From 82846655ac32f4d7836d4586d4e4e1036f227a8c Mon Sep 17 00:00:00 2001
From: Robin Linacre <robinlinacre@hotmail.com>
Date: Sun, 15 Feb 2026 13:18:00 +0000
Subject: [PATCH 01/20] filtered neighbours gets persisted

---
 splink/internals/spark/database_api.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/splink/internals/spark/database_api.py b/splink/internals/spark/database_api.py
index 7a55bdc04e..6dbbc20ac7 100644
--- a/splink/internals/spark/database_api.py
+++ b/splink/internals/spark/database_api.py
@@ -299,6 +299,7 @@ def _break_lineage_and_repartition(self, spark_df, templated_name, physical_name
             r"__splink__clusters_at_all_thresholds",
             r"__splink__clustering_output_final",
             r"__splink__stable_nodes_at_new_threshold",
+            r"__splink__filtered_neighbours.*",
         ]
 
         if re.fullmatch(r"|".join(regex_to_persist), templated_name):

From f71f382fd5c76048d5ae2ccccf5f26d849639321 Mon Sep 17 00:00:00 2001
From: Robin Linacre <robinlinacre@hotmail.com>
Date: Sun, 15 Feb 2026 13:32:57 +0000
Subject: [PATCH 02/20] 4.0.14 release and changelog

---
 CHANGELOG.md       | 7 ++++++-
 pyproject.toml     | 2 +-
 splink/__init__.py | 2 +-
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 44fa10003a..c5136fbc0c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,7 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## Unreleased
+## [4.0.14] - 2026-02-12
+
+### Changed
+
+* Two dataset link only exploding blocking rule optimisation by @RobinL in https://github.com/moj-analytical-services/splink/pull/2931
+* Filtered neighbours gets persisted by @RobinL in https://github.com/moj-analytical-services/splink/pull/2933
 
 ## [4.0.13] - 2026-02-12
 
diff --git a/pyproject.toml b/pyproject.toml
index 404cf95217..7c319b4ed9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "splink"
-version = "4.0.13"
+version = "4.0.14"
 description = "Fast probabilistic data linkage at scale"
 authors = [
     { name = "Robin Linacre", email = "robinlinacre@hotmail.com" },
diff --git a/splink/__init__.py b/splink/__init__.py
index 55f661ea94..56088d76f0 100644
--- a/splink/__init__.py
+++ b/splink/__init__.py
@@ -56,7 +56,7 @@ def __getattr__(name):
     raise AttributeError(f"module 'splink' has no attribute '{name}'") from None
 
 
-__version__ = "4.0.13"
+__version__ = "4.0.14"
 
 
 __all__ = [

From 8dc6c93dbc5f63deee34a11baead9877bada6f99 Mon Sep 17 00:00:00 2001
From: Robin Linacre <robinlinacre@hotmail.com>
Date: Mon, 16 Feb 2026 07:44:36 +0000
Subject: [PATCH 03/20] faster join to blocked pairs

---
 splink/internals/comparison_vector_values.py | 22 +++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/splink/internals/comparison_vector_values.py b/splink/internals/comparison_vector_values.py
index ae6341543c..6f6f09ef10 100644
--- a/splink/internals/comparison_vector_values.py
+++ b/splink/internals/comparison_vector_values.py
@@ -4,7 +4,9 @@
 from typing import List, Optional
 
 from splink.internals.input_column import InputColumn
-from splink.internals.unique_id_concat import _composite_unique_id_from_nodes_sql
+from splink.internals.unique_id_concat import (
+    _composite_unique_id_from_nodes_sql,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -62,18 +64,28 @@ def compute_comparison_vector_values_from_id_pairs_sqls(
     uid_l_expr = _composite_unique_id_from_nodes_sql(unique_id_columns, "l")
     uid_r_expr = _composite_unique_id_from_nodes_sql(unique_id_columns, "r")
 
+    # The where condition shouldn't really do anything because
+    # it's already covered by the inner join.
+    # However, Where there are large numbers of unmatched records, the DuckDB query
+    # planner can struggle with the double inner join below.  It should
+    # push the filters down to the input tables, but it doesn't always do this.
+    # This forces it.
+
     # The first table selects the required columns from the input tables
     # and alises them as `col_l`, `col_r` etc
     # using the __splink__blocked_id_pairs as an associated (junction) table
-
     # That is, it does the join, but doesn't compute the comparison vectors
-    sql = sql = f"""
+    sql = f"""
     select {select_cols_expr}, b.match_key
-    from {input_tablename_l} as l
-    inner join __splink__blocked_id_pairs as b
+    from __splink__blocked_id_pairs as b
+    inner join {input_tablename_l} as l
     on {uid_l_expr} = b.join_key_l
     inner join {input_tablename_r} as r
     on {uid_r_expr} = b.join_key_r
+    where
+    {uid_l_expr} in (select join_key_l from __splink__blocked_id_pairs)
+    or
+    {uid_r_expr} in (select join_key_r from __splink__blocked_id_pairs)
     """
 
     sqls.append({"sql": sql, "output_table_name": "blocked_with_cols"})

From 997eddd4c2e2c74ec2a784b49fa6e968e025ca19 Mon Sep 17 00:00:00 2001
From: Robin Linacre <robinlinacre@hotmail.com>
Date: Mon, 16 Feb 2026 08:40:58 +0000
Subject: [PATCH 04/20] faster join to blocked pairs

---
 splink/internals/comparison_vector_values.py | 33 +++++++++++++-------
 1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/splink/internals/comparison_vector_values.py b/splink/internals/comparison_vector_values.py
index 6f6f09ef10..c4befd3528 100644
--- a/splink/internals/comparison_vector_values.py
+++ b/splink/internals/comparison_vector_values.py
@@ -6,6 +6,7 @@
 from splink.internals.input_column import InputColumn
 from splink.internals.unique_id_concat import (
     _composite_unique_id_from_nodes_sql,
+    _composite_unique_id_from_edges_sql,
 )
 
 logger = logging.getLogger(__name__)
@@ -61,15 +62,29 @@ def compute_comparison_vector_values_from_id_pairs_sqls(
 
     select_cols_expr = ", \n".join(columns_to_select_for_blocking)
 
-    uid_l_expr = _composite_unique_id_from_nodes_sql(unique_id_columns, "l")
-    uid_r_expr = _composite_unique_id_from_nodes_sql(unique_id_columns, "r")
-
-    # The where condition shouldn't really do anything because
-    # it's already covered by the inner join.
-    # However, Where there are large numbers of unmatched records, the DuckDB query
-    # planner can struggle with the double inner join below.  It should
+    # Where there are large numbers of unmatched records, the DuckDB query planner
+    # Can struggle with the double inner join below.  It should
     # push the filters down to the input tables, but it doesn't always do this.
     # This forces it.
+    if input_tablename_l == input_tablename_r:
+        uid_expr = _composite_unique_id_from_nodes_sql(unique_id_columns)
+        sql = f"""
+        select *
+        from {input_tablename_l}
+        where
+        {uid_expr} in (select join_key_l from __splink__blocked_id_pairs)
+        or
+        {uid_expr} in (select join_key_r from __splink__blocked_id_pairs)
+        """
+
+        sqls.append(
+            {"sql": sql, "output_table_name": "__splink__df_concat_with_tf_filtered"}
+        )
+        input_tablename_l = "__splink__df_concat_with_tf_filtered"
+        input_tablename_r = "__splink__df_concat_with_tf_filtered"
+
+    uid_l_expr = _composite_unique_id_from_nodes_sql(unique_id_columns, "l")
+    uid_r_expr = _composite_unique_id_from_nodes_sql(unique_id_columns, "r")
 
