diff --git a/docs/overview/changelog.md b/docs/overview/changelog.md
index 4d735dac26..cce800e80d 100644
--- a/docs/overview/changelog.md
+++ b/docs/overview/changelog.md
@@ -142,6 +142,8 @@ _Unreleased_
 - Zulip's incoming email integration was simplified to no longer use
   `postfix`. Installations using the integration will automatically
   uninstall `postfix` when upgraded.
+- The `SOCIAL_AUTH_SYNC_CUSTOM_ATTRS_DICT` setting has been removed.
+  It was deprecated in favor of `SOCIAL_AUTH_SYNC_ATTRS_DICT` in 10.0.
 
 ## Zulip Server 10.x series
 
diff --git a/zproject/computed_settings.py b/zproject/computed_settings.py
index 79efebdd72..746173f29f 100644
--- a/zproject/computed_settings.py
+++ b/zproject/computed_settings.py
@@ -65,7 +65,6 @@ from .configured_settings import (
     SOCIAL_AUTH_SAML_SECURITY_CONFIG,
     SOCIAL_AUTH_SUBDOMAIN,
     SOCIAL_AUTH_SYNC_ATTRS_DICT,
-    SOCIAL_AUTH_SYNC_CUSTOM_ATTRS_DICT,
     STATIC_URL,
     SUBMIT_USAGE_STATISTICS,
     TORNADO_PORTS,
@@ -1216,17 +1215,6 @@ def ensure_dict_path(d: dict[str, Any], keys: list[str]) -> None:
         d = d[key]
 
 
-# Merge SOCIAL_AUTH_SYNC_CUSTOM_ATTRS_DICT into SOCIAL_AUTH_SYNC_ATTRS_DICT.
-# This is compat code for the original SOCIAL_AUTH_CUSTOM_ATTRS_DICT setting.
-# TODO/compatibility: Remove this for release Zulip 10.0.
-for subdomain, dict_for_subdomain in SOCIAL_AUTH_SYNC_CUSTOM_ATTRS_DICT.items():
-    for backend_name, custom_attrs_map in dict_for_subdomain.items():
-        ensure_dict_path(SOCIAL_AUTH_SYNC_ATTRS_DICT, [subdomain, backend_name])
-        for custom_attr_name, source_attr_name in custom_attrs_map.items():
-            SOCIAL_AUTH_SYNC_ATTRS_DICT[subdomain][backend_name][f"custom__{custom_attr_name}"] = (
-                source_attr_name
-            )
-
 SOCIAL_AUTH_PIPELINE = [
     "social_core.pipeline.social_auth.social_details",
     "zproject.backends.social_auth_associate_user",
diff --git a/zproject/default_settings.py b/zproject/default_settings.py
index f2bb9b2227..029028a048 100644
--- a/zproject/default_settings.py
+++ b/zproject/default_settings.py
@@ -112,7 +112,6 @@ SOCIAL_AUTH_APPLE_EMAIL_AS_USERNAME = True
 SOCIAL_AUTH_OIDC_ENABLED_IDPS: dict[str, OIDCIdPConfigDict] = {}
 SOCIAL_AUTH_OIDC_FULL_NAME_VALIDATED = False
 
-SOCIAL_AUTH_SYNC_CUSTOM_ATTRS_DICT: dict[str, dict[str, dict[str, str]]] = {}
 SOCIAL_AUTH_SYNC_ATTRS_DICT: dict[str, dict[str, dict[str, str]]] = {}
 
 # Other auth
diff --git a/zproject/prod_settings_template.py b/zproject/prod_settings_template.py
index 15016a304c..55da889186 100644
--- a/zproject/prod_settings_template.py
+++ b/zproject/prod_settings_template.py
@@ -441,8 +441,8 @@ SOCIAL_AUTH_SAML_ENABLED_IDPS: dict[str, Any] = {
         "attr_username": "email",
         "attr_email": "email",
         ## List of additional attributes to fetch from the SAMLResponse.
-        ## These attributes will be available for synchronizing custom profile fields.
-        ## in SOCIAL_AUTH_SYNC_CUSTOM_ATTRS_DICT.
+        ## These attributes will be available for synchronizing user profile fields.
+        ## in SOCIAL_AUTH_SYNC_ATTRS_DICT.
         # "extra_attrs": ["title", "mobilePhone", "zulip_role"],
         ##
         ## The "x509cert" attribute is automatically read from