diff --git a/changelog.d/18727.misc b/changelog.d/18727.misc
new file mode 100644
index 0000000000..884ec72a2f
--- /dev/null
+++ b/changelog.d/18727.misc
@@ -0,0 +1 @@
+Bump minimum version bound on Twisted to 21.2.0.
\ No newline at end of file
diff --git a/poetry.lock b/poetry.lock
index 1928fed975..5cb4127737 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -39,7 +39,7 @@ description = "The ultimate Python library in building OAuth and OpenID Connect
 optional = true
 python-versions = ">=3.9"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"jwt\" or extra == \"oidc\""
+markers = "extra == \"oidc\" or extra == \"jwt\" or extra == \"all\""
 files = [
     {file = "authlib-1.6.1-py2.py3-none-any.whl", hash = "sha256:e9d2031c34c6309373ab845afc24168fe9e93dc52d252631f52642f21f5ed06e"},
     {file = "authlib-1.6.1.tar.gz", hash = "sha256:4dffdbb1460ba6ec8c17981a4c67af7d8af131231b5a36a88a1e8c80c111cdfd"},
@@ -435,7 +435,7 @@ description = "XML bomb protection for Python stdlib modules"
 optional = true
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"saml2\""
+markers = "extra == \"saml2\" or extra == \"all\""
 files = [
     {file = "defusedxml-0.7.1-py2.py3-none-any.whl", hash = "sha256:a352e7e428770286cc899e2542b6cdaedb2b4953ff269a210103ec58f6198a61"},
     {file = "defusedxml-0.7.1.tar.gz", hash = "sha256:1bb3032db185915b62d7c6209c5a8792be6a32ab2fedacc84e01b52c51aa3e69"},
@@ -478,7 +478,7 @@ description = "XPath 1.0/2.0/3.0/3.1 parsers and selectors for ElementTree and l
 optional = true
 python-versions = ">=3.7"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"saml2\""
+markers = "extra == \"saml2\" or extra == \"all\""
 files = [
     {file = "elementpath-4.1.5-py3-none-any.whl", hash = "sha256:2ac1a2fb31eb22bbbf817f8cf6752f844513216263f0e3892c8e79782fe4bb55"},
     {file = "elementpath-4.1.5.tar.gz", hash = "sha256:c2d6dc524b29ef751ecfc416b0627668119d8812441c555d7471da41d4bacb8d"},
@@ -528,7 +528,7 @@ description = "Python wrapper for hiredis"
 optional = true
 python-versions = ">=3.8"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"redis\""
+markers = "extra == \"redis\" or extra == \"all\""
 files = [
     {file = "hiredis-3.2.1-cp310-cp310-macosx_10_15_universal2.whl", hash = "sha256:add17efcbae46c5a6a13b244ff0b4a8fa079602ceb62290095c941b42e9d5dec"},
     {file = "hiredis-3.2.1-cp310-cp310-macosx_10_15_x86_64.whl", hash = "sha256:5fe955cc4f66c57df1ae8e5caf4de2925d43b5efab4e40859662311d1bcc5f54"},
@@ -865,7 +865,7 @@ description = "Jaeger Python OpenTracing Tracer implementation"
 optional = true
 python-versions = ">=3.7"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"opentracing\""
+markers = "extra == \"opentracing\" or extra == \"all\""
 files = [
     {file = "jaeger-client-4.8.0.tar.gz", hash = "sha256:3157836edab8e2c209bd2d6ae61113db36f7ee399e66b1dcbb715d87ab49bfe0"},
 ]
@@ -1003,7 +1003,7 @@ description = "A strictly RFC 4510 conforming LDAP V3 pure Python client library
 optional = true
 python-versions = "*"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"matrix-synapse-ldap3\""
+markers = "extra == \"matrix-synapse-ldap3\" or extra == \"all\""
 files = [