     # The first table selects the required columns from the input tables
     # and alises them as `col_l`, `col_r` etc
@@ -82,10 +97,6 @@ def compute_comparison_vector_values_from_id_pairs_sqls(
     on {uid_l_expr} = b.join_key_l
     inner join {input_tablename_r} as r
     on {uid_r_expr} = b.join_key_r
-    where
-    {uid_l_expr} in (select join_key_l from __splink__blocked_id_pairs)
-    or
-    {uid_r_expr} in (select join_key_r from __splink__blocked_id_pairs)
     """
 
     sqls.append({"sql": sql, "output_table_name": "blocked_with_cols"})

From 853c0f25fef63e92c1e18f6282b6c1712b3f8b79 Mon Sep 17 00:00:00 2001
From: Robin Linacre <robinlinacre@hotmail.com>
Date: Mon, 16 Feb 2026 08:42:19 +0000
Subject: [PATCH 05/20] clean up

---
 splink/internals/comparison_vector_values.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/splink/internals/comparison_vector_values.py b/splink/internals/comparison_vector_values.py
index c4befd3528..7149646c7b 100644
--- a/splink/internals/comparison_vector_values.py
+++ b/splink/internals/comparison_vector_values.py
@@ -6,7 +6,6 @@
 from splink.internals.input_column import InputColumn
 from splink.internals.unique_id_concat import (
     _composite_unique_id_from_nodes_sql,
-    _composite_unique_id_from_edges_sql,
 )
 
 logger = logging.getLogger(__name__)

From 53021d059020793770fd95b4547821a4d997e270 Mon Sep 17 00:00:00 2001
From: Robin Linacre <robinlinacre@hotmail.com>
Date: Tue, 17 Feb 2026 18:01:40 +0000
Subject: [PATCH 06/20] pass correct args

---
 splink/internals/comparison_vector_values.py    | 17 ++++++++++++++---
 splink/internals/linker_components/inference.py |  4 ++++
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/splink/internals/comparison_vector_values.py b/splink/internals/comparison_vector_values.py
index 7149646c7b..97b86bebf1 100644
--- a/splink/internals/comparison_vector_values.py
+++ b/splink/internals/comparison_vector_values.py
@@ -45,6 +45,8 @@ def compute_comparison_vector_values_from_id_pairs_sqls(
     source_dataset_input_column: Optional[InputColumn],
     unique_id_input_column: InputColumn,
     include_clerical_match_score: bool = False,
+    link_type: Optional[str] = None,
+    sql_dialect_str: Optional[str] = None,
 ) -> list[dict[str, str]]:
     """Compute the comparison vectors from __splink__blocked_id_pairs, the
     materialised dataframe of blocked pairwise record comparisons.
@@ -62,10 +64,19 @@ def compute_comparison_vector_values_from_id_pairs_sqls(
     select_cols_expr = ", \n".join(columns_to_select_for_blocking)
 
     # Where there are large numbers of unmatched records, the DuckDB query planner
-    # Can struggle with the double inner join below.  It should
+    # can struggle with the double inner join below.  It should
     # push the filters down to the input tables, but it doesn't always do this.
-    # This forces it.
-    if input_tablename_l == input_tablename_r:
+    # This forces it.  it is only really relevant in the link only case,
+    # where one dataset is much larger than the other
+    # This optimisation is here due to poor performance observed in
+    # the `uk_address_matcher` package
+    # TODO: Once DuckDB 1.5 is released, check this is still needed
+    # ref https://github.com/moj-analytical-services/uk_address_matcher/issues/226
+    if (
+        input_tablename_l == input_tablename_r
+        and link_type == "two_dataset_link_only"
+        and sql_dialect_str == "duckdb"
+    ):
         uid_expr = _composite_unique_id_from_nodes_sql(unique_id_columns)
         sql = f"""
         select *
diff --git a/splink/internals/linker_components/inference.py b/splink/internals/linker_components/inference.py
index 280b074705..e0b92d4e4b 100644
--- a/splink/internals/linker_components/inference.py
+++ b/splink/internals/linker_components/inference.py
@@ -139,6 +139,8 @@ def deterministic_link(self) -> SplinkDataFrame:
             input_tablename_r="__splink__df_concat_with_tf",
             source_dataset_input_column=self._linker._settings_obj.column_info_settings.source_dataset_input_column,
             unique_id_input_column=self._linker._settings_obj.column_info_settings.unique_id_input_column,
+            link_type=link_type,
+            sql_dialect_str=self._linker._sql_dialect_str,
         )
         pipeline.enqueue_list_of_sqls(sqls)
 
@@ -268,6 +270,8 @@ def predict(
             input_tablename_r="__splink__df_concat_with_tf",
             source_dataset_input_column=self._linker._settings_obj.column_info_settings.source_dataset_input_column,
             unique_id_input_column=self._linker._settings_obj.column_info_settings.unique_id_input_column,
+            link_type=link_type,
+            sql_dialect_str=self._linker._sql_dialect_str,
         )
         pipeline.enqueue_list_of_sqls(sqls)
 

From b599a0165423b4dc64ed8be9bfc04cbda828b848 Mon Sep 17 00:00:00 2001
From: Robin Linacre <robinlinacre@hotmail.com>
Date: Tue, 17 Feb 2026 21:04:25 +0000
Subject: [PATCH 07/20] 4_0_15 release

---
 CHANGELOG.md       | 9 +++++++++
 pyproject.toml     | 2 +-
 splink/__init__.py | 2 +-
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c5136fbc0c..b14d9ddca8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,15 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+
+## [4.0.15] - 2026-02-17
+
+### Changed
+
+Faster two_dataset_link_only joins when joining small table to large in duckdb by @RobinL in https://github.com/moj-analytical-services/splink/pull/2936
+
 ## [4.0.14] - 2026-02-12
 
 ### Changed
diff --git a/pyproject.toml b/pyproject.toml
index 7c319b4ed9..5954967a15 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "splink"
-version = "4.0.14"
+version = "4.0.15"
 description = "Fast probabilistic data linkage at scale"
 authors = [
     { name = "Robin Linacre", email = "robinlinacre@hotmail.com" },
diff --git a/splink/__init__.py b/splink/__init__.py
index 56088d76f0..903bd7ee0d 100644
--- a/splink/__init__.py
+++ b/splink/__init__.py
@@ -56,7 +56,7 @@ def __getattr__(name):
     raise AttributeError(f"module 'splink' has no attribute '{name}'") from None
 
 
-__version__ = "4.0.14"
+__version__ = "4.0.15"
 
