diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 796545a..3688874 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -4,6 +4,10 @@ Change Log
 
 This document records all notable changes to `stellar-model <https://github.com/StellarCN/stellar-model/>`_.
 
+0.2.1b0 (Horizon v2.8.3)
+------------------------
+* fix: make `Account.last_modified_time` optional. (`#19 <https://github.com/StellarCN/stellar-model/pull/19/>`_)
+
 0.2.0b0 (Horizon v2.5.2)
 ------------------------
 * feat: add support for muxed account.
diff --git a/README.rst b/README.rst
index 7c87312..4961b44 100644
--- a/README.rst
+++ b/README.rst
@@ -13,9 +13,9 @@ stellar-model
     :alt: PyPI
     :target: https://pypi.python.org/pypi/stellar-model
 
-.. image:: https://img.shields.io/badge/Supported%20Horizon%20Version-2.2.0-blue?style=flat
+.. image:: https://img.shields.io/badge/Supported%20Horizon%20Version-2.8.3-blue?style=flat
     :alt: Supported Horizon Version
-    :target: https://github.com/stellar/go/releases/tag/horizon-v2.2.0
+    :target: https://github.com/stellar/go/releases/tag/horizon-v2.8.3
 
 .. image:: https://img.shields.io/badge/python-3.6%20%7C%203.7%20%7C%203.8%20%7C%203.9-blue?style=flat
     :alt: Python - Version
@@ -32,9 +32,12 @@ development experience in the editor with things like code completion, type hint
 Installing
 ==========
 
+You need to choose a suitable stellar-model version according to the Horizon version number you are using.
+Please check the list `here <https://github.com/StellarCN/stellar-model/issues/20/>`_.
+
 .. code-block:: text
 
-    pip install stellar-model==0.2.0b0
+    pip install stellar-model==0.2.1b0
 
 Example
 =======
diff --git a/pyproject.toml b/pyproject.toml
index 3cd10d0..116ede0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "stellar-model"
-version = "0.2.0b0"
+version = "0.2.1b0"
 description = "Parse the raw Stellar data into Python models."
 authors = ["overcat <4catcode@gmail.com>"]
 readme = "README.rst"
diff --git a/stellar_model/__init__.py b/stellar_model/__init__.py
index a08e7b4..f705caf 100644
--- a/stellar_model/__init__.py
+++ b/stellar_model/__init__.py
@@ -1,5 +1,5 @@
-__version__ = "0.2.0b0"
-__supported_horizon_version__ = "2.2.0"
+__version__ = "0.2.1b0"
+__supported_horizon_version__ = "2.8.3"
 __url__ = "https://github.com/StellarCN/stellar-model"
 __issues__ = f"{__url__}/issues"