diff --git a/src/spotoptim/optimizer/steady_state.py b/src/spotoptim/optimizer/steady_state.py
index f113195..d7c60a7 100644
--- a/src/spotoptim/optimizer/steady_state.py
+++ b/src/spotoptim/optimizer/steady_state.py
@@ -322,6 +322,23 @@ def _batch_ready() -> bool:
                                 optimizer._update_storage_steady(xi, yi)
                                 optimizer.n_iter_ += 1
 
+                            # TensorBoard: this result loop runs only in the
+                            # parent main thread (workers carry tb_writer=None,
+                            # search threads never touch the writer), so the
+                            # single SummaryWriter needs no lock. update_stats()
+                            # refreshes ``counter`` (the TB step) which the
+                            # steady-state loop otherwise never advances; it is
+                            # kept inside the guard so the no-TB path stays
+                            # byte-identical. Mirrors the sequential per-eval
+                            # logging in the main optimize loop.
+                            if optimizer.tb_writer is not None:
+                                optimizer.update_stats()
+                                for xi, yi in zip(X_done, y_done):
+                                    optimizer._write_tensorboard_hparams(
+                                        np.asarray(xi, dtype=float), float(yi)
+                                    )
+                                optimizer._write_tensorboard_scalars()
+
                             if optimizer.verbose:
                                 if optimizer.max_time != np.inf:
                                     prog_val = (
diff --git a/tests/test_tensorboard_parallel.py b/tests/test_tensorboard_parallel.py
index d60faf4..3ba372a 100644
--- a/tests/test_tensorboard_parallel.py
+++ b/tests/test_tensorboard_parallel.py
@@ -2,8 +2,12 @@
 #
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
+import os
+
 import numpy as np
 import pytest
+from tensorboard.backend.event_processing.event_accumulator import EventAccumulator
+
 from spotoptim import SpotOptim
 
 
@@ -16,6 +20,22 @@ def dummy_func(X):
     return np.sum(X**2, axis=1)
 
 
+def _count_scalar_steps(logdir, tag="success_rate"):
+    """Return the number of distinct steps logged for a scalar tag.
+
+    add_scalar events land in the run root; add_hparams events land in
+    per-call subdirectories, so every event file under ``logdir`` is read.
+    """
+    steps = set()
+    for root, _dirs, files in os.walk(str(logdir)):
+        if any(f.startswith("events.out.tfevents") for f in files):
+            acc = EventAccumulator(root)
+            acc.Reload()
+            if tag in acc.Tags().get("scalars", []):
+                steps.update(e.step for e in acc.Scalars(tag))
+    return len(steps)
+
+
 def test_tensorboard_enabled_in_parallel(capsys):
     """Test that TensorBoard is ENABLED when n_jobs > 1 (steady-state)."""
     opt = SpotOptim(
@@ -57,6 +77,53 @@ def test_tensorboard_enabled_in_parallel(capsys):
     opt.optimize()
 
 
+def test_parallel_logs_infill_evals(tmp_path):
+    """Steady-state parallel runs log scalars beyond the initial design.
+
+    Regression test for the gap where workers carry ``tb_writer=None`` and
+    the parent result loop never wrote per-eval scalars, so parallel runs
+    logged only the initial design (one step).
+    """
+    n_initial, max_iter = 4, 12
+    path = str(tmp_path / "tb_parallel")
+    opt = SpotOptim(
+        fun=dummy_func,
+        bounds=[(-5, 5)],
+        n_initial=n_initial,
+        max_iter=max_iter,
+        n_jobs=2,
+        tensorboard_log=True,
+        tensorboard_path=path,
+        seed=0,
+        verbose=False,
+    )
+    opt.optimize()
+
+    assert len(opt.y_) > n_initial, "expected infill evaluations beyond n_initial"
+    # Before the fix, success_rate appeared at a single step (initial design
+    # only). With per-eval parent-side logging it advances with each batch.
+    assert _count_scalar_steps(path, "success_rate") > 1
+
+
+def test_parallel_no_tensorboard_regression(tmp_path):
+    """tensorboard_log=False parallel run is unaffected: no writer, no runs dir."""
+    opt = SpotOptim(
+        fun=dummy_func,
+        bounds=[(-5, 5)],
+        n_initial=4,
+        max_iter=10,
+        n_jobs=2,
+        tensorboard_log=False,
+        seed=0,
+        verbose=False,
+    )
+    res = opt.optimize()
+
+    assert opt.tb_writer is None
+    assert res.success is True
+    assert not (tmp_path / "runs").exists()
+
+
 def test_tensorboard_enabled_in_sequential():
     """Test that TensorBoard IS enabled when n_jobs = 1."""
     opt = SpotOptim(