 
 __all__ = [

From e626bf6f5ad2f66380ed13b1575d33c34f76cc65 Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Tue, 17 Feb 2026 11:04:47 +0000
Subject: [PATCH 08/20] remove orphaned chart

gone since https://github.com/moj-analytical-services/splink/pull/2157
---
 splink/internals/charts.py                    | 14 ----
 .../files/chart_defs/missingness.json         | 80 -------------------
 2 files changed, 94 deletions(-)
 delete mode 100644 splink/internals/files/chart_defs/missingness.json

diff --git a/splink/internals/charts.py b/splink/internals/charts.py
index 9f1a4a31fa..d48b1981de 100644
--- a/splink/internals/charts.py
+++ b/splink/internals/charts.py
@@ -349,20 +349,6 @@ def parameter_estimate_comparisons(records, as_dict=False):
     return altair_or_json(chart, as_dict=as_dict)
 
 
-def missingness_chart(records, as_dict=False):
-    chart_path = "missingness.json"
-    chart = load_chart_definition(chart_path)
-
-    chart["data"]["values"] = records
-
-    record_count = records[0]["total_record_count"]
-
-    for c in chart["layer"]:
-        c["title"] = f"Missingness per column out of {record_count:,.0f} records"
-
-    return altair_or_json(chart, as_dict=as_dict)
-
-
 def unlinkables_chart(
     records,
     x_col="match_weight",
diff --git a/splink/internals/files/chart_defs/missingness.json b/splink/internals/files/chart_defs/missingness.json
deleted file mode 100644
index de18f660fb..0000000000
--- a/splink/internals/files/chart_defs/missingness.json
+++ /dev/null
@@ -1,80 +0,0 @@
-{
-  "config": {
-    "view": {
-      "continuousWidth": 400,
-      "continuousHeight": 300
-    },
-    "axis": {
-      "labelFontSize": 11
-    }
-  },
-  "title": "",
-  "layer": [
-    {
-      "mark": "bar",
-      "encoding": {
-        "color": {
-          "type": "quantitative",
-          "field": "null_proportion",
-          "legend": {
-            "format": ".0%",
-            "offset": 30
-          },
-          "scale": {"domain": [0, 1],
-            "range": "heatmap"
-          },
-          "title": "Missingness"
-        },
-        "tooltip": [
-          {
-            "type": "nominal",
-            "field": "column_name",
-            "title": "Column"
-          },
-          {
-            "type": "quantitative",
-            "field": "null_count",
-            "format": ",.0f",
-            "title": "Count of nulls"
-          },
-          {
-            "type": "quantitative",
-            "field": "null_proportion",
-            "format": ".2%",
-            "title": "Percentage of nulls"
-          },
-          {
-            "type": "quantitative",
-            "field": "total_record_count",
-            "format": ",.0f",
-            "title": "Total record count"
-          }
-        ],
-        "x": {
-          "type": "quantitative",
-          "scale": {"domain": [0, 1]},
-          "axis": {
-            "labelAlign": "center",
-            "format": "%",
-            "title": "Percentage of nulls"
-          },
-          "field": "null_proportion"
-        },
-        "y": {
-          "type": "nominal",
-          "axis": {
-            "title": ""
-          },
-          "field": "column_name",
-          "sort": "-x"
-        }
-      },
-      "title": ""
-    }
-  ],
-  "data": {
-    "values": "",
-    "name": "data-0e7bce5a1d2f132e282789d6ef7780fe"
-  },
-  "$schema": "https://vega.github.io/schema/vega-lite/v5.9.3.json"
-}

From bbf2568756850786dca4d943ace62813b3db9136 Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Tue, 17 Feb 2026 13:08:54 +0000
Subject: [PATCH 09/20] cl detailed record as dataclass

---
 splink/internals/comparison.py       |  4 +-
 splink/internals/comparison_level.py | 85 +++++++++++++++++-----------
 splink/internals/waterfall_chart.py  |  6 +-
 3 files changed, 58 insertions(+), 37 deletions(-)

diff --git a/splink/internals/comparison.py b/splink/internals/comparison.py
index c7e69492d6..0f8d134937 100644
--- a/splink/internals/comparison.py
+++ b/splink/internals/comparison.py
@@ -367,7 +367,9 @@ def _as_detailed_records(self) -> list[dict[str, Any]]:
             record["comparison_name"] = self.output_column_name
             record = {
                 **record,
-                **cl._as_detailed_record(self._num_levels, self.comparison_levels),
+                **cl._as_detailed_record(
+                    self._num_levels, self.comparison_levels
+                ).as_dict(),
             }
             records.append(record)
         return records
diff --git a/splink/internals/comparison_level.py b/splink/internals/comparison_level.py
index 61aa669711..026e135ff8 100644
--- a/splink/internals/comparison_level.py
+++ b/splink/internals/comparison_level.py
@@ -4,6 +4,7 @@
 import math
 import re
 from copy import copy
+from dataclasses import asdict, dataclass
 from statistics import median
 from textwrap import dedent
 from typing import Any, Optional, Union, cast
@@ -116,6 +117,33 @@ def _default_u_values(num_levels: int) -> list[float]:
     return u_vals
 
 
+@dataclass
+class ComparisonLevelDetailedRecord:
+    sql_condition: str
+    label_for_charts: str
+
+    has_tf_adjustments: bool
+    tf_adjustment_column: str | None
+    tf_adjustment_weight: float
+
+    is_null_level: bool
+
+    m_probability: float | None
+    u_probability: float | None
+    m_probability_description: str | None
+    u_probability_description: str | None
+
+    bayes_factor: float | None
+    log2_bayes_factor: float
+    bayes_factor_description: str
+
+    comparison_vector_value: int
+    max_comparison_vector_value: int
+
+    def as_dict(self):
+        return asdict(self)
+
+
 class ComparisonLevel:
     """Each ComparisonLevel defines a gradation (category) of similarity within a
     `Comparison`.
@@ -735,39 +763,30 @@ def _as_completed_dict(self):
 
     def _as_detailed_record(
         self, comparison_num_levels: int, comparison_levels: list[ComparisonLevel]
-    ) -> dict[str, Any]:
+    ) -> ComparisonLevelDetailedRecord:
         "A detailed representation of this level to describe it in charting outputs"
-        output: dict[str, Any] = {}
-        output["sql_condition"] = self.sql_condition
-        output["label_for_charts"] = self._label_for_charts_no_duplicates(
-            comparison_levels
+        return ComparisonLevelDetailedRecord(
+            sql_condition=self.sql_condition,
+            label_for_charts=self._label_for_charts_no_duplicates(comparison_levels),
+            has_tf_adjustments=self._has_tf_adjustments,
+            tf_adjustment_column=(
+                self._tf_adjustment_input_column.input_name
+                if self._has_tf_adjustments
+                else None
+            ),
+            tf_adjustment_weight=self._tf_adjustment_weight,
+            is_null_level=self.is_null_level,
+            m_probability=self.m_probability if not self.is_null_level else None,
+            u_probability=self.u_probability if not self.is_null_level else None,
+            m_probability_description=self._m_probability_description,
+            u_probability_description=self._u_probability_description,
+            bayes_factor=self._bayes_factor,
+            log2_bayes_factor=self._log2_bayes_factor,
+            bayes_factor_description=self._bayes_factor_description,
+            comparison_vector_value=self.comparison_vector_value,
+            max_comparison_vector_value=comparison_num_levels - 1,
         )
 
