diff --git a/.circleci/config.yml b/.circleci/config.yml
index 56bc3e07e..f662a3702 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -1,8 +1,17 @@
 # https://circleci.com/docs/2.0/
 
-version: 2
+# We use version 2.1 of CircleCI's configuration format (the docs are still at
+# the 2.0 link) in order to have access to Windows executors. This means we
+# can't use dots in job names anymore. They have a new "parameters" feature
+# that is supposed to remove the need to have version numbers in job names (the
+# source of our dots), but switching to that is going to be a bigger refactor:
+#
+#   https://discuss.circleci.com/t/v2-1-job-name-validation/31123
+#   https://circleci.com/docs/2.0/reusing-config/
+#
+version: 2.1
+
 workflows:
-  version: 2
   ci:
     jobs:
       # Platforms
@@ -11,13 +20,13 @@ workflows:
           requires:
             - "debian-9"
 
-      - "ubuntu-20.04"
-      - "ubuntu-18.04":
+      - "ubuntu-20-04"
+      - "ubuntu-18-04":
           requires:
-            - "ubuntu-20.04"
-      - "ubuntu-16.04":
+            - "ubuntu-20-04"
+      - "ubuntu-16-04":
           requires:
-            - "ubuntu-20.04"
+            - "ubuntu-20-04"
 
       - "fedora-29"
       - "fedora-28":
@@ -26,13 +35,13 @@ workflows:
 
       - "centos-8"
 
-      - "nixos-19.09"
+      - "nixos-19-09"
 
       # Test against PyPy 2.7
-      - "pypy2.7-buster"
+      - "pypy27-buster"
 
       # Just one Python 3.6 configuration while the port is in-progress.
-      - "python3.6"
+      - "python36"
 
       # Other assorted tasks and configurations
       - "lint"
@@ -67,13 +76,13 @@ workflows:
     jobs:
       - "build-image-debian-8"
       - "build-image-debian-9"
-      - "build-image-ubuntu-16.04"
-      - "build-image-ubuntu-18.04"
-      - "build-image-ubuntu-20.04"
+      - "build-image-ubuntu-16-04"
+      - "build-image-ubuntu-18-04"
+      - "build-image-ubuntu-20-04"
       - "build-image-fedora-28"
       - "build-image-fedora-29"
       - "build-image-centos-8"
-      - "build-image-pypy-2.7-buster"
+      - "build-image-pypy27-buster"
       - "build-image-python36-ubuntu"
 
 
@@ -203,7 +212,7 @@ jobs:
         user: "nobody"
 
 
-  pypy2.7-buster:
+  pypy27-buster:
     <<: *DEBIAN
     docker:
       - image: "tahoelafsci/pypy:buster-py2"
@@ -260,21 +269,21 @@ jobs:
       - run: *RUN_TESTS
 
 
-  ubuntu-16.04:
+  ubuntu-16-04:
     <<: *DEBIAN
     docker:
       - image: "tahoelafsci/ubuntu:16.04-py2.7"
         user: "nobody"
 
 
-  ubuntu-18.04: &UBUNTU_18_04
+  ubuntu-18-04: &UBUNTU_18_04
     <<: *DEBIAN
     docker:
       - image: "tahoelafsci/ubuntu:18.04-py2.7"
         user: "nobody"
 
 
-  python3.6:
+  python36:
     <<: *UBUNTU_18_04
     docker:
       - image: "tahoelafsci/ubuntu:18.04-py3"
@@ -289,7 +298,7 @@ jobs:
       TAHOE_LAFS_TOX_ENVIRONMENT: "py36-coverage"
 
 
-  ubuntu-20.04:
+  ubuntu-20-04:
     <<: *DEBIAN
     docker:
       - image: "tahoelafsci/ubuntu:20.04"
@@ -331,7 +340,7 @@ jobs:
         user: "nobody"
 
 
-  nixos-19.09:
+  nixos-19-09:
     docker:
       # Run in a highly Nix-capable environment.
       - image: "nixorg/nix:circleci"
@@ -476,7 +485,7 @@ jobs:
       PYTHON_VERSION: "2.7"
 
 
-  build-image-ubuntu-16.04:
+  build-image-ubuntu-16-04:
     <<: *BUILD_IMAGE
 
     environment:
@@ -485,7 +494,7 @@ jobs:
       PYTHON_VERSION: "2.7"
 
 
-  build-image-ubuntu-18.04:
+  build-image-ubuntu-18-04:
     <<: *BUILD_IMAGE
 
     environment:
@@ -503,7 +512,7 @@ jobs:
       PYTHON_VERSION: "3"
 
 
-  build-image-ubuntu-20.04:
+  build-image-ubuntu-20-04:
     <<: *BUILD_IMAGE
 
     environment:
@@ -539,7 +548,7 @@ jobs:
       TAG: "29"
 
 
-  build-image-pypy-2.7-buster:
+  build-image-pypy27-buster:
     <<: *BUILD_IMAGE
 
     environment:
diff --git a/newsfragments/3406.minor b/newsfragments/3406.minor
new file mode 100644
index 000000000..e69de29bb