diff --git a/lib/httpx/plugins/circuit_breaker.rb b/lib/httpx/plugins/circuit_breaker.rb
index 52f58846..2ac33a7e 100644
--- a/lib/httpx/plugins/circuit_breaker.rb
+++ b/lib/httpx/plugins/circuit_breaker.rb
@@ -51,13 +51,13 @@ module HTTPX
 
           # run all requests through the circuit breaker, see if the circuit is
           # open for any of them.
-          real_requests = requests.each_with_object([]) do |req, real_reqs|
+          real_requests = requests.each_with_index.with_object([]) do |(req, idx), real_reqs|
             short_circuit_response = @circuit_store.try_respond(req)
             if short_circuit_response.nil?
               real_reqs << req
               next
             end
-            short_circuit_responses[requests.index(req)] = short_circuit_response
+            short_circuit_responses[idx] = short_circuit_response
           end
 
           # run requests for the remainder
@@ -90,6 +90,7 @@ module HTTPX
             @circuit_store.try_open(request.uri, response)
           else
             @circuit_store.try_close(request.uri)
+            nil
           end
         end
       end
diff --git a/lib/httpx/plugins/circuit_breaker/circuit_store.rb b/lib/httpx/plugins/circuit_breaker/circuit_store.rb
index 707bee45..b04c7a61 100644
--- a/lib/httpx/plugins/circuit_breaker/circuit_store.rb
+++ b/lib/httpx/plugins/circuit_breaker/circuit_store.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "mutex_m"
+
 module HTTPX::Plugins::CircuitBreaker
   using HTTPX::URIExtensions
 
@@ -13,18 +15,21 @@ module HTTPX::Plugins::CircuitBreaker
           options.circuit_breaker_half_open_drip_rate
         )
       end
+      @circuits.extend(Mutex_m)
     end
 
     def try_open(uri, response)
-      circuit = get_circuit_for_uri(uri)
+      circuit = @circuits.synchronize { get_circuit_for_uri(uri) }
 
       circuit.try_open(response)
     end
 
     def try_close(uri)
-      return unless @circuits.key?(uri.origin) || @circuits.key?(uri.to_s)
+      circuit = @circuits.synchronize do
+        return unless @circuits.key?(uri.origin) || @circuits.key?(uri.to_s)
 
-      circuit = get_circuit_for_uri(uri)
+        get_circuit_for_uri(uri)
+      end
 
       circuit.try_close
     end
@@ -32,7 +37,7 @@ module HTTPX::Plugins::CircuitBreaker
     # if circuit is open, it'll respond with the stored response.
     # if not, nil.
     def try_respond(request)
-      circuit = get_circuit_for_uri(request.uri)
+      circuit = @circuits.synchronize { get_circuit_for_uri(request.uri) }
 
       circuit.respond
     end
@@ -40,9 +45,7 @@ module HTTPX::Plugins::CircuitBreaker
     private
 
     def get_circuit_for_uri(uri)
-      uri = URI(uri)
-
-      if @circuits.key?(uri.origin)
+      if uri.respond_to?(:origin) && @circuits.key?(uri.origin)
         @circuits[uri.origin]
       else
         @circuits[uri.to_s]
diff --git a/sig/httpx.rbs b/sig/httpx.rbs
index d1e84440..f8b61851 100644
--- a/sig/httpx.rbs
+++ b/sig/httpx.rbs
@@ -5,7 +5,8 @@ module HTTPX
 
   VERSION: String
 
-  type uri = URI::HTTP | URI::HTTPS | string
+  type http_uri = URI::HTTP | URI::HTTPS
+  type uri = http_uri | string
   type generic_uri = String | URI::Generic
 
   type verb = "OPTIONS" | "GET" | "HEAD" | "POST" | "PUT" | "DELETE" | "TRACE" | "CONNECT" |
diff --git a/sig/io/unix.rbs b/sig/io/unix.rbs
index 29d2466c..e6bb7c7d 100644
--- a/sig/io/unix.rbs
+++ b/sig/io/unix.rbs
@@ -5,6 +5,6 @@ module HTTPX
 
     alias host path
 
-    def initialize: (URI::HTTP | URI::HTTPS origin, Array[String]? addresses, options options) -> void
+    def initialize: (http_uri origin, Array[String]? addresses, options options) -> void
   end
 end
diff --git a/sig/plugins/circuit_breaker.rbs b/sig/plugins/circuit_breaker.rbs
index 86611b59..5ec91b3b 100644
--- a/sig/plugins/circuit_breaker.rbs
+++ b/sig/plugins/circuit_breaker.rbs
@@ -3,17 +3,17 @@ module HTTPX
     module CircuitBreaker
 
       class CircuitStore
-        @circuits: Hash[String, Circuit]
+        @circuits: Hash[String, Circuit] & Mutex_m
 