-        if not self._is_null_level:
-            output["m_probability"] = self.m_probability
-            output["u_probability"] = self.u_probability
-
-            output["m_probability_description"] = self._m_probability_description
-            output["u_probability_description"] = self._u_probability_description
-
-        output["has_tf_adjustments"] = self._has_tf_adjustments
-        if self._has_tf_adjustments:
-            output["tf_adjustment_column"] = self._tf_adjustment_input_column.input_name
-        else:
-            output["tf_adjustment_column"] = None
-        output["tf_adjustment_weight"] = self._tf_adjustment_weight
-
-        output["is_null_level"] = self.is_null_level
-        output["bayes_factor"] = self._bayes_factor
-        output["log2_bayes_factor"] = self._log2_bayes_factor
-        output["comparison_vector_value"] = self.comparison_vector_value
-        output["max_comparison_vector_value"] = comparison_num_levels - 1
-        output["bayes_factor_description"] = self._bayes_factor_description
-        output["m_probability_description"] = self._m_probability_description
-        output["u_probability_description"] = self._u_probability_description
-
-        return output
-
     def _parameter_estimates_as_records(
         self, comparison_num_levels: int, comparison_levels: list[ComparisonLevel]
     ) -> list[dict[str, Any]]:
@@ -786,9 +805,9 @@ def _parameter_estimates_as_records(
             else:
                 record["estimated_probability_as_log_odds"] = None
 
-            record["sql_condition"] = cl_record["sql_condition"]
-            record["comparison_level_label"] = cl_record["label_for_charts"]
-            record["comparison_vector_value"] = cl_record["comparison_vector_value"]
+            record["sql_condition"] = cl_record.sql_condition
+            record["comparison_level_label"] = cl_record.label_for_charts
+            record["comparison_vector_value"] = cl_record.comparison_vector_value
             output_records.append(record)
 
         return output_records
diff --git a/splink/internals/waterfall_chart.py b/splink/internals/waterfall_chart.py
index a8a080957b..07ef8b3992 100644
--- a/splink/internals/waterfall_chart.py
+++ b/splink/internals/waterfall_chart.py
@@ -57,9 +57,9 @@ def _comparison_records(
     cl = c._get_comparison_level_by_comparison_vector_value(cv_value)
     waterfall_record = {
         field: value
-        for field, value in cl._as_detailed_record(
-            c._num_levels, c.comparison_levels
-        ).items()
+        for field, value in cl._as_detailed_record(c._num_levels, c.comparison_levels)
+        .as_dict()
+        .items()
         if field
         in [
             "label_for_charts",

From 31c2d8c8cd7b46aa0228b0bc1d6ad9157d3136a0 Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Tue, 17 Feb 2026 13:18:59 +0000
Subject: [PATCH 10/20] comparison name in cl detailed rec

---
 splink/internals/comparison.py       | 18 ++++++++----------
 splink/internals/comparison_level.py |  1 +
 2 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/splink/internals/comparison.py b/splink/internals/comparison.py
index 0f8d134937..95816ca2db 100644
--- a/splink/internals/comparison.py
+++ b/splink/internals/comparison.py
@@ -10,7 +10,11 @@
     join_list_with_commas_final_and,
 )
 
-from .comparison_level import ComparisonLevel, _default_m_values, _default_u_values
+from .comparison_level import (
+    ComparisonLevel,
+    _default_m_values,
+    _default_u_values,
+)
 
 # https://stackoverflow.com/questions/39740632/python-type-hinting-without-cyclic-imports
 if TYPE_CHECKING:
@@ -363,15 +367,9 @@ def _is_trained(self):
     def _as_detailed_records(self) -> list[dict[str, Any]]:
         records = []
         for cl in self.comparison_levels:
-            record = {}
-            record["comparison_name"] = self.output_column_name
-            record = {
-                **record,
-                **cl._as_detailed_record(
-                    self._num_levels, self.comparison_levels
-                ).as_dict(),
-            }
-            records.append(record)
+            record = cl._as_detailed_record(self._num_levels, self.comparison_levels)
+            record.comparison_name = self.output_column_name
+            records.append(record.as_dict())
         return records
 
     @property
diff --git a/splink/internals/comparison_level.py b/splink/internals/comparison_level.py
index 026e135ff8..583268518f 100644
--- a/splink/internals/comparison_level.py
+++ b/splink/internals/comparison_level.py
@@ -139,6 +139,7 @@ class ComparisonLevelDetailedRecord:
 
     comparison_vector_value: int
     max_comparison_vector_value: int
+    comparison_name: str | None = None
 
     def as_dict(self):
         return asdict(self)

From e3205ce0558f5660a4421bc40ce42a6ef6787696 Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Tue, 17 Feb 2026 13:30:33 +0000
Subject: [PATCH 11/20] detailed record dataclass in comparison

---
 splink/internals/comparison.py       | 7 ++++---
 splink/internals/settings.py         | 2 +-
 splink/internals/term_frequencies.py | 4 +++-
 3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/splink/internals/comparison.py b/splink/internals/comparison.py
index 95816ca2db..b8988a9934 100644
--- a/splink/internals/comparison.py
+++ b/splink/internals/comparison.py
@@ -12,6 +12,7 @@
 
 from .comparison_level import (
     ComparisonLevel,
+    ComparisonLevelDetailedRecord,
     _default_m_values,
     _default_u_values,
 )
@@ -364,12 +365,12 @@ def _is_trained(self):
         return self._all_m_are_trained and self._all_u_are_trained
 
     @property
-    def _as_detailed_records(self) -> list[dict[str, Any]]:
+    def _as_detailed_records(self) -> list[ComparisonLevelDetailedRecord]:
         records = []
         for cl in self.comparison_levels:
             record = cl._as_detailed_record(self._num_levels, self.comparison_levels)
             record.comparison_name = self.output_column_name
-            records.append(record.as_dict())
+            records.append(record)
         return records
 
     @property
@@ -466,5 +467,5 @@ def match_weights_chart(self, as_dict=False):
         """Display a chart of comparison levels of the comparison"""
         from splink.internals.charts import comparison_match_weights_chart
 
-        records = self._as_detailed_records
+        records = list(map(lambda rec: rec.as_dict(), self._as_detailed_records))
         return comparison_match_weights_chart(records, as_dict=as_dict)
diff --git a/splink/internals/settings.py b/splink/internals/settings.py
index 9a4adea43b..0a5fcde4eb 100644
--- a/splink/internals/settings.py
+++ b/splink/internals/settings.py
@@ -113,7 +113,7 @@ def parameters_as_detailed_records(self):
         output = []
         rr_match = self.probability_two_random_records_match
         for i, cc in enumerate(self.comparisons):
-            records = cc._as_detailed_records
+            records = list(map(lambda rec: rec.as_dict(), cc._as_detailed_records))
             for r in records:
                 r["probability_two_random_records_match"] = rr_match
                 r["comparison_sort_order"] = i
diff --git a/splink/internals/term_frequencies.py b/splink/internals/term_frequencies.py
index da12b12699..85034f6474 100644
--- a/splink/internals/term_frequencies.py
+++ b/splink/internals/term_frequencies.py
@@ -239,7 +239,9 @@ def tf_adjustment_chart(
 
