diff --git a/.gitmodules b/.gitmodules
index 0310b9efd9..4de7814a55 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -28,7 +28,7 @@
[submodule "fates"]
path = src/fates
url = https://github.com/NGEET/fates
-fxtag = sci.1.83.1_api.39.0.0
+fxtag = sci.1.84.0_api.40.0.0
fxrequired = AlwaysRequired
# Standard Fork to compare to with "git fleximod test" to ensure personal forks aren't committed
fxDONOTUSEurl = https://github.com/NGEET/fates
diff --git a/bld/namelist_files/namelist_defaults_ctsm.xml b/bld/namelist_files/namelist_defaults_ctsm.xml
index 7adb380a61..fedfca8020 100644
--- a/bld/namelist_files/namelist_defaults_ctsm.xml
+++ b/bld/namelist_files/namelist_defaults_ctsm.xml
@@ -540,7 +540,7 @@ attributes from the config_cache.xml file (with keys converted to upper-case).
-lnd/clm2/paramdata/fates_params_api.38.0.0_14pft_c250226.nc
+lnd/clm2/paramdata/fates_params_api.40.0.0_14pft_c250512.nc
diff --git a/cime_config/testdefs/testlist_clm.xml b/cime_config/testdefs/testlist_clm.xml
index 953747ddbf..62a9f109ca 100644
--- a/cime_config/testdefs/testlist_clm.xml
+++ b/cime_config/testdefs/testlist_clm.xml
@@ -150,7 +150,7 @@
-
+
@@ -567,7 +567,7 @@
-
+
@@ -1330,7 +1330,7 @@
-
+
@@ -1406,7 +1406,7 @@
-
+
@@ -1602,7 +1602,7 @@
-
+
@@ -2999,7 +2999,7 @@
-
+
@@ -3261,7 +3261,7 @@
-
+
diff --git a/doc/ChangeLog b/doc/ChangeLog
index ab165f8136..49caf507b8 100644
--- a/doc/ChangeLog
+++ b/doc/ChangeLog
@@ -1,4 +1,90 @@
===============================================================
+Tag name: ctsm5.3.045
+Originator(s): glemieux (Gregory Lemieux, LBNL, glemieux@lbl.gov)
+Date: Tue May 20 11:56:15 MDT 2025
+One-line Summary: FATES default parameter update for API 40
+
+Purpose and description of changes
+----------------------------------
+
+Update the FATES default parameter and associated tag to API 40. This update
+includes changes to the default competitive exclusion parameter, sets the logging
+default to clear cut, and refactors the pft-specific phenology habit selection.
+
+Significant changes to scientifically-supported configurations
+--------------------------------------------------------------
+
+Does this tag change answers significantly for any of the following physics configurations?
+(Details of any changes will be given in the "Answer changes" section below.)
+
+ [Put an [X] in the box for any configuration with significant answer changes.]
+
+[ ] clm6_0
+
+[ ] clm5_0
+
+[ ] ctsm5_0-nwp
+
+[ ] clm4_5
+
+
+Notes of particular relevance for users
+---------------------------------------
+Changes to the datasets (e.g., parameter, surface or initial files):
+ The FATES default parameter file update unifies the pft-level phenology habit from three
+ separate on/off switches, into one per-pft integer selection switch, fates_phen_leaf_habit
+
+Notes of particular relevance for developers:
+---------------------------------------------
+Changes to tests or testing:
+ Wall clock time increased by ten minutes for a select set of izumi tests.
+
+
+Testing summary:
+----------------
+
+ regular tests (aux_clm: https://github.com/ESCOMP/CTSM/wiki/System-Testing-Guide#pre-merge-system-testing):
+
+ derecho ----- OK
+ izumi -------
+
+ fates tests: (give name of baseline if different from CTSM tagname, normally fates baselines are fates--)
+ derecho ----- OK
+ izumi ------- OK
+
+ any other testing (give details below):
+
+ ctsm_sci
+ derecho ----
+
+If the tag used for baseline comparisons was NOT the previous tag, note that here:
+
+ fates tested against fates-sci.1.84.0_api.40.0.0-ctsm5.3.042-pr1358-1359
+
+Answer changes
+--------------
+
+Changes answers relative to baseline: yes, fates tests only
+
+ FIELDLIST differences due to competetive exclusion parameter update triggering inclusion
+ of a previously inactive history output. Numerical preciscion differences in a subset of
+ carbon flux outputs. Long term tests demonstrate roundoff differences propagated due
+ to competetive exclusion parameter update.
+
+Other details
+-------------
+
+List any git submodules updated (cime, rtm, mosart, cism, fates, etc.):
+ fates: sci.1.83.1_api.39.0.0 -> sci.1.84.0_api.40.0.0
+
+Pull Requests that document the changes (include PR ids):
+(https://github.com/ESCOMP/ctsm/pull)
+
+https://github.com/ESCOMP/CTSM/pull/3087
+https://github.com/NGEET/fates/pull/1406
+
+===============================================================
+===============================================================
Tag name: ctsm5.3.044
Originator(s): slevis (Samuel Levis,UCAR/TSS,303-665-1310)
Date: Wed 14 May 2025 11:42:41 AM MDT
diff --git a/doc/ChangeSum b/doc/ChangeSum
index 85192e7d5a..75660abd7b 100644
--- a/doc/ChangeSum
+++ b/doc/ChangeSum
@@ -1,5 +1,6 @@
Tag Who Date Summary
============================================================================================================================
+ ctsm5.3.045 glemieux 05/20/2025 FATES default parameter update for API 40
ctsm5.3.044 slevis 05/14/2025 Introduce time-evolving LEAFCN_TARGET as function of leafcn param
ctsm5.3.043 slevis 05/09/2025 Merge b4b-dev
ctsm5.3.042 glemieux 05/08/2025 Update FATES tag, tests and address namelist option bug
diff --git a/src/fates b/src/fates
index fe782ba4f8..c319e6759a 160000
--- a/src/fates
+++ b/src/fates
@@ -1 +1 @@
-Subproject commit fe782ba4f851f8c8bfac8a89607e7c05bd397553
+Subproject commit c319e6759a7396246ddd34fc7dd46374e344d4a4