diff --git a/autogalaxy/config/latent.yaml b/autogalaxy/config/latent.yaml
index 149b6494..fd4f783f 100644
--- a/autogalaxy/config/latent.yaml
+++ b/autogalaxy/config/latent.yaml
@@ -8,13 +8,22 @@
 # Workspaces should mirror this file in their own `config/latent.yaml` to
 # override defaults locally (workspace values shadow library values).
 
-# `total_galaxy_0_flux_mujy` — total integrated flux of the first galaxy in
-# the fit (i.e. `fit.galaxies[0]`), converted from the fit's linear flux
-# units to microjanskies via `magzero` passed through Analysis kwargs.
+# `total_galaxy_0_flux` — total integrated flux of the first galaxy
+# (`fit.galaxies[0]`) in the raw image units the fit was performed in.
 # Returns NaN when galaxy 0 has no light profile.
 #
-# Default `false` because computing this latent requires the user to pass
-# `magzero=<value>` to `AnalysisImaging(...)` — if the value is missing the
-# computation raises loudly (no silent NaN). Users who want this latent
-# should enable it here AND pass `magzero` via Analysis kwargs.
+# Requires no instrument inputs — default `true`. See the workspace flux
+# guide (`scripts/guides/units/flux.py`) for how to convert this to a
+# microjansky flux using a user-supplied `magzero`.
+total_galaxy_0_flux: true
+
+# `total_galaxy_0_flux_mujy` — the same total flux converted to
+# microjanskies via `magzero` passed through Analysis kwargs.
+#
+# Default `false` because the conversion needs a per-instrument zero-point
+# that the user must supply (`AnalysisImaging(..., magzero=<value>)`). When
+# enabled without a `magzero`, the latent returns NaN and emits a single
+# warning per process — it does not raise. Workspaces with a known
+# zero-point (e.g. the Euclid pipeline) override this to `true` and pass
+# `magzero` explicitly.
 total_galaxy_0_flux_mujy: false
diff --git a/autogalaxy/imaging/model/latent.py b/autogalaxy/imaging/model/latent.py
index 9f7e53c2..5a3e40e7 100644
--- a/autogalaxy/imaging/model/latent.py
+++ b/autogalaxy/imaging/model/latent.py
@@ -20,6 +20,33 @@
 
 logger = logging.getLogger(__name__)
 
+# Latent names that have already emitted a "magzero missing" warning in this
+# process. Used by ``_maybe_magzero_warn`` to deduplicate the message across
+# the many fit evaluations a single search performs.
+_MAGZERO_WARNED: set = set()
+
+
+def _maybe_magzero_warn(magzero, name) -> bool:
+    """
+    Return True when ``magzero`` is missing (and emit a one-time-per-process
+    warning for ``name``); False otherwise.
+
+    Callers that get True must early-return ``xp.nan`` — the µJy conversion
+    is meaningless without a zero-point, but a search-killing raise here
+    would discard otherwise-converged fits.
+    """
+    if magzero is None:
+        if name not in _MAGZERO_WARNED:
+            logger.warning(
+                "magzero not set on Analysis; '%s' latent will be NaN. "
+                "Pass magzero=<value> to AnalysisImaging to enable it, "
+                "or disable in config/latent.yaml to silence this warning.",
+                name,
+            )
+            _MAGZERO_WARNED.add(name)
+        return True
+    return False
+
 
 def ab_mag_via_flux_from(flux, magzero, xp=np):
     """
@@ -48,22 +75,43 @@ def flux_mujy_via_ab_mag_from(ab_mag, xp=np):
     return 10 ** ((23.9 - ab_mag) / 2.5)
 
 
+def total_galaxy_0_flux(fit, magzero=None, xp=np):
+    """
+    Total integrated flux of the first galaxy in the fit, in the raw image
+    units the fit was performed in (the sum of the model image pixels).
+
+    Requires no instrument inputs — ``magzero`` is accepted for uniform
+    dispatcher context but ignored. See ``autolens_workspace`` and
+    ``autogalaxy_workspace`` flux guides for how to convert this to a
+    microjansky flux using a user-supplied ``magzero``.
+
+    Returns NaN when the first galaxy has no light profile (which raises
+    inside ``fit.galaxy_image_dict``).
+    """
+    try:
+        image = fit.galaxy_image_dict[fit.galaxies[0]]
+    except (AttributeError, KeyError, IndexError):
+        return xp.nan
+    return xp.sum(image.array)
+
+
 def total_galaxy_0_flux_mujy(fit, magzero, xp=np):
     """
     Total integrated flux of the first galaxy in the fit, converted to
     microjanskies via the image's magnitude zero-point.
 