     # Data for chart
     comparison = linker._settings_obj._get_comparison_by_output_column_name(col)
-    comparison_records = comparison._as_detailed_records
+    comparison_records = list(
+        map(lambda rec: rec.as_dict(), comparison._as_detailed_records)
+    )
 
     keys_to_retain = [
         "comparison_vector_value",

From 7eb4d05221c3495d487f997c6f46ee87c09e731e Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Tue, 17 Feb 2026 14:47:20 +0000
Subject: [PATCH 12/20] specialised detailed record for settings

---
 splink/internals/comparison_level.py |  6 +--
 splink/internals/settings.py         | 79 +++++++++++++++++++---------
 2 files changed, 56 insertions(+), 29 deletions(-)

diff --git a/splink/internals/comparison_level.py b/splink/internals/comparison_level.py
index 583268518f..85dcb0208c 100644
--- a/splink/internals/comparison_level.py
+++ b/splink/internals/comparison_level.py
@@ -117,14 +117,14 @@ def _default_u_values(num_levels: int) -> list[float]:
     return u_vals
 
 
-@dataclass
+@dataclass(kw_only=True)
 class ComparisonLevelDetailedRecord:
-    sql_condition: str
+    sql_condition: str | None
     label_for_charts: str
 
     has_tf_adjustments: bool
     tf_adjustment_column: str | None
-    tf_adjustment_weight: float
+    tf_adjustment_weight: float | None
 
     is_null_level: bool
 
diff --git a/splink/internals/settings.py b/splink/internals/settings.py
index 0a5fcde4eb..2d417e3f7c 100644
--- a/splink/internals/settings.py
+++ b/splink/internals/settings.py
@@ -8,7 +8,10 @@
 from splink.internals.blocking import BlockingRule
 from splink.internals.charts import m_u_parameters_chart, match_weights_chart
 from splink.internals.comparison import Comparison
-from splink.internals.comparison_level import ComparisonLevel
+from splink.internals.comparison_level import (
+    ComparisonLevel,
+    ComparisonLevelDetailedRecord,
+)
 from splink.internals.dialects import SplinkDialect
 from splink.internals.input_column import InputColumn
 from splink.internals.misc import (
@@ -27,6 +30,26 @@ class ComparisonAndLevelDict(TypedDict):
     comparison: Comparison
 
 
+@dataclass(kw_only=True)
+class ModelParameterDetailedRecord(ComparisonLevelDetailedRecord):
+    probability_two_random_records_match: float
+    comparison_sort_order: int
+
+    @classmethod
+    def from_cl_detailed_record(
+        cls,
+        cl_rec: ComparisonLevelDetailedRecord,
+        *,
+        probability_two_random_records_match: float,
+        comparison_sort_order: int,
+    ) -> ModelParameterDetailedRecord:
+        return cls(
+            **asdict(cl_rec),
+            probability_two_random_records_match=probability_two_random_records_match,
+            comparison_sort_order=comparison_sort_order,
+        )
+
+
 @dataclass(frozen=True)
 class ColumnInfoSettings:
     match_weight_column_prefix: str
@@ -109,14 +132,18 @@ def copy(self):
         return deepcopy(self)
 
     @property
-    def parameters_as_detailed_records(self):
+    def parameters_as_detailed_records(self) -> list[ModelParameterDetailedRecord]:
         output = []
         rr_match = self.probability_two_random_records_match
         for i, cc in enumerate(self.comparisons):
-            records = list(map(lambda rec: rec.as_dict(), cc._as_detailed_records))
-            for r in records:
-                r["probability_two_random_records_match"] = rr_match
-                r["comparison_sort_order"] = i
+            records = [
+                ModelParameterDetailedRecord.from_cl_detailed_record(
+                    r,
+                    probability_two_random_records_match=rr_match,
+                    comparison_sort_order=i,
+                )
+                for r in cc._as_detailed_records
+            ]
             output.extend(records)
 
         prior_description = (
@@ -128,26 +155,26 @@ def parameters_as_detailed_records(self):
         )
 
         # Finally add a record for probability_two_random_records_match
-        prop_record = {
-            "comparison_name": "probability_two_random_records_match",
-            "sql_condition": None,
-            "label_for_charts": "",
-            "m_probability": None,
-            "u_probability": None,
-            "m_probability_description": None,
-            "u_probability_description": None,
-            "has_tf_adjustments": False,
-            "tf_adjustment_column": None,
-            "tf_adjustment_weight": None,
-            "is_null_level": False,
-            "bayes_factor": prob_to_bayes_factor(rr_match),
-            "log2_bayes_factor": prob_to_match_weight(rr_match),
-            "comparison_vector_value": 0,
-            "max_comparison_vector_value": 0,
-            "bayes_factor_description": prior_description,
-            "probability_two_random_records_match": rr_match,
-            "comparison_sort_order": -1,
-        }
+        prop_record = ModelParameterDetailedRecord(
+            comparison_name="probability_two_random_records_match",
+            sql_condition=None,
+            label_for_charts="",
+            m_probability=None,
+            u_probability=None,
+            m_probability_description=None,
+            u_probability_description=None,
+            has_tf_adjustments=False,
+            tf_adjustment_column=None,
+            tf_adjustment_weight=None,
+            is_null_level=False,
+            bayes_factor=prob_to_bayes_factor(rr_match),
+            log2_bayes_factor=prob_to_match_weight(rr_match),
+            comparison_vector_value=0,
+            max_comparison_vector_value=0,
+            bayes_factor_description=prior_description,
+            probability_two_random_records_match=rr_match,
+            comparison_sort_order=-1,
+        )
         output.insert(0, prop_record)
         return output
 

From f7537d8f71ab40c556d56688b194ec99a5a4c054 Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Tue, 17 Feb 2026 15:26:31 +0000
Subject: [PATCH 13/20] em iteration record subclass

---
 splink/internals/em_training_session.py | 43 +++++++++++++++++++------
 splink/internals/settings.py            |  8 +++--
 2 files changed, 39 insertions(+), 12 deletions(-)

diff --git a/splink/internals/em_training_session.py b/splink/internals/em_training_session.py
index 866d7023ef..cbd25c9c12 100644
--- a/splink/internals/em_training_session.py
+++ b/splink/internals/em_training_session.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import logging
+from dataclasses import asdict, dataclass
 from typing import TYPE_CHECKING, List
 
 from splink.internals.blocking import BlockingRule, block_using_rules_sqls
@@ -22,6 +23,7 @@
 from splink.internals.settings import (
     ComparisonAndLevelDict,
     CoreModelSettings,
+    ModelParameterDetailedRecord,
     Settings,
     TrainingSettings,
 )
@@ -39,6 +41,27 @@
     from splink.internals.splink_dataframe import SplinkDataFrame
 