     {file = "ldap3-2.9.1-py2.py3-none-any.whl", hash = "sha256:5869596fc4948797020d3f03b7939da938778a0f9e2009f7a072ccf92b8e8d70"},
     {file = "ldap3-2.9.1.tar.gz", hash = "sha256:f3e7fc4718e3f09dda568b57100095e0ce58633bcabbed8667ce3f8fbaa4229f"},
@@ -1019,7 +1019,7 @@ description = "Powerful and Pythonic XML processing library combining libxml2/li
 optional = true
 python-versions = ">=3.8"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"url-preview\""
+markers = "extra == \"url-preview\" or extra == \"all\""
 files = [
     {file = "lxml-6.0.0-cp310-cp310-macosx_10_9_universal2.whl", hash = "sha256:35bc626eec405f745199200ccb5c6b36f202675d204aa29bb52e27ba2b71dea8"},
     {file = "lxml-6.0.0-cp310-cp310-macosx_10_9_x86_64.whl", hash = "sha256:246b40f8a4aec341cbbf52617cad8ab7c888d944bfe12a6abd2b1f6cfb6f6082"},
@@ -1260,7 +1260,7 @@ description = "An LDAP3 auth provider for Synapse"
 optional = true
 python-versions = ">=3.7"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"matrix-synapse-ldap3\""
+markers = "extra == \"matrix-synapse-ldap3\" or extra == \"all\""
 files = [
     {file = "matrix-synapse-ldap3-0.3.0.tar.gz", hash = "sha256:8bb6517173164d4b9cc44f49de411d8cebdb2e705d5dd1ea1f38733c4a009e1d"},
     {file = "matrix_synapse_ldap3-0.3.0-py3-none-any.whl", hash = "sha256:8b4d701f8702551e98cc1d8c20dbed532de5613584c08d0df22de376ba99159d"},
@@ -1493,7 +1493,7 @@ description = "OpenTracing API for Python. See documentation at http://opentraci
 optional = true
 python-versions = "*"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"opentracing\""
+markers = "extra == \"opentracing\" or extra == \"all\""
 files = [
     {file = "opentracing-2.4.0.tar.gz", hash = "sha256:a173117e6ef580d55874734d1fa7ecb6f3655160b8b8974a2a1e98e5ec9c840d"},
 ]
@@ -1699,7 +1699,7 @@ description = "psycopg2 - Python-PostgreSQL Database Adapter"
 optional = true
 python-versions = ">=3.8"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"postgres\""
+markers = "extra == \"postgres\" or extra == \"all\""
 files = [
     {file = "psycopg2-2.9.10-cp310-cp310-win32.whl", hash = "sha256:5df2b672140f95adb453af93a7d669d7a7bf0a56bcd26f1502329166f4a61716"},
     {file = "psycopg2-2.9.10-cp310-cp310-win_amd64.whl", hash = "sha256:c6f7b8561225f9e711a9c47087388a97fdc948211c10a4bccbf0ba68ab7b3b5a"},
@@ -1720,7 +1720,7 @@ description = ".. image:: https://travis-ci.org/chtd/psycopg2cffi.svg?branch=mas
 optional = true
 python-versions = "*"
 groups = ["main"]
-markers = "platform_python_implementation == \"PyPy\" and (extra == \"all\" or extra == \"postgres\")"
+markers = "platform_python_implementation == \"PyPy\" and (extra == \"postgres\" or extra == \"all\")"
 files = [
     {file = "psycopg2cffi-2.9.0.tar.gz", hash = "sha256:7e272edcd837de3a1d12b62185eb85c45a19feda9e62fa1b120c54f9e8d35c52"},
 ]
@@ -1736,7 +1736,7 @@ description = "A Simple library to enable psycopg2 compatability"
 optional = true
 python-versions = "*"
 groups = ["main"]
-markers = "platform_python_implementation == \"PyPy\" and (extra == \"all\" or extra == \"postgres\")"
+markers = "platform_python_implementation == \"PyPy\" and (extra == \"postgres\" or extra == \"all\")"
 files = [