-    Returns NaN when the first galaxy has no light profile (which raises
-    AttributeError inside ``fit.galaxy_image_dict``). Raises if ``magzero``
-    is missing — there is no sensible default for a photometric calibration.
+    Returns NaN — with a one-time-per-process warning — when ``magzero``
+    is missing, rather than raising. The µJy conversion is meaningless
+    without a zero-point, but a hard raise during post-fit latent
+    computation would discard the result of an otherwise-converged
+    multi-hour search. Users who want this column populated should pass
+    ``magzero=<value>`` to ``AnalysisImaging`` (Euclid pipeline pattern)
+    or use :func:`total_galaxy_0_flux` and convert in post.
+
+    Also returns NaN when the first galaxy has no light profile.
     """
-    if magzero is None:
-        raise ValueError(
-            "magzero must be passed to AnalysisImaging via kwargs to compute "
-            "the 'total_galaxy_0_flux_mujy' latent. Disable it in "
-            "config/latent.yaml or pass magzero=<value> when constructing "
-            "the Analysis."
-        )
+    if _maybe_magzero_warn(magzero, "total_galaxy_0_flux_mujy"):
+        return xp.nan
 
     try:
         image = fit.galaxy_image_dict[fit.galaxies[0]]
@@ -76,6 +124,7 @@ def total_galaxy_0_flux_mujy(fit, magzero, xp=np):
 
 
 LATENT_FUNCTIONS: Dict[str, Callable] = {
+    "total_galaxy_0_flux": total_galaxy_0_flux,
     "total_galaxy_0_flux_mujy": total_galaxy_0_flux_mujy,
 }
 
diff --git a/test_autogalaxy/config/latent.yaml b/test_autogalaxy/config/latent.yaml
index db77b885..eb0eaaad 100644
--- a/test_autogalaxy/config/latent.yaml
+++ b/test_autogalaxy/config/latent.yaml
@@ -1,4 +1,8 @@
 # Test config mirror of `autogalaxy/config/latent.yaml`. Pushed by the
 # autouse `set_config_path` fixture in `test_autogalaxy/conftest.py`, which
 # shadows the library defaults during the test suite.
+#
+# The µJy key is `true` here (vs `false` in the library default) so the
+# test suite exercises both the raw-flux and magzero-converted paths.
+total_galaxy_0_flux: true
 total_galaxy_0_flux_mujy: true
diff --git a/test_autogalaxy/imaging/model/test_latent.py b/test_autogalaxy/imaging/model/test_latent.py
index f585e9a5..94d3badb 100644
--- a/test_autogalaxy/imaging/model/test_latent.py
+++ b/test_autogalaxy/imaging/model/test_latent.py
@@ -7,11 +7,13 @@
 
 import autofit as af
 import autogalaxy as ag
+from autogalaxy.imaging.model import latent as _latent_module
 from autogalaxy.imaging.model.latent import (
     LATENT_FUNCTIONS,
     ab_mag_via_flux_from,
     flux_mujy_via_ab_mag_from,
     latent_keys_enabled,
+    total_galaxy_0_flux,
     total_galaxy_0_flux_mujy,
 )
 
@@ -55,29 +57,76 @@ def test_total_galaxy_0_flux_mujy_returns_nan_when_no_light_profile():
     assert np.isnan(result)
 
