diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 2827b7d..b0404fb 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -20,6 +20,11 @@
 All submissions, including submissions by project members, require review. We
 use Github pull requests for this purpose.
 
+### Breaking code changes
+When a breaking change is added, CI/CD will fail. If the change is expected,
+add a BREAKING_CHANGE_ACCEPTABLE=<reason> line to the CL description. This will
+cause CI/CD to skip checking breaking changes.
+
 ### The small print
 Contributions made by corporations are covered by a different agreement than
 the one above, the
diff --git a/go.mod b/go.mod
index dc69a07..ad59fde 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,11 @@
 module github.com/googleapis/gax-go
 
 require (
+	github.com/golang/protobuf v1.2.0
 	github.com/googleapis/gax-go/v2 v2.0.2
-	google.golang.org/grpc v1.16.0
+	golang.org/x/exp v0.0.0-20190221220918-438050ddec5e
+	golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3
+	golang.org/x/tools v0.0.0-20190114222345-bf090417da8b
+	google.golang.org/grpc v1.19.0
+	honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099
 )
diff --git a/go.sum b/go.sum
index 2fb5cc0..2c11f2f 100644
--- a/go.sum
+++ b/go.sum
@@ -1,4 +1,6 @@
 cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
+github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
+github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b h1:VKtxabqXZkF25pY9ekfRL6a582T4P37/31XEstQ5p58=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
@@ -8,8 +10,14 @@
 github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/googleapis/gax-go/v2 v2.0.2 h1:/rNgUniLy2vDXiK2xyJOcirGpC3G99dtK1NWx26WZ8Y=
 github.com/googleapis/gax-go/v2 v2.0.2/go.mod h1:LLvjysVCY1JZeum8Z6l8qUty8fiNwE08qbEPm1M08qg=
+github.com/kisielk/gotool v1.0.0 h1:AV2c/EiW3KqPNT9ZKl07ehoAGi4C5/01Cfbblndcapg=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
+golang.org/x/exp v0.0.0-20190221220918-438050ddec5e h1:dVreTP5bOOWt5GFwwvgTE2iU0TkIqi2x3r0b8qGlp6k=
+golang.org/x/exp v0.0.0-20190221220918-438050ddec5e/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
+golang.org/x/lint v0.0.0-20180702182130-06c8688daad7 h1:00BeQWmeaGazuOrq8Q5K5d3/cHaGuFrZzpaHBXfrsUA=
 golang.org/x/lint v0.0.0-20180702182130-06c8688daad7/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
+golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3 h1:x/bBzNauLQAlE3fLku/xy92Y8QwKX5HZymrMz2IiKFc=
+golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d h1:g9qWBGx4puODJTMVyoPrpoxPFgVGd+z1DZwjfRu4d0I=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
@@ -19,10 +27,18 @@
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20180828015842-6cd1fcedba52 h1:JG/0uqcGdTNgq7FdU+61l5Pdmb8putNZlXb65bJBROs=
 golang.org/x/tools v0.0.0-20180828015842-6cd1fcedba52/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/tools v0.0.0-20190114222345-bf090417da8b h1:qMK98NmNCRVDIYFycQ5yVRkvgDUFfdP8Ip4KqmDEB7g=
+golang.org/x/tools v0.0.0-20190114222345-bf090417da8b/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 google.golang.org/appengine v1.1.0/go.mod h1:EbEs0AVv82hx2wNQdGPgUI5lhzA/G0D9YwlJXL52JkM=
 google.golang.org/genproto v0.0.0-20180817151627-c66870c02cf8 h1:Nw54tB0rB7hY/N0NQvRW8DG4Yk3Q6T9cu9RcFQDu1tc=
 google.golang.org/genproto v0.0.0-20180817151627-c66870c02cf8/go.mod h1:JiN7NxoALGmiZfu7CAH4rXhgtRTLTxftemlI0sWmxmc=
 google.golang.org/grpc v1.16.0 h1:dz5IJGuC2BB7qXR5AyHNwAUBhZscK2xVez7mznh72sY=
 google.golang.org/grpc v1.16.0/go.mod h1:0JHn/cJsOMiMfNA9+DeHDlAU7KAAB5GDlYFpa9MZMio=
+google.golang.org/grpc v1.19.0 h1:cfg4PD8YEdSFnm7qLV4++93WcmhH2nIUhMjhdCvl3j8=
+google.golang.org/grpc v1.19.0/go.mod h1:mqu4LbDTu4XGKhr4mRzUsmM4RtVoemTSY81AxZiDr8c=
+honnef.co/go/tools v0.0.0-20180728063816-88497007e858 h1:wN+eVZ7U+gqdqkec6C6VXR1OFf9a5Ul9ETzeYsYv20g=
 honnef.co/go/tools v0.0.0-20180728063816-88497007e858/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
+honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099 h1:XJP7lxbSxWLOMNdBE4B/STaqVy6L73o0knwj2vIlxnw=
+honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
diff --git a/internal/kokoro/check_incompat_changes.sh b/internal/kokoro/check_incompat_changes.sh
index 68c0f9f..9236b97 100755
--- a/internal/kokoro/check_incompat_changes.sh
+++ b/internal/kokoro/check_incompat_changes.sh
@@ -3,16 +3,20 @@
 # Display commands being run
 set -x
 