 
+@dataclass(kw_only=True)
+class ModelParameterIterationDetailedRecord(ModelParameterDetailedRecord):
+    iteration: int
+
+    @classmethod
+    def from_settings_param_detailed_record(
+        cls,
+        cl_rec: ModelParameterDetailedRecord,
+        *,
+        probability_two_random_records_match: float,
+        iteration: int,
+    ) -> ModelParameterIterationDetailedRecord:
+        cl_rec.probability_two_random_records_match = (
+            probability_two_random_records_match
+        )
+        return cls(
+            **asdict(cl_rec),
+            iteration=iteration,
+        )
+
+
 class EMTrainingSession:
     """Manages training models using the Expectation Maximisation algorithm, and
     holds statistics on the evolution of parameter estimates.  Plots diagnostic charts
@@ -320,20 +343,20 @@ def _blocking_adjusted_probability_two_random_records_match(self):
         return adjusted_prop_m
 
     @property
-    def _iteration_history_records(self):
+    def _iteration_history_records(self) -> list[ModelParameterIterationDetailedRecord]:
         output_records = []
 
         for iteration, core_model_settings in enumerate(
             self._core_model_settings_history
         ):
-            records = core_model_settings.parameters_as_detailed_records
-
-            for r in records:
-                r["iteration"] = iteration
-                # TODO: why lambda from current settings, not history?
-                r["probability_two_random_records_match"] = (
-                    self.core_model_settings.probability_two_random_records_match
+            records = [
+                ModelParameterIterationDetailedRecord.from_settings_param_detailed_record(
+                    r,
+                    probability_two_random_records_match=self.core_model_settings.probability_two_random_records_match,
+                    iteration=iteration,
                 )
+                for r in core_model_settings.parameters_as_detailed_records
+            ]
 
             output_records.extend(records)
         return output_records
@@ -370,7 +393,7 @@ def match_weights_interactive_history_chart(self) -> ChartReturnType:
         Returns:
             An interactive Altair chart.
         """
-        records = self._iteration_history_records
+        records = list(map(lambda rec: rec.as_dict(), self._iteration_history_records))
         return match_weights_interactive_history_chart(
             records, blocking_rule=self._blocking_rule_for_training.blocking_rule_sql
         )
@@ -382,7 +405,7 @@ def m_u_values_interactive_history_chart(self) -> ChartReturnType:
         Returns:
             An interactive Altair chart.
         """
-        records = self._iteration_history_records
+        records = list(map(lambda rec: rec.as_dict(), self._iteration_history_records))
         return m_u_parameters_interactive_history_chart(records)
 
     def __repr__(self):
diff --git a/splink/internals/settings.py b/splink/internals/settings.py
index 2d417e3f7c..40c6029796 100644
--- a/splink/internals/settings.py
+++ b/splink/internals/settings.py
@@ -595,12 +595,16 @@ def _as_completed_dict(self):
         }
 
     def match_weights_chart(self, as_dict=False):
-        records = self._parameters_as_detailed_records
+        records = list(
+            map(lambda rec: rec.as_dict(), self._parameters_as_detailed_records)
+        )
 
         return match_weights_chart(records, as_dict=as_dict)
 
     def m_u_parameters_chart(self, as_dict=False):
-        records = self._parameters_as_detailed_records
+        records = list(
+            map(lambda rec: rec.as_dict(), self._parameters_as_detailed_records)
+        )
         return m_u_parameters_chart(records, as_dict=as_dict)
 
     def _columns_without_estimated_parameters_message(self):

From 201bfccd959192a921a8058ded7f06bd0c569955 Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Tue, 17 Feb 2026 17:16:56 +0000
Subject: [PATCH 14/20] comparison_match_weights_chart using dataclasses
 directly

---
 splink/internals/charts.py     | 23 ++++++++++++++++++-----
 splink/internals/comparison.py |  2 +-
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/splink/internals/charts.py b/splink/internals/charts.py
index d48b1981de..6d66cf4f34 100644
--- a/splink/internals/charts.py
+++ b/splink/internals/charts.py
@@ -3,8 +3,10 @@
 import json
 import math
 import os
-from typing import TYPE_CHECKING, Any, Dict, Union
+from collections.abc import Iterable
+from typing import TYPE_CHECKING, Any, Dict, Protocol, Union
 
+from splink.internals.comparison_level import ComparisonLevelDetailedRecord
 from splink.internals.misc import read_resource
 from splink.internals.waterfall_chart import records_to_waterfall_data
 
@@ -41,6 +43,14 @@ def altair_or_json(
     return chart_dict
 
 
+class AsDictable(Protocol):
+    def as_dict(self) -> dict[str, Any]: ...
+
+
+def list_items_as_dicts(lst: Iterable[AsDictable]) -> list[dict[str, Any]]:
+    return list(map(lambda item: item.as_dict(), lst))
+
+
 iframe_message = """
 To view in Jupyter you can use the following command:
 
@@ -110,18 +120,21 @@ def match_weights_chart(records, as_dict=False):
     return altair_or_json(chart, as_dict=as_dict)
 
 
-def comparison_match_weights_chart(records, as_dict=False):
+def comparison_match_weights_chart(
+    records: list[ComparisonLevelDetailedRecord], as_dict: bool = False
+) -> ChartReturnType:
     chart_path = "match_weights_interactive_history.json"
     chart = load_chart_definition(chart_path)
 
     # Remove iteration history since this is a static chart
-    del chart["vconcat"][0]
+    # TODO: some render issue if we remove empty top panel, so leave for now
+    # del chart["vconcat"][0]
     del chart["params"]
     del chart["transform"]
 
     chart["title"]["text"] = "Comparison summary"
-    records = [r for r in records if r["comparison_vector_value"] != -1]
-    chart["data"]["values"] = records
+    records = [r for r in records if r.comparison_vector_value != -1]
+    chart["data"]["values"] = list_items_as_dicts(records)
     return altair_or_json(chart, as_dict=as_dict)
 
 
diff --git a/splink/internals/comparison.py b/splink/internals/comparison.py
index b8988a9934..a3e9857499 100644
--- a/splink/internals/comparison.py
+++ b/splink/internals/comparison.py
@@ -467,5 +467,5 @@ def match_weights_chart(self, as_dict=False):
         """Display a chart of comparison levels of the comparison"""
         from splink.internals.charts import comparison_match_weights_chart
 
-        records = list(map(lambda rec: rec.as_dict(), self._as_detailed_records))
+        records = self._as_detailed_records
         return comparison_match_weights_chart(records, as_dict=as_dict)

From 8fefe1ed656d706c1b9b305aa5063442266cdcc0 Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Tue, 17 Feb 2026 17:17:06 +0000
Subject: [PATCH 15/20] test comparison_match_weight_charts

---
 tests/test_charts.py | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/tests/test_charts.py b/tests/test_charts.py
index 455b6ac837..b85cb33114 100644
--- a/tests/test_charts.py
+++ b/tests/test_charts.py
@@ -142,6 +142,24 @@ def test_m_u_charts(dialect, test_helpers):
     linker.visualisations.match_weights_chart()
 