     {file = "psycopg2cffi-compat-1.1.tar.gz", hash = "sha256:d25e921748475522b33d13420aad5c2831c743227dc1f1f2585e0fdb5c914e05"},
 ]
@@ -1996,7 +1996,7 @@ description = "A development tool to measure, monitor and analyze the memory beh
 optional = true
 python-versions = ">=3.6"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"cache-memory\""
+markers = "extra == \"cache-memory\" or extra == \"all\""
 files = [
     {file = "Pympler-1.0.1-py3-none-any.whl", hash = "sha256:d260dda9ae781e1eab6ea15bacb84015849833ba5555f141d2d9b7b7473b307d"},
     {file = "Pympler-1.0.1.tar.gz", hash = "sha256:993f1a3599ca3f4fcd7160c7545ad06310c9e12f70174ae7ae8d4e25f6c5d3fa"},
@@ -2056,7 +2056,7 @@ description = "Python implementation of SAML Version 2 Standard"
 optional = true
 python-versions = ">=3.9,<4.0"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"saml2\""
+markers = "extra == \"saml2\" or extra == \"all\""
 files = [
     {file = "pysaml2-7.5.0-py3-none-any.whl", hash = "sha256:bc6627cc344476a83c757f440a73fda1369f13b6fda1b4e16bca63ffbabb5318"},
     {file = "pysaml2-7.5.0.tar.gz", hash = "sha256:f36871d4e5ee857c6b85532e942550d2cf90ea4ee943d75eb681044bbc4f54f7"},
@@ -2081,7 +2081,7 @@ description = "Extensions to the standard Python datetime module"
 optional = true
 python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,>=2.7"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"saml2\""
+markers = "extra == \"saml2\" or extra == \"all\""
 files = [
     {file = "python-dateutil-2.8.2.tar.gz", hash = "sha256:0123cacc1627ae19ddf3c27a5de5bd67ee4586fbdd6440d9748f8abb483d3e86"},
     {file = "python_dateutil-2.8.2-py2.py3-none-any.whl", hash = "sha256:961d03dc3453ebbc59dbdea9e4e11c5651520a876d0f4db161e8674aae935da9"},
@@ -2109,7 +2109,7 @@ description = "World timezone definitions, modern and historical"
 optional = true
 python-versions = "*"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"saml2\""
+markers = "extra == \"saml2\" or extra == \"all\""
 files = [
     {file = "pytz-2022.7.1-py2.py3-none-any.whl", hash = "sha256:78f4f37d8198e0627c5f1143240bb0206b8691d8d7ac6d78fee88b78733f8c4a"},
     {file = "pytz-2022.7.1.tar.gz", hash = "sha256:01a0681c4b9684a28304615eba55d1ab31ae00bf68ec157ec3708a8182dbbcd0"},
@@ -2474,7 +2474,7 @@ description = "Python client for Sentry (https://sentry.io)"
 optional = true
 python-versions = ">=3.6"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"sentry\""
+markers = "extra == \"sentry\" or extra == \"all\""
 files = [
     {file = "sentry_sdk-2.32.0-py2.py3-none-any.whl", hash = "sha256:6cf51521b099562d7ce3606da928c473643abe99b00ce4cb5626ea735f4ec345"},
     {file = "sentry_sdk-2.32.0.tar.gz", hash = "sha256:9016c75d9316b0f6921ac14c8cd4fb938f26002430ac5be9945ab280f78bec6b"},
@@ -2662,7 +2662,7 @@ description = "Tornado IOLoop Backed Concurrent Futures"
 optional = true
 python-versions = "*"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"opentracing\""
+markers = "extra == \"opentracing\" or extra == \"all\""
 files = [
     {file = "threadloop-1.0.2-py2-none-any.whl", hash = "sha256:5c90dbefab6ffbdba26afb4829d2a9df8275d13ac7dc58dccb0e279992679599"},