-        def try_open: (generic_uri uri, response response) -> response?
+        def try_open: (uri uri, response response) -> response?
 
         def try_respond: (Request request) -> response?
 
-        def try_close: (generic_uri uri) -> void
+        def try_close: (http_uri uri) -> void
 
         private
 
-        def get_circuit_for_uri: (generic_uri uri) -> Circuit
+        def get_circuit_for_uri: (uri uri) -> Circuit
 
         def initialize: (Options & _CircuitOptions options) -> void
       end
diff --git a/sig/plugins/proxy/ssh.rbs b/sig/plugins/proxy/ssh.rbs
index 5976a25c..b37c5ac4 100644
--- a/sig/plugins/proxy/ssh.rbs
+++ b/sig/plugins/proxy/ssh.rbs
@@ -7,7 +7,7 @@ module HTTPX
         module InstanceMethods
           private
 
-          def build_gateway_socket: (int, URI::HTTP | URI::HTTPS, Options) ->  _ToIO
+          def build_gateway_socket: (int, http_uri, Options) ->  _ToIO
         end
       end
     end
diff --git a/sig/plugins/response_cache.rbs b/sig/plugins/response_cache.rbs
index d0a048e5..860d0d46 100644
--- a/sig/plugins/response_cache.rbs
+++ b/sig/plugins/response_cache.rbs
@@ -2,9 +2,10 @@ module HTTPX
   module Plugins
     module ResponseCache
       CACHEABLE_VERBS: Array[verb]
+      CACHEABLE_STATUS_CODES: Array[Integer]
 
-      def self?.cacheable_request?: (Request request) -> bool
-      def self?.cacheable_response?: (response response) -> bool
+      def self?.cacheable_request?: (Request & RequestMethods request) -> bool
+      def self?.cacheable_response?: (::HTTPX::ErrorResponse | (Response & ResponseMethods) response) -> bool
       def self?.cached_response?: (response response) -> bool
 
       class Store
@@ -34,6 +35,8 @@ module HTTPX
       end
 
       module RequestMethods
+        @response_cache_key: String
+
         def response_cache_key: () -> String
       end
 
diff --git a/sig/request.rbs b/sig/request.rbs
index 19ceb876..3f0fc0b2 100644
--- a/sig/request.rbs
+++ b/sig/request.rbs
@@ -7,7 +7,7 @@ module HTTPX
     USER_AGENT: String
 
     attr_reader verb: verb
-    attr_reader uri: URI::HTTP | URI::HTTPS
+    attr_reader uri: http_uri
     attr_reader headers: Headers
     attr_reader body: Body
     attr_reader state: Symbol
diff --git a/test/support/ci/build.sh b/test/support/ci/build.sh
index 991224d8..0cd7b72f 100755
--- a/test/support/ci/build.sh
+++ b/test/support/ci/build.sh
@@ -65,7 +65,7 @@ if [[ "$RUBY_ENGINE" = "ruby" ]] && [[ ${RUBY_VERSION:0:1} = "3" ]] && [[ ! $RUB
   export RUBYOPT="$RUBYOPT -rbundler/setup -rrbs/test/setup"
   export RBS_TEST_RAISE=true
   export RBS_TEST_LOGLEVEL=error
-  export RBS_TEST_OPT="-Isig -rset -rmutex_m -rforwardable -ruri -rjson -ripaddr -rpathname -rtime -rtimeout -rresolv -rsocket -ropenssl -rbase64 -rzlib -rcgi -rhttp-2-next"
+  export RBS_TEST_OPT="-Isig -rset -rmutex_m -rforwardable -ruri -rjson -ripaddr -rpathname -rtime -rtimeout -rresolv -rsocket -ropenssl -rbase64 -rzlib -rcgi -rdigest -rhttp-2-next"
   export RBS_TEST_TARGET="HTTP*"
 fi