 
+@mark_with_dialects_excluding()
+def test_comparison_match_weight_charts(dialect, test_helpers):
+    settings = {
+        "link_type": "dedupe_only",
+        "comparisons": [
+            cl.ExactMatch("gender"),
+            cl.ExactMatch("tm_partial"),
+            cl.LevenshteinAtThresholds("surname", [1]),
+        ],
+    }
+    helper = test_helpers[dialect]
+
+    linker = helper.linker_with_registration(df, settings)
+
+    comp = linker._settings_obj.comparisons[0]
+    comp.match_weights_chart()
+
+
 @mark_with_dialects_excluding()
 def test_parameter_estimate_charts(dialect, test_helpers):
     settings = {

From 6b814c54ebde16495f8d0d7c5edc9528c127dee4 Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Tue, 17 Feb 2026 17:32:50 +0000
Subject: [PATCH 16/20] match weight charts using dataclass

---
 splink/internals/charts.py   | 11 +++++++----
 splink/internals/settings.py |  6 ++----
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/splink/internals/charts.py b/splink/internals/charts.py
index 6d66cf4f34..99a5c14b2f 100644
--- a/splink/internals/charts.py
+++ b/splink/internals/charts.py
@@ -8,6 +8,7 @@
 
 from splink.internals.comparison_level import ComparisonLevelDetailedRecord
 from splink.internals.misc import read_resource
+from splink.internals.settings import ModelParameterDetailedRecord
 from splink.internals.waterfall_chart import records_to_waterfall_data
 
 if TYPE_CHECKING:
@@ -96,7 +97,9 @@ def save_offline_chart(
         print(iframe_message.format(filename=filename))  # noqa: T201
 
 
-def match_weights_chart(records, as_dict=False):
+def match_weights_chart(
+    records: list[ModelParameterDetailedRecord], as_dict: bool = False
+) -> ChartReturnType:
     chart_path = "match_weights_interactive_history.json"
     chart = load_chart_definition(chart_path)
 
@@ -104,15 +107,15 @@ def match_weights_chart(records, as_dict=False):
     del chart["params"]
     del chart["transform"]
 
-    records = [r for r in records if r["comparison_vector_value"] != -1]
-    chart["data"]["values"] = records
+    records = [r for r in records if r.comparison_vector_value != -1]
 
     bayes_factors = [
         abs(l2bf)
         for r in records
-        if (l2bf := r["log2_bayes_factor"]) is not None and not math.isinf(l2bf)
+        if (l2bf := r.log2_bayes_factor) is not None and not math.isinf(l2bf)
     ]
     max_value = math.ceil(max(bayes_factors))
+    chart["data"]["values"] = list_items_as_dicts(records)
 
     chart["vconcat"][0]["encoding"]["x"]["scale"]["domain"] = [-max_value, max_value]
     chart["vconcat"][1]["encoding"]["x"]["scale"]["domain"] = [-max_value, max_value]
diff --git a/splink/internals/settings.py b/splink/internals/settings.py
index 40c6029796..d690d07c21 100644
--- a/splink/internals/settings.py
+++ b/splink/internals/settings.py
@@ -595,12 +595,10 @@ def _as_completed_dict(self):
         }
 
     def match_weights_chart(self, as_dict=False):
-        records = list(
-            map(lambda rec: rec.as_dict(), self._parameters_as_detailed_records)
+        return match_weights_chart(
+            self._parameters_as_detailed_records, as_dict=as_dict
         )
 
-        return match_weights_chart(records, as_dict=as_dict)
-
     def m_u_parameters_chart(self, as_dict=False):
         records = list(
             map(lambda rec: rec.as_dict(), self._parameters_as_detailed_records)

From 6360bac31efec8e470a654ed216b5c231dd99ac2 Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Tue, 17 Feb 2026 17:55:25 +0000
Subject: [PATCH 17/20] mu charts using dataclass

---
 splink/internals/charts.py   | 10 ++++++----
 splink/internals/settings.py |  5 ++---
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/splink/internals/charts.py b/splink/internals/charts.py
index 99a5c14b2f..a1cfc7c544 100644
--- a/splink/internals/charts.py
+++ b/splink/internals/charts.py
@@ -141,7 +141,9 @@ def comparison_match_weights_chart(
     return altair_or_json(chart, as_dict=as_dict)
 
 
-def m_u_parameters_chart(records, as_dict=False):
+def m_u_parameters_chart(
+    records: list[ModelParameterDetailedRecord], as_dict: bool = False
+) -> ChartReturnType:
     chart_path = "m_u_parameters_interactive_history.json"
     chart = load_chart_definition(chart_path)
 
@@ -152,10 +154,10 @@ def m_u_parameters_chart(records, as_dict=False):
     records = [
         r
         for r in records
-        if r["comparison_vector_value"] != -1
-        and r["comparison_name"] != "probability_two_random_records_match"
+        if r.comparison_vector_value != -1
+        and r.comparison_name != "probability_two_random_records_match"
     ]
-    chart["data"]["values"] = records
+    chart["data"]["values"] = list_items_as_dicts(records)
     return altair_or_json(chart, as_dict=as_dict)
 
 
diff --git a/splink/internals/settings.py b/splink/internals/settings.py
index d690d07c21..fce55ce66a 100644
--- a/splink/internals/settings.py
+++ b/splink/internals/settings.py
@@ -600,10 +600,9 @@ def match_weights_chart(self, as_dict=False):
         )
 
     def m_u_parameters_chart(self, as_dict=False):
-        records = list(
-            map(lambda rec: rec.as_dict(), self._parameters_as_detailed_records)
+        return m_u_parameters_chart(
+            self._parameters_as_detailed_records, as_dict=as_dict
         )
-        return m_u_parameters_chart(records, as_dict=as_dict)
 
     def _columns_without_estimated_parameters_message(self):
         message_lines = []

From 21a4ea52854b2bb19e4a8e6fce4f10e61a2a2f28 Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Wed, 18 Feb 2026 09:18:42 +0000
Subject: [PATCH 18/20] import only for type checking

---
 splink/internals/charts.py | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/splink/internals/charts.py b/splink/internals/charts.py
index a1cfc7c544..55c031fc89 100644
--- a/splink/internals/charts.py
+++ b/splink/internals/charts.py
@@ -4,19 +4,20 @@
 import math
 import os
 from collections.abc import Iterable
-from typing import TYPE_CHECKING, Any, Dict, Protocol, Union
+from typing import TYPE_CHECKING, Any, Protocol, Union
 
-from splink.internals.comparison_level import ComparisonLevelDetailedRecord
 from splink.internals.misc import read_resource
-from splink.internals.settings import ModelParameterDetailedRecord
 from splink.internals.waterfall_chart import records_to_waterfall_data
 
 if TYPE_CHECKING:
     from altair import SchemaBase
+
+    from splink.internals.comparison_level import ComparisonLevelDetailedRecord
+    from splink.internals.settings import ModelParameterDetailedRecord
 else:
     SchemaBase = None
 # type alias:
-ChartReturnType = Union[Dict[Any, Any], SchemaBase]
+ChartReturnType = Union[dict[Any, Any], SchemaBase]
 
 
 def load_chart_definition(filename):

