diff --git a/.github/workflows/R-CMD-check.yaml b/.github/workflows/R-CMD-check.yaml
index 6664d79f..aeedc01d 100644
--- a/.github/workflows/R-CMD-check.yaml
+++ b/.github/workflows/R-CMD-check.yaml
@@ -11,6 +11,12 @@ name: Unit tests
   pull_request:
     branches:
       - master
+  workflow_dispatch:
+    inputs:
+      tarball_url:
+        description: 'CmdStan tarball URL to test with.'
+        required: false
+        default: ''
 
 jobs:
   R-CMD-check:
@@ -36,6 +42,7 @@ jobs:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
       NOT_CRAN: true
       CMDSTANR_OPENCL_TESTS: ${{ matrix.config.opencl }}
+      CMDSTAN_TEST_TARBALL_URL: ${{ github.event.inputs.tarball_url }}
       PKG_SYSREQS_DB_UPDATE_TIMEOUT: 30s
 
     steps:
@@ -86,7 +93,16 @@ jobs:
       - name: Install cmdstan
         run: |
           cmdstanr::check_cmdstan_toolchain(fix = TRUE)
-          cmdstanr::install_cmdstan(cores = 2)
+          tarball_url <- Sys.getenv("CMDSTAN_TEST_TARBALL_URL")
+          if (nzchar(tarball_url)) {
+            cmdstanr::install_cmdstan(
+              cores = 2,
+              overwrite = TRUE,
+              release_url = tarball_url
+            )
+          } else {
+            cmdstanr::install_cmdstan(cores = 2)
+          }
         shell: Rscript {0}
 
       - name: Session info
diff --git a/.github/workflows/cmdstan-tarball-check.yaml b/.github/workflows/cmdstan-tarball-check.yaml
deleted file mode 100644
index 056e37f6..00000000
--- a/.github/workflows/cmdstan-tarball-check.yaml
+++ /dev/null
@@ -1,101 +0,0 @@
----
-# Github Actions workflow to check CmdStanR tarball
-# yamllint disable rule:line-length
-
-name: Custom CmdStan tarball unit tests
-
-'on':
-  workflow_dispatch:
-    inputs:
-      tarball_url:
-        description: 'CmdStan tarball URL to test with.'
-        required: true
-        default: 'latest'
-
-jobs:
-  tarball-check:
-    runs-on: ${{ matrix.config.os }}
-
-    name: ${{ matrix.config.os }} (${{ matrix.config.r }})
-
-    strategy:
-      fail-fast: false
-      matrix:
-        config:
-          - {os: macOS-latest, r: 'release', rtools: ''}
-          - {os: windows-latest, r: 'release', rtools: '44'}
-          - {os: ubuntu-20.04, r: 'release', rtools: ''}
-    env:
-      R_REMOTES_NO_ERRORS_FROM_WARNINGS: true
-      GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
-      CMDSTAN_TEST_TARBALL_URL: ${{ github.event.inputs.tarball_url }}
-      NOT_CRAN: true
-
-    steps:
-      - uses: actions/checkout@v6
-      - name: Install system dependencies
-        if: runner.os == 'Linux'
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y libcurl4-openssl-dev || true
-          sudo apt-get install -y openmpi-bin openmpi-common libopenmpi-dev || true
-
-      - uses: r-lib/actions/setup-r@v2.11.3
-        with:
-          r-version: ${{ matrix.config.r }}
-          rtools-version: ${{ matrix.config.rtools }}
-
-      - uses: r-lib/actions/setup-pandoc@v2.11.3
-
-      - name: Query dependencies
-        run: |
-          install.packages('remotes')
-          saveRDS(remotes::dev_package_deps(dependencies = TRUE), ".github/depends.Rds", version = 2)
-          writeLines(sprintf("R-%i.%i", getRversion()$major, getRversion()$minor), ".github/R-version")
-        shell: Rscript {0}
-
-      - name: Cache R packages
-        if: runner.os != 'Windows'
-        uses: actions/cache@v5
-        with:
-          path: ${{ env.R_LIBS_USER }}
-          key: ${{ runner.os }}-${{ hashFiles('.github/R-version') }}-1-${{ hashFiles('.github/depends.Rds') }}
-          restore-keys: ${{ runner.os }}-${{ hashFiles('.github/R-version') }}-1-
-
-      - name: Install dependencies
-        run: |
-          remotes::install_deps(dependencies = TRUE)
-          remotes::install_cran("rcmdcheck")
-          remotes::install_local(path = ".", INSTALL_opts = "--no-test-load")
-          cmdstanr::check_cmdstan_toolchain(fix = TRUE)
-          if (Sys.getenv("CMDSTAN_TEST_TARBALL_URL") == "latest") {
-            cmdstanr::install_cmdstan(cores = 2, overwrite = TRUE)
-          } else {
-            cmdstanr::install_cmdstan(cores = 2, overwrite = TRUE, release_url = "${{ github.event.inputs.tarball_url }}")
-          }
-        shell: Rscript {0}
-
-      - name: Session info
-        run: |
-          options(width = 100)
-          pkgs <- installed.packages()[, "Package"]
-          sessioninfo::session_info(pkgs, include_base = TRUE)
-        shell: Rscript {0}
-
-      - name: Check
-        env:
-          _R_CHECK_CRAN_INCOMING_: false
-        run: rcmdcheck::rcmdcheck(args = c("--no-manual", "--as-cran", "--ignore-vignettes"), build_args = c("--no-build-vignettes"), error_on = "warning", check_dir = "check")
-        shell: Rscript {0}
-
-      - name: Show testthat output
-        if: always()
-        run: find check -name 'testthat.Rout*' -exec cat '{}' \; || true
-        shell: bash
-
-      - name: Upload check results
-        if: failure()
-        uses: actions/upload-artifact@v6
-        with:
-          name: ${{ runner.os }}-r${{ matrix.config.r }}-results
-          path: check
diff --git a/tests/testthat/test-install.R b/tests/testthat/test-install.R
index a9c06482..ad7ad069 100644
--- a/tests/testthat/test-install.R
+++ b/tests/testthat/test-install.R
@@ -1,5 +1,8 @@
 context("install")
 
