diff --git a/armadillo_azure-pipelines.yml b/armadillo_azure-pipelines.yml
index 2fba0a0a..d0a7d096 100644
--- a/armadillo_azure-pipelines.yml
+++ b/armadillo_azure-pipelines.yml
@@ -122,6 +122,18 @@ jobs:
     condition: succeeded()
 
 
+    #####################################################################################
+    # Restore the R package library from a previous run. Combined with the
+    # "install only missing packages" logic in the next step, a cache hit makes
+    # dependency installation near-instant. Bump the 'v1' token to rebuild the cache
+    # (e.g. when the package list below changes).
+  - task: Cache@2
+    inputs:
+      key: 'rpkgs | "$(Agent.OS)" | v1'
+      path: '/usr/local/lib/R/site-library'
+    displayName: 'Restore cached R packages'
+
+
     #####################################################################################
     # Install R and all the dependencies dsBaseClient requires.
     # If previous steps have failed then don't run.
@@ -134,11 +146,13 @@ jobs:
 
       sudo apt-get install -qq libxml2-dev libcurl4-openssl-dev libssl-dev libgsl-dev libgit2-dev r-base -y
       sudo apt-get install -qq libharfbuzz-dev libfribidi-dev libmagick++-dev libudunits2-dev libuv1-dev -y
-      sudo R -q -e "install.packages(c('devtools','covr'), dependencies=TRUE, repos='https://cloud.r-project.org')"
-      sudo R -q -e "install.packages(c('fields','meta','metafor','ggplot2','gridExtra','data.table'), dependencies=TRUE, repos='https://cloud.r-project.org')"
-      sudo R -q -e "install.packages(c('DSI','DSOpal','DSLite'), dependencies=TRUE, repos='https://cloud.r-project.org')"
-      sudo R -q -e "install.packages(c('MolgenisAuth', 'MolgenisArmadillo', 'DSMolgenisArmadillo'), dependencies=TRUE, repos='https://cloud.r-project.org')"
-      sudo R -q -e "install.packages(c('DescTools','e1071'), dependencies=TRUE, repos='https://cloud.r-project.org')"
+
+      # Use Posit Public Package Manager, which serves precompiled binary packages
+      # for this Ubuntu release instead of source - so dependencies are downloaded
+      # rather than compiled (the slow part). The HTTPUserAgent option is what makes
+      # the manager hand back binaries. The setdiff() only installs packages not
+      # already present, so a restored (cached) site-library is reused.
+      sudo R -q -e "options(repos=c(CRAN=paste0('https://packagemanager.posit.co/cran/__linux__/', system('lsb_release -cs', intern=TRUE), '/latest')), HTTPUserAgent=sprintf('R/%s R (%s)', getRversion(), paste(getRversion(), R.version\$platform, R.version\$arch, R.version\$os)), Ncpus=4); pkgs <- c('devtools','covr','fields','meta','metafor','ggplot2','gridExtra','data.table','DSI','DSOpal','DSLite','MolgenisAuth','MolgenisArmadillo','DSMolgenisArmadillo','DescTools','e1071'); to_install <- setdiff(pkgs, rownames(installed.packages())); if (length(to_install)) install.packages(to_install, dependencies=TRUE)"
 
       sudo R -q -e "library('devtools'); devtools::install_github(repo='datashield/dsDangerClient', ref='v6.3.4-dev', dependencies = TRUE)"
 
diff --git a/opal_azure-pipelines.yml b/opal_azure-pipelines.yml
index 3844edeb..941fa7a8 100644
--- a/opal_azure-pipelines.yml
+++ b/opal_azure-pipelines.yml
@@ -103,6 +103,18 @@ jobs:
     condition: succeeded()
 
 
+    #####################################################################################
+    # Restore the R package library from a previous run. Combined with the
+    # "install only missing packages" logic in the next step, a cache hit makes
+    # dependency installation near-instant. Bump the 'v1' token to rebuild the cache
+    # (e.g. when the package list below changes).
+  - task: Cache@2
+    inputs:
+      key: 'rpkgs | "$(Agent.OS)" | opal | v1'
+      path: '/usr/local/lib/R/site-library'
+    displayName: 'Restore cached R packages'
+
+
     #####################################################################################
     # Install R and all the dependencies dsBaseClient requires.
     # If previous steps have failed then don't run.
@@ -115,12 +127,13 @@ jobs:
 
       sudo apt-get install -qq libxml2-dev libcurl4-openssl-dev libssl-dev libgsl-dev libgit2-dev r-base -y
       sudo apt-get install -qq libharfbuzz-dev libfribidi-dev libmagick++-dev libudunits2-dev libuv1-dev -y
-      sudo R -q -e "install.packages(c('curl','httr'), dependencies=TRUE, repos='https://cloud.r-project.org')"
-      sudo R -q -e "install.packages(c('devtools','covr'), dependencies=TRUE, repos='https://cloud.r-project.org')"
-      sudo R -q -e "install.packages(c('fields','meta','metafor','ggplot2','gridExtra','data.table'), dependencies=TRUE, repos='https://cloud.r-project.org')"
-      sudo R -q -e "install.packages(c('DSI','DSOpal','DSLite'), dependencies=TRUE, repos='https://cloud.r-project.org')"
-      sudo R -q -e "install.packages(c('MolgenisAuth', 'MolgenisArmadillo', 'DSMolgenisArmadillo'), dependencies=TRUE, repos='https://cloud.r-project.org')"
-      sudo R -q -e "install.packages(c('DescTools','e1071'), dependencies=TRUE, repos='https://cloud.r-project.org')"
+
+      # Use Posit Public Package Manager, which serves precompiled binary packages
+      # for this Ubuntu release instead of source - so dependencies are downloaded
+      # rather than compiled (the slow part). The HTTPUserAgent option is what makes
+      # the manager hand back binaries. The setdiff() only installs packages not
+      # already present, so a restored (cached) site-library is reused.
+      sudo R -q -e "options(repos=c(CRAN=paste0('https://packagemanager.posit.co/cran/__linux__/', system('lsb_release -cs', intern=TRUE), '/latest')), HTTPUserAgent=sprintf('R/%s R (%s)', getRversion(), paste(getRversion(), R.version\$platform, R.version\$arch, R.version\$os)), Ncpus=4); pkgs <- c('curl','httr','devtools','covr','fields','meta','metafor','ggplot2','gridExtra','data.table','DSI','DSOpal','DSLite','MolgenisAuth','MolgenisArmadillo','DSMolgenisArmadillo','DescTools','e1071'); to_install <- setdiff(pkgs, rownames(installed.packages())); if (length(to_install)) install.packages(to_install, dependencies=TRUE)"
 
       sudo R -q -e "library('devtools'); devtools::install_github(repo='datashield/dsDangerClient', ref='6.3.4', dependencies = TRUE)"