From acbec497d34d064974bb2c4c7e5a1994c04e6a3d Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Wed, 18 Feb 2026 09:56:10 +0000
Subject: [PATCH 19/20] avoid kw only

not supported in 3.9, and as we only have 1 default arg, that's only instantiated in 1 place, it is not a big sacrifice to just set this value at the call site
---
 splink/internals/comparison_level.py    | 5 +++--
 splink/internals/em_training_session.py | 2 +-
 splink/internals/settings.py            | 2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/splink/internals/comparison_level.py b/splink/internals/comparison_level.py
index 85dcb0208c..0f4de99597 100644
--- a/splink/internals/comparison_level.py
+++ b/splink/internals/comparison_level.py
@@ -117,7 +117,7 @@ def _default_u_values(num_levels: int) -> list[float]:
     return u_vals
 
 
-@dataclass(kw_only=True)
+@dataclass
 class ComparisonLevelDetailedRecord:
     sql_condition: str | None
     label_for_charts: str
@@ -139,7 +139,7 @@ class ComparisonLevelDetailedRecord:
 
     comparison_vector_value: int
     max_comparison_vector_value: int
-    comparison_name: str | None = None
+    comparison_name: str | None
 
     def as_dict(self):
         return asdict(self)
@@ -786,6 +786,7 @@ def _as_detailed_record(
             bayes_factor_description=self._bayes_factor_description,
             comparison_vector_value=self.comparison_vector_value,
             max_comparison_vector_value=comparison_num_levels - 1,
+            comparison_name=None,
         )
 
     def _parameter_estimates_as_records(
diff --git a/splink/internals/em_training_session.py b/splink/internals/em_training_session.py
index cbd25c9c12..1681972db1 100644
--- a/splink/internals/em_training_session.py
+++ b/splink/internals/em_training_session.py
@@ -41,7 +41,7 @@
     from splink.internals.splink_dataframe import SplinkDataFrame
 
 
-@dataclass(kw_only=True)
+@dataclass
 class ModelParameterIterationDetailedRecord(ModelParameterDetailedRecord):
     iteration: int
 
diff --git a/splink/internals/settings.py b/splink/internals/settings.py
index fce55ce66a..5a807d84d7 100644
--- a/splink/internals/settings.py
+++ b/splink/internals/settings.py
@@ -30,7 +30,7 @@ class ComparisonAndLevelDict(TypedDict):
     comparison: Comparison
 
 
-@dataclass(kw_only=True)
+@dataclass
 class ModelParameterDetailedRecord(ComparisonLevelDetailedRecord):
     probability_two_random_records_match: float
     comparison_sort_order: int

From cbc429f8f5bd413353127f88f3257fbb098f7317 Mon Sep 17 00:00:00 2001
From: ADBond <48208438+ADBond@users.noreply.github.com>
Date: Wed, 18 Feb 2026 11:16:12 +0000
Subject: [PATCH 20/20] iteration charts with dataclasses

---
 splink/internals/charts.py              | 27 ++++++++++++++++---------
 splink/internals/em_training_session.py |  7 +++----
 2 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/splink/internals/charts.py b/splink/internals/charts.py
index 55c031fc89..e3bcd392ae 100644
--- a/splink/internals/charts.py
+++ b/splink/internals/charts.py
@@ -13,6 +13,9 @@
     from altair import SchemaBase
 
     from splink.internals.comparison_level import ComparisonLevelDetailedRecord
+    from splink.internals.em_training_session import (
+        ModelParameterIterationDetailedRecord,
+    )
     from splink.internals.settings import ModelParameterDetailedRecord
 else:
     SchemaBase = None
@@ -170,39 +173,45 @@ def probability_two_random_records_match_iteration_chart(records, as_dict=False)
     return altair_or_json(chart, as_dict=as_dict)
 
 
-def match_weights_interactive_history_chart(records, as_dict=False, blocking_rule=None):
+def match_weights_interactive_history_chart(
+    records: list[ModelParameterIterationDetailedRecord],
+    as_dict: bool = False,
+    blocking_rule: str | None = None,
+) -> ChartReturnType:
     chart_path = "match_weights_interactive_history.json"
     chart = load_chart_definition(chart_path)
 
     chart["title"]["subtitle"] = f"Training session blocked on {blocking_rule}"
 
-    records = [r for r in records if r["comparison_vector_value"] != -1]
-    chart["data"]["values"] = records
+    records = [r for r in records if r.comparison_vector_value != -1]
 
     max_iteration = 0
     for r in records:
-        max_iteration = max(r["iteration"], max_iteration)
+        max_iteration = max(r.iteration, max_iteration)
+    chart["data"]["values"] = list_items_as_dicts(records)
 
     chart["params"][0]["bind"]["max"] = max_iteration
     chart["params"][0]["value"] = max_iteration
     return altair_or_json(chart, as_dict=as_dict)
 
 
-def m_u_parameters_interactive_history_chart(records, as_dict=False):
+def m_u_parameters_interactive_history_chart(
+    records: list[ModelParameterIterationDetailedRecord], as_dict: bool = False
+) -> ChartReturnType:
     chart_path = "m_u_parameters_interactive_history.json"
     chart = load_chart_definition(chart_path)
     records = [
         r
         for r in records
-        if r["comparison_vector_value"] != -1
-        and r["comparison_name"] != "probability_two_random_records_match"
+        if r.comparison_vector_value != -1
+        and r.comparison_name != "probability_two_random_records_match"
     ]
-    chart["data"]["values"] = records
 
     max_iteration = 0
     for r in records:
-        max_iteration = max(r["iteration"], max_iteration)
+        max_iteration = max(r.iteration, max_iteration)
 
+    chart["data"]["values"] = list_items_as_dicts(records)
     chart["params"][0]["bind"]["max"] = max_iteration
     chart["params"][0]["value"] = max_iteration
     return altair_or_json(chart, as_dict=as_dict)
diff --git a/splink/internals/em_training_session.py b/splink/internals/em_training_session.py
index 1681972db1..f50af9153b 100644
--- a/splink/internals/em_training_session.py
+++ b/splink/internals/em_training_session.py
@@ -393,9 +393,9 @@ def match_weights_interactive_history_chart(self) -> ChartReturnType:
         Returns:
             An interactive Altair chart.
         """
-        records = list(map(lambda rec: rec.as_dict(), self._iteration_history_records))
         return match_weights_interactive_history_chart(
-            records, blocking_rule=self._blocking_rule_for_training.blocking_rule_sql
+            self._iteration_history_records,
+            blocking_rule=self._blocking_rule_for_training.blocking_rule_sql,
         )
 
     def m_u_values_interactive_history_chart(self) -> ChartReturnType:
@@ -405,8 +405,7 @@ def m_u_values_interactive_history_chart(self) -> ChartReturnType:
         Returns:
             An interactive Altair chart.
         """
-        records = list(map(lambda rec: rec.as_dict(), self._iteration_history_records))
-        return m_u_parameters_interactive_history_chart(records)
+        return m_u_parameters_interactive_history_chart(self._iteration_history_records)
 
     def __repr__(self):
         deactivated_cols = ", ".join(