
+    with patch.object(rein, "_bin", return_value="/usr/bin/rein-openweights"):
+        with patch("glas_harness.reins.rein_openweights.subprocess.run", return_value=fake_result) as run:
+            rein.dispatch_tool(session, ToolCall(name="run_task"))
+
+    argv = run.call_args.args[0]
+    assert "--model" in argv
+    assert "meta-llama/llama-3.1-70b-instruct" in argv
+
+
+def test_dispatch_tool_reports_failure() -> None:
+    rein = ReinOpenWeights()
+    session = {"task_file": "/tmp/task.json"}
+
+    fake_result = MagicMock(returncode=1, stdout="", stderr="boom")
+    with patch.object(rein, "_bin", return_value="/usr/bin/rein-openweights"):
+        with patch("glas_harness.reins.rein_openweights.subprocess.run", return_value=fake_result):
+            result = rein.dispatch_tool(session, ToolCall(name="run_task"))
+
+    assert result.ok is False
+    assert result.error == "boom"
+
+
+def test_end_session_detects_new_commit(tmp_path) -> None:
+    repo = tmp_path / "repo"
+    repo.mkdir()
+    subprocess.run(["git", "init", "-q"], cwd=repo, check=True)
+    subprocess.run(["git", "commit", "-q", "--allow-empty", "-m", "init"], cwd=repo, check=True)
+
+    rein = ReinOpenWeights()
+    from glas_harness.reins._shared import git_head
+
+    head_before = git_head(str(repo))
+    subprocess.run(["git", "commit", "-q", "--allow-empty", "-m", "task"], cwd=repo, check=True)
+
+    summary = rein.end_session({"target_repo": str(repo), "head_before": head_before})
+    assert summary["committed"] == "True"
+    assert summary["commit_sha"] != head_before
diff --git a/workplans/GLAS-WP-0001-harness-router-foundation.md b/workplans/GLAS-WP-0001-harness-router-foundation.md
index ea185bc..d710a04 100644
--- a/workplans/GLAS-WP-0001-harness-router-foundation.md
+++ b/workplans/GLAS-WP-0001-harness-router-foundation.md
@@ -103,16 +103,19 @@ is pushed — coordinate repo creation with the operator.
 `rein-openweights/REIN-OW-WP-0001` (T01-T04) is done: standalone agentic
 loop, own OpenRouter client (not llm-connect — see that workplan's T01
 for why), tool surface, credential acquisition, commit-verified success
-+ hub reporting, 26 tests. **Not yet done here:** a
-`glas_harness/reins/rein_openweights.py` adapter implementing the `Rein`
-ABC and shelling out to `rein-openweights run`, mirroring
-`reins/rein_aharness.py` — that's the piece that actually plugs this
-rein into glas-harness's gateway. registry/reins/rein-openweights.yaml's
-`status: planned` should flip to `implemented` once that adapter lands.
++ hub reporting, 26 tests.
+
+`glas_harness/reins/rein_openweights.py` now implements the `Rein` ABC
+by shelling out to `rein-openweights run --task-file ... --no-hub
+[--model ...]`, mirroring `reins/rein_aharness.py` exactly (both now
+share `reins/_shared.py` for `git_head`/`write_task_file` — the
+duplication was real, so it got factored out). `registry/reins/
+rein-openweights.yaml` flipped to `status: implemented`. 8 new tests,
+all mocked.
 
 ```task
 id: GLAS-WP-0001-T05
-status: progress
+status: done
 priority: high
 state_hub_task_id: "84fa62ae-3b34-42fd-a263-f65c35e87586"
 ```