-# Only run apidiff checks on go1.11 (we only need it once).
+# Only run apidiff checks on go1.12 (we only need it once).
 # TODO(deklerk) We should pass an environment variable from kokoro to decide
 # this logic instead.
-if [[ `go version` != *"go1.11"* ]]; then
+if [[ `go version` != *"go1.12"* ]]; then
     exit 0
 fi
 
-try3() { eval "$*" || eval "$*" || eval "$*"; }
+if git log -1 | grep BREAKING_CHANGE_ACCEPTABLE; then
+  exit 0
+fi
 
-try3 go get -u golang.org/x/exp/cmd/apidiff
+export GO111MODULE=on
+
+go install golang.org/x/exp/cmd/apidiff
 
 # We compare against master@HEAD. This is unfortunate in some cases: if you're
 # working on an out-of-date branch, and master gets some new feature (that has
diff --git a/internal/kokoro/test.sh b/internal/kokoro/test.sh
index 40f6edd..d213839 100755
--- a/internal/kokoro/test.sh
+++ b/internal/kokoro/test.sh
@@ -15,7 +15,7 @@
 
 # Set $GOPATH
 export GOPATH="$HOME/go"
-export GAX_HOME=$GOPATH/src/googleapis/gax-go
+export GAX_HOME=$GOPATH/src/github.com/googleapis/gax-go
 export PATH="$GOPATH/bin:$PATH"
 mkdir -p $GAX_HOME
 
@@ -24,10 +24,24 @@
 cd $GAX_HOME
 
 try3() { eval "$*" || eval "$*" || eval "$*"; }
-try3 go get -v -t ./...
 
-./internal/kokoro/vet.sh
+download_deps() {
+    if [[ `go version` == *"go1.11"* ]] || [[ `go version` == *"go1.12"* ]]; then
+        export GO111MODULE=on
+        # All packages, including +build tools, are fetched.
+        try3 go mod download
+    else
+        # Because we don't provide -tags tools, the +build tools
+        # dependencies aren't fetched.
+        try3 go get -v -t ./...
+    fi
+}
+
+download_deps
 ./internal/kokoro/check_incompat_changes.sh
+./internal/kokoro/vet.sh
+go test -race -v . 2>&1 | tee $KOKORO_ARTIFACTS_DIR/$KOKORO_GERRIT_CHANGE_NUMBER.txt
 
-# Run tests and tee output to log file, to be pushed to GCS as artifact.
-go test -race -v ./... 2>&1 | tee $KOKORO_ARTIFACTS_DIR/$KOKORO_GERRIT_CHANGE_NUMBER.txt
+cd v2
+download_deps
+go test -race -v . 2>&1 | tee $KOKORO_ARTIFACTS_DIR/$KOKORO_GERRIT_CHANGE_NUMBER.txt
diff --git a/internal/kokoro/vet.sh b/internal/kokoro/vet.sh
index 9fcbed9..f15de65 100755
--- a/internal/kokoro/vet.sh
+++ b/internal/kokoro/vet.sh
@@ -8,25 +8,28 @@
 
 # Only run the linter on go1.11, since it needs type aliases (and we only care about its output once).
 # TODO(deklerk) We should pass an environment variable from kokoro to decide this logic instead.
-if [[ `go version` != *"go1.11"* ]]; then
+if [[ `go version` != *"go1.12"* ]]; then
     exit 0
 fi
 
-pwd
+export GO111MODULE=on
 
-# Fail if a dependency was added without the necessary go.mod/go.sum change
-# being part of the commit.
-GO111MODULE=on go mod tidy
-git diff go.mod | tee /dev/stderr | (! read)
-git diff go.sum | tee /dev/stderr | (! read)
-
-try3() { eval "$*" || eval "$*" || eval "$*"; }
-
-try3 go get -u \
+go install \
+  github.com/golang/protobuf/proto \
+  github.com/golang/protobuf/protoc-gen-go \
   golang.org/x/lint/golint \
   golang.org/x/tools/cmd/goimports \
   honnef.co/go/tools/cmd/staticcheck
 