 
-def test_total_galaxy_0_flux_mujy_missing_magzero_raises():
+def test_total_galaxy_0_flux_mujy_missing_magzero_returns_nan_and_warns(caplog):
+    _latent_module._MAGZERO_WARNED.discard("total_galaxy_0_flux_mujy")
+    caplog.set_level(logging.WARNING)
+
+    image = SimpleNamespace(array=np.array([1.0, 2.0, 3.0]))
+    galaxy = object()
+    fit = SimpleNamespace(galaxies=[galaxy], galaxy_image_dict={galaxy: image})
+
+    result = total_galaxy_0_flux_mujy(fit=fit, magzero=None)
+
+    assert np.isnan(result)
+    assert any(
+        "magzero" in rec.message and "total_galaxy_0_flux_mujy" in rec.message
+        for rec in caplog.records
+    )
+
+
+def test_total_galaxy_0_flux_against_known_image():
+    image = SimpleNamespace(array=np.array([1.0, 2.0, 3.0, 4.0]))
+    galaxy = object()
+    fit = SimpleNamespace(galaxies=[galaxy], galaxy_image_dict={galaxy: image})
+
+    # Raw sum — no AB-mag conversion. `magzero` is accepted but ignored.
+    assert total_galaxy_0_flux(fit=fit, magzero=None) == pytest.approx(10.0)
+    assert total_galaxy_0_flux(fit=fit, magzero=25.0) == pytest.approx(10.0)
+
+
+def test_total_galaxy_0_flux_returns_nan_when_no_light_profile():
     fit = MagicMock()
+    fit.galaxy_image_dict.__getitem__.side_effect = KeyError("no light")
+    fit.galaxies = [object()]
+
+    assert np.isnan(total_galaxy_0_flux(fit=fit))
+
+
+def test_maybe_magzero_warn_logs_only_once_per_name(caplog):
+    _latent_module._MAGZERO_WARNED.discard("total_galaxy_0_flux_mujy")
+    caplog.set_level(logging.WARNING)
 
-    with pytest.raises(ValueError, match="magzero"):
+    image = SimpleNamespace(array=np.array([1.0]))
+    galaxy = object()
+    fit = SimpleNamespace(galaxies=[galaxy], galaxy_image_dict={galaxy: image})
+
+    for _ in range(3):
         total_galaxy_0_flux_mujy(fit=fit, magzero=None)
 
+    matching = [
+        r for r in caplog.records if "total_galaxy_0_flux_mujy" in r.message
+    ]
+    assert len(matching) == 1
+
 
 def test_latent_keys_enabled_filters_disabled():
-    enabled = latent_keys_enabled(yaml_config={"total_galaxy_0_flux_mujy": False})
+    enabled = latent_keys_enabled(
+        yaml_config={
+            "total_galaxy_0_flux": False,
+            "total_galaxy_0_flux_mujy": False,
+        }
+    )
     assert enabled == []
 
 
 def test_latent_keys_enabled_preserves_yaml_order():
-    # Insert an unknown second key so we can assert ordering across two keys
-    # without depending on a future second registered latent.
     yaml_config = {
         "total_galaxy_0_flux_mujy": True,
-        "future_latent_zzz": True,
+        "total_galaxy_0_flux": True,
     }
     enabled = latent_keys_enabled(yaml_config=yaml_config)
 
-    # Unknown keys drop; the known key stays in its yaml-insertion position.
-    assert enabled == ["total_galaxy_0_flux_mujy"]
+    assert enabled == ["total_galaxy_0_flux_mujy", "total_galaxy_0_flux"]
 
 
 def test_latent_keys_enabled_drops_unknown_with_warning(caplog):
@@ -105,8 +154,9 @@ def test_analysis_imaging_compute_latent_variables_aligns_with_latent_keys(
 
     assert isinstance(values, tuple)
     assert len(values) == len(analysis.LATENT_KEYS)
-    assert analysis.LATENT_KEYS == ["total_galaxy_0_flux_mujy"]
-    assert np.isfinite(values[0])
+    # test_autogalaxy/config/latent.yaml enables both keys, raw flux first.
+    assert analysis.LATENT_KEYS == ["total_galaxy_0_flux", "total_galaxy_0_flux_mujy"]
+    assert all(np.isfinite(v) for v in values)
 
 
 def test_analysis_imaging_compute_latent_variables_raises_when_empty(monkeypatch):
@@ -126,9 +176,9 @@ def test_analysis_imaging_compute_latent_variables_raises_when_empty(monkeypatch
 
 def test_analysis_imaging_latent_keys_property_reads_config():
     # The autouse fixture in test_autogalaxy/conftest.py pushes the test
-    # config dir whose latent.yaml enables total_galaxy_0_flux_mujy.
+    # config dir whose latent.yaml enables both keys.
     dataset = MagicMock()
     analysis = ag.AnalysisImaging(dataset=dataset, use_jax=False)
 
-    assert analysis.LATENT_KEYS == ["total_galaxy_0_flux_mujy"]
+    assert analysis.LATENT_KEYS == ["total_galaxy_0_flux", "total_galaxy_0_flux_mujy"]
     assert set(analysis.LATENT_KEYS).issubset(LATENT_FUNCTIONS.keys())