diff --git a/.ruby-version b/.ruby-version
index b347b11e..84d6c676 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.2.3
+3.4.10
diff --git a/.tool-versions b/.tool-versions
index 8ea25933..0b053141 100644
--- a/.tool-versions
+++ b/.tool-versions
@@ -1,5 +1,5 @@
 nodejs 22.23.2
-ruby 3.2.3
+ruby 3.4.10
 postgres 12.8
 mongodb 4.4.9
 redis 6.2.3
diff --git a/CLAUDE.md b/CLAUDE.md
index f6ea7157..f29b0a76 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -4,7 +4,7 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 Flaredown is a chronic-illness symptom tracker. It is a monorepo with three deployable apps:
 
-- `backend/` — Rails 7.1 API (Ruby 3.2.3), the only backend for all clients.
+- `backend/` — Rails 7.2 API (Ruby 3.4.10), the only backend for all clients.
 - `frontend/` — Ember.js 2.18 web app (the production web client at app.flaredown.com), proxies API calls to the backend.
 - `native/` — Expo / React Native + TypeScript app (newer, in-progress replacement for the Ember client).
 
diff --git a/README.md b/README.md
index deba00d4..21fb57d3 100644
--- a/README.md
+++ b/README.md
@@ -12,7 +12,7 @@ Help would be appreciated! Please join us in [slack #flaredown](https://join.sla
 * PostgreSQL 12.8
 * MongoDB 4.4.9
 * Redis 6.2.3
-* Ruby 3.2.3
+* Ruby 3.4.10
 * Node 22 (the frontend supports Node 18 and newer; `frontend/.nvmrc` pins the version CI builds against)
 
 ## Installation
diff --git a/backend/Dockerfile b/backend/Dockerfile
index 276ca765..746a44d1 100644
--- a/backend/Dockerfile
+++ b/backend/Dockerfile
@@ -1,4 +1,4 @@
-FROM ruby:3.2.3
+FROM ruby:3.4.10
 
 # set working directory
 WORKDIR /app
diff --git a/backend/Gemfile b/backend/Gemfile
index 2951a450..8cfdfd05 100644
--- a/backend/Gemfile
+++ b/backend/Gemfile
@@ -1,6 +1,6 @@
 source "https://rubygems.org"
 
-ruby "3.2.3"
+ruby "3.4.10"
 
 # Configuration management. keep on top of Gemfile
 gem "dotenv-rails", groups: %i[development test]
@@ -48,6 +48,13 @@ gem "countries", require: "countries/global"
 # Pusher Client
 gem "pusher"
 
+# Ruby 3.4 moved mutex_m from the default gems to the bundled gems, so it is no
+# longer requirable from inside the bundle unless it is in the Gemfile.
+# httpclient/auth.rb requires it, pusher requires httpclient, and the failure is
+# a partially-defined HTTPClient class rather than a LoadError -- webmock
+# swallows the LoadError and then dies aliasing a method that was never reached.
+gem "mutex_m"
+
 # ActiveRecord data translations
 gem "globalize", "~> 7.1"
 
diff --git a/backend/Gemfile.lock b/backend/Gemfile.lock
index 84c7b47d..1d12e08f 100644
--- a/backend/Gemfile.lock
+++ b/backend/Gemfile.lock
@@ -283,6 +283,7 @@ GEM
     multi_json (1.15.0)
     multi_xml (0.6.0)
     multipart-post (2.4.1)
+    mutex_m (0.3.0)
     nearest_time_zone (0.0.4)
       andand
       kdtree
@@ -331,9 +332,9 @@ GEM
     pry-byebug (3.10.1)
       byebug (~> 11.0)
       pry (>= 0.13, < 0.15)
-    pry-doc (1.5.0)
+    pry-doc (1.7.0)
       pry (~> 0.11)
-      yard (~> 0.9.11)
+      yard (~> 0.9.21)
     pry-rails (0.3.11)
       pry (>= 0.13.0)
     public_suffix (7.0.5)
@@ -546,6 +547,7 @@ DEPENDENCIES
   letter_opener
   mongoid (= 9.0.11)
   mongoid-rspec
+  mutex_m
   nearest_time_zone
   omniauth (~> 1.8)
   omniauth-facebook (~> 3.0)
@@ -574,7 +576,7 @@ DEPENDENCIES
   webmock
 
 RUBY VERSION
-   ruby 3.2.3p157
+   ruby 3.4.10p104
 
 BUNDLED WITH
    2.5.6