+# avoid parallel on Mac due to strange intermittent TBB errors on Github Actions
+CORES <- if (os_is_macos()) 1 else 2
+
 cmdstan_test_tarball_url <- Sys.getenv("CMDSTAN_TEST_TARBALL_URL")
 if (!nzchar(cmdstan_test_tarball_url)) {
   cmdstan_test_tarball_url <- NULL
@@ -13,7 +16,7 @@ test_that("install_cmdstan() successfully installs cmdstan", {
   }
   expect_message(
     expect_output(
-      install_cmdstan(dir = dir, cores = 2, quiet = FALSE, overwrite = TRUE,
+      install_cmdstan(dir = dir, cores = CORES, quiet = FALSE, overwrite = TRUE,
                       release_url = cmdstan_test_tarball_url,
                       wsl = os_is_wsl()),
       "Compiling C++ code",
@@ -52,7 +55,7 @@ test_that("install_cmdstan() errors if it times out", {
   expect_warning(
     expect_message(
       install_cmdstan(dir = dir, timeout = 1, quiet = TRUE, overwrite = dir_exists,
-                      release_url = cmdstan_test_tarball_url, wsl = os_is_wsl()),
+                      cores = CORES, wsl = os_is_wsl()),
       if (dir_exists) "* Removing the existing installation" else "* * Installing CmdStan from https://github.com",
       fixed = TRUE
     ),
@@ -64,8 +67,7 @@ test_that("install_cmdstan() errors if it times out", {
   expect_warning(
     expect_message(
       install_cmdstan(dir = dir, timeout = 1, quiet = FALSE, overwrite = dir_exists,
-                      release_url = cmdstan_test_tarball_url,
-                      wsl = os_is_wsl()),
+                      cores = CORES, wsl = os_is_wsl()),
       if (dir_exists) "* Removing the existing installation" else "* * Installing CmdStan from https://github.com",
       fixed = TRUE
     ),
@@ -91,6 +93,9 @@ test_that("install_cmdstan() errors if invalid version or URL", {
 })
 