     {file = "threadloop-1.0.2.tar.gz", hash = "sha256:8b180aac31013de13c2ad5c834819771992d350267bddb854613ae77ef571944"},
@@ -2678,7 +2678,7 @@ description = "Python bindings for the Apache Thrift RPC system"
 optional = true
 python-versions = "*"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"opentracing\""
+markers = "extra == \"opentracing\" or extra == \"all\""
 files = [
     {file = "thrift-0.16.0.tar.gz", hash = "sha256:2b5b6488fcded21f9d312aa23c9ff6a0195d0f6ae26ddbd5ad9e3e25dfc14408"},
 ]
@@ -2740,7 +2740,7 @@ description = "Tornado is a Python web framework and asynchronous networking lib
 optional = true
 python-versions = ">=3.9"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"opentracing\""
+markers = "extra == \"opentracing\" or extra == \"all\""
 files = [
     {file = "tornado-6.5-cp39-abi3-macosx_10_9_universal2.whl", hash = "sha256:f81067dad2e4443b015368b24e802d0083fecada4f0a4572fdb72fc06e54a9a6"},
     {file = "tornado-6.5-cp39-abi3-macosx_10_9_x86_64.whl", hash = "sha256:9ac1cbe1db860b3cbb251e795c701c41d343f06a96049d6274e7c77559117e41"},
@@ -2877,7 +2877,7 @@ description = "non-blocking redis client for python"
 optional = true
 python-versions = "*"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"redis\""
+markers = "extra == \"redis\" or extra == \"all\""
 files = [
     {file = "txredisapi-1.4.11-py3-none-any.whl", hash = "sha256:ac64d7a9342b58edca13ef267d4fa7637c1aa63f8595e066801c1e8b56b22d0b"},
     {file = "txredisapi-1.4.11.tar.gz", hash = "sha256:3eb1af99aefdefb59eb877b1dd08861efad60915e30ad5bf3d5bf6c5cedcdbc6"},
@@ -3208,7 +3208,7 @@ description = "An XML Schema validator and decoder"
 optional = true
 python-versions = ">=3.7"
 groups = ["main"]
-markers = "extra == \"all\" or extra == \"saml2\""
+markers = "extra == \"saml2\" or extra == \"all\""
 files = [
     {file = "xmlschema-2.4.0-py3-none-any.whl", hash = "sha256:dc87be0caaa61f42649899189aab2fd8e0d567f2cf548433ba7b79278d231a4a"},
     {file = "xmlschema-2.4.0.tar.gz", hash = "sha256:d74cd0c10866ac609e1ef94a5a69b018ad16e39077bc6393408b40c6babee793"},
@@ -3352,4 +3352,4 @@ url-preview = ["lxml"]
 [metadata]
 lock-version = "2.1"
 python-versions = "^3.9.0"
-content-hash = "b1a0f4708465fd597d0bc7ebb09443ce0e2613cd58a33387a28036249f26856b"
+content-hash = "d2560fb09c99bf87690749ad902753cfa3f3063bd14cd9d0c0f37ca9e89a7757"
diff --git a/pyproject.toml b/pyproject.toml
index 11bc7277fe..5139181482 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -178,8 +178,13 @@ signedjson = "^1.1.0"
 service-identity = ">=18.1.0"
 # Twisted 18.9 introduces some logger improvements that the structured
 # logger utilises
-Twisted = {extras = ["tls"], version = ">=18.9.0"}
-treq = ">=15.1"
+# Twisted 19.7.0 moves test helpers to a new module and deprecates the old location.
+# Twisted 21.2.0 introduces contextvar support.
+# We could likely bump this to 22.1 without making distro packagers'
+# lives hard (as of 2025-07, distro support is Ubuntu LTS: 22.1, Debian stable: 22.4,
+# RHEL 9: 22.10)
+Twisted = {extras = ["tls"], version = ">=21.2.0"}
+treq = ">=21.5.0"
 # Twisted has required pyopenssl 16.0 since about Twisted 16.6.
 pyOpenSSL = ">=16.0.0"
 PyYAML = ">=5.3"