+# Fail if a dependency was added without the necessary go.mod/go.sum change
+# being part of the commit.
+go mod tidy
+git diff go.mod | tee /dev/stderr | (! read)
+git diff go.sum | tee /dev/stderr | (! read)
+
+# Easier to debug CI.
+pwd
+
 # Look at all .go files (ignoring .pb.go files) and make sure they have a Copyright. Fail if any don't.
 git ls-files "*[^.pb].go" | xargs grep -L "\(Copyright [0-9]\{4,\}\)" 2>&1 | tee /dev/stderr | (! read)
 gofmt -s -d -l . 2>&1 | tee /dev/stderr | (! read)
diff --git a/tools.go b/tools.go
new file mode 100644
index 0000000..ffb3ad4
--- /dev/null
+++ b/tools.go
@@ -0,0 +1,33 @@
+// +build tools
+
+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This package exists to cause `go mod` and `go get` to believe these tools
+// are dependencies, even though they are not runtime dependencies of any
+// package (these are tools used by our CI builds). This means they will appear
+// in our `go.mod` file, but will not be a part of the build. Also, since the
+// build target is something non-existent, these should not be included in any
+// binaries.
+
+package gax
+
+import (
+	_ "github.com/golang/protobuf/proto"
+	_ "github.com/golang/protobuf/protoc-gen-go"
+	_ "golang.org/x/exp/cmd/apidiff"
+	_ "golang.org/x/lint/golint"
+	_ "golang.org/x/tools/cmd/goimports"
+	_ "honnef.co/go/tools/cmd/staticcheck"
+)
diff --git a/v2/go.mod b/v2/go.mod
index c88c205..0c91100 100644
--- a/v2/go.mod
+++ b/v2/go.mod
@@ -1,3 +1,5 @@
 module github.com/googleapis/gax-go/v2
 
-require google.golang.org/grpc v1.16.0
+go 1.12
+
+require google.golang.org/grpc v1.19.0
diff --git a/v2/go.sum b/v2/go.sum
index bad34ab..7fa23ec 100644
--- a/v2/go.sum
+++ b/v2/go.sum
@@ -1,13 +1,12 @@
 cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
+github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b h1:VKtxabqXZkF25pY9ekfRL6a582T4P37/31XEstQ5p58=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
-github.com/golang/lint v0.0.0-20180702182130-06c8688daad7/go.mod h1:tluoj9z5200jBnyusfRPU2LqT6J+DAorxEvtC7LHB+E=
 github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
 github.com/golang/protobuf v1.2.0 h1:P3YflyNX/ehuJFLhxviNdFxQPkGK5cDcApsge1SqnvM=
 github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
-github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
-golang.org/x/lint v0.0.0-20180702182130-06c8688daad7/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
+golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d h1:g9qWBGx4puODJTMVyoPrpoxPFgVGd+z1DZwjfRu4d0I=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
@@ -17,10 +16,10 @@
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
-golang.org/x/tools v0.0.0-20180828015842-6cd1fcedba52/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/tools v0.0.0-20190114222345-bf090417da8b/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 google.golang.org/appengine v1.1.0/go.mod h1:EbEs0AVv82hx2wNQdGPgUI5lhzA/G0D9YwlJXL52JkM=
 google.golang.org/genproto v0.0.0-20180817151627-c66870c02cf8 h1:Nw54tB0rB7hY/N0NQvRW8DG4Yk3Q6T9cu9RcFQDu1tc=
 google.golang.org/genproto v0.0.0-20180817151627-c66870c02cf8/go.mod h1:JiN7NxoALGmiZfu7CAH4rXhgtRTLTxftemlI0sWmxmc=
-google.golang.org/grpc v1.16.0 h1:dz5IJGuC2BB7qXR5AyHNwAUBhZscK2xVez7mznh72sY=
-google.golang.org/grpc v1.16.0/go.mod h1:0JHn/cJsOMiMfNA9+DeHDlAU7KAAB5GDlYFpa9MZMio=
-honnef.co/go/tools v0.0.0-20180728063816-88497007e858/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
+google.golang.org/grpc v1.19.0 h1:cfg4PD8YEdSFnm7qLV4++93WcmhH2nIUhMjhdCvl3j8=
+google.golang.org/grpc v1.19.0/go.mod h1:mqu4LbDTu4XGKhr4mRzUsmM4RtVoemTSY81AxZiDr8c=
+honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=