 test_that("install_cmdstan() works with version and release_url", {
+  # this test is irrelevant if tests are using a release candidate tarball URL so skip
+  skip_if(!is.null(cmdstan_test_tarball_url))
+
   if (getRversion() < '3.5.0') {
     dir <- tempdir()
   } else {
@@ -99,8 +104,8 @@ test_that("install_cmdstan() works with version and release_url", {
 
   expect_message(
     expect_output(
-      install_cmdstan(dir = dir, overwrite = TRUE, cores = 4,
-                      release_url = "https://github.com/stan-dev/cmdstan/releases/download/v2.35.0/cmdstan-2.35.0.tar.gz",
+      install_cmdstan(dir = dir, overwrite = TRUE, cores = CORES,
+                      release_url = "https://github.com/stan-dev/cmdstan/releases/download/v2.36.0/cmdstan-2.36.0.tar.gz",
                       wsl = os_is_wsl()),
       "Compiling C++ code",
       fixed = TRUE
@@ -111,8 +116,8 @@ test_that("install_cmdstan() works with version and release_url", {
   expect_warning(
     expect_message(
       expect_output(
-        install_cmdstan(dir = dir, overwrite = TRUE, cores = 4,
-                        version = "2.35.0",
+        install_cmdstan(dir = dir, overwrite = TRUE, cores = CORES,
+                        version = "2.36.0",
                         # the URL is intentionally invalid to test that the version has higher priority
                         release_url = "https://github.com/stan-dev/cmdstan/releases/download/v2.27.3/cmdstan-2.27.3.tar.gz",
                         wsl = os_is_wsl()),
@@ -125,7 +130,7 @@ test_that("install_cmdstan() works with version and release_url", {
     "version and release_url shouldn't both be specified",
     fixed = TRUE
   )
-  expect_true(dir.exists(file.path(dir, "cmdstan-2.35.0")))
+  expect_true(dir.exists(file.path(dir, "cmdstan-2.36.0")))
   set_cmdstan_path(cmdstan_default_path())
 })
 
@@ -187,7 +192,7 @@ test_that("toolchain checks on Windows with RTools 3.5 work", {
 
 test_that("clean and rebuild works", {
   expect_output(
-    rebuild_cmdstan(),
+    rebuild_cmdstan(cores = CORES),
     paste0("CmdStan v", cmdstan_version(), " built"),
     fixed = TRUE
   )
@@ -215,11 +220,11 @@ test_that("Downloads respect quiet argument", {
   # expect_message has trouble capturing the messages from download.file
   # so handle manually
   install_normal <- suppressWarnings(
-    capture.output(install_cmdstan(dir = dir, overwrite = TRUE, quiet = FALSE),
+    capture.output(install_cmdstan(dir = dir, overwrite = TRUE, quiet = FALSE, cores = CORES),
                    type = "message")
   )
   install_quiet <- suppressWarnings(
-    capture.output(install_cmdstan(dir = dir, overwrite = TRUE, quiet = TRUE),
+    capture.output(install_cmdstan(dir = dir, overwrite = TRUE, quiet = TRUE, cores = CORES),
                    type = "message")
   )
 
@@ -256,15 +261,15 @@ test_that("Install from release file works", {
     dir <- tempdir(check = TRUE)
   }
 
-  destfile = file.path(dir, "cmdstan-2.35.0.tar.gz")
+  destfile <- file.path(dir, "cmdstan-2.36.0.tar.gz")
 
   download_with_retries(
-    "https://github.com/stan-dev/cmdstan/releases/download/v2.35.0/cmdstan-2.35.0.tar.gz",
+    "https://github.com/stan-dev/cmdstan/releases/download/v2.36.0/cmdstan-2.36.0.tar.gz",
     destfile)
 
   expect_message(
     expect_output(
-      install_cmdstan(dir = dir, cores = 2, quiet = FALSE, overwrite = TRUE,
+      install_cmdstan(dir = dir, cores = CORES, quiet = FALSE, overwrite = TRUE,
                       release_file = destfile,
                       wsl = os_is_wsl()),
       "Compiling C++ code",