diff --git a/.github/scripts/deployment-environment.sh b/.github/scripts/deployment-environment.sh
index 79d173324..26d6f648d 100644
--- a/.github/scripts/deployment-environment.sh
+++ b/.github/scripts/deployment-environment.sh
@@ -1,12 +1,12 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-# Pages selects production by branch. Manual previews of master must use a
-# preview alias, while a manual production deploy must explicitly target master.
-if [[ "${GITHUB_EVENT_NAME:-}" == "push" && "$RAW_BRANCH" == "master" ]] ||
+# Keep the Pages production branch aligned with the repository's default branch.
+# Manual previews of that branch still use an isolated preview alias.
+if [[ "${GITHUB_EVENT_NAME:-}" == "push" && "$RAW_BRANCH" == "$PRODUCTION_BRANCH" ]] ||
    [[ "${GITHUB_EVENT_NAME:-}" == "workflow_dispatch" && "${DEPLOY_ENVIRONMENT:-}" == "production" ]]; then
   {
-    echo "SAFE_BRANCH=master"
+    echo "SAFE_BRANCH=$PRODUCTION_BRANCH"
     echo "DOCS_DEPLOYMENT_ENVIRONMENT=production"
     echo "VITE_DEPLOYMENT_URL="
     echo "DOCS_DEPLOYMENT_URL=https://rescript-lang.org"
diff --git a/.github/scripts/lighthouse-environment.sh b/.github/scripts/lighthouse-environment.sh
index 701c1d9c2..385b31527 100644
--- a/.github/scripts/lighthouse-environment.sh
+++ b/.github/scripts/lighthouse-environment.sh
@@ -13,8 +13,8 @@ else
   TARGET_ENVIRONMENT="${DOCS_DEPLOYMENT_ENVIRONMENT:-}"
 fi
 
-ARTIFACT_NAME=$(node "$REPOSITORY_ROOT/apps/docs/scripts/lighthouse-report.mjs" artifact-name "$RAW_BRANCH" "${DOCS_DEPLOYMENT_ENVIRONMENT:-}")
-TARGET_ARTIFACT_NAME=$(node "$REPOSITORY_ROOT/apps/docs/scripts/lighthouse-report.mjs" artifact-name "$RAW_TARGET_BRANCH" "$TARGET_ENVIRONMENT")
+ARTIFACT_NAME=$(node "$REPOSITORY_ROOT/apps/docs/scripts/lighthouse-report.mjs" artifact-name "$RAW_BRANCH" "${DOCS_DEPLOYMENT_ENVIRONMENT:-}" "$PRODUCTION_BRANCH")
+TARGET_ARTIFACT_NAME=$(node "$REPOSITORY_ROOT/apps/docs/scripts/lighthouse-report.mjs" artifact-name "$RAW_TARGET_BRANCH" "$TARGET_ENVIRONMENT" "$PRODUCTION_BRANCH")
 
 {
   echo "LIGHTHOUSE_ARTIFACT_NAME=$ARTIFACT_NAME"
diff --git a/.github/workflows/deploy.yml b/.github/workflows/deploy.yml
index 7a647d212..95410d137 100644
--- a/.github/workflows/deploy.yml
+++ b/.github/workflows/deploy.yml
@@ -3,6 +3,7 @@ on:
   push:
     branches:
       - master
+      - v12
   workflow_dispatch:
     inputs:
       environment:
@@ -15,6 +16,9 @@ on:
         default: "preview"
   pull_request:
 
+env:
+  PRODUCTION_BRANCH: ${{ github.event.repository.default_branch }}
+
 jobs:
   deploy:
     runs-on: ubuntu-24.04
@@ -180,7 +184,7 @@ jobs:
           SAFE_BRANCH=$(echo "$RAW_BRANCH" | tr '[:upper:]' '[:lower:]' | sed -E 's/[^a-z0-9-]+/-/g; s/^-+//; s/-+$//; s/-+/-/g')
           SAFE_BRANCH="${SAFE_BRANCH:0:28}"
 
-          if [[ "${{ github.event_name }}" == "push" && "$RAW_BRANCH" == "master" ]] || [[ "${{ inputs.environment }}" == "production" ]]; then
+          if [[ "${{ github.event_name }}" == "push" && "$RAW_BRANCH" == "$PRODUCTION_BRANCH" ]] || [[ "${{ inputs.environment }}" == "production" ]]; then
             echo "GUIDE_DEPLOY_COMMAND=deploy" >> "$GITHUB_ENV"
             echo "GUIDE_DEPLOYMENT_ENVIRONMENT=guide-production" >> "$GITHUB_ENV"
             echo "GUIDE_PRODUCTION_ENVIRONMENT=true" >> "$GITHUB_ENV"
diff --git a/README.md b/README.md
index bd4578c9e..34a8e1e32 100644
--- a/README.md
+++ b/README.md
@@ -177,7 +177,7 @@ yarn ci:test
 For a headless run of a single suite, use `yarn vitest --browser.headless --run`
 for docs or `yarn vitest:guide --browser.headless --run` for the guide.
 
-Visual screenshot baselines are generated in CI's pinned Linux browser environment. Local snapshot updates are blocked. Push your feature branch, then open [Update Visual Regression Screenshots](https://github.com/rescript-lang/rescript-lang.org/actions/workflows/update-visual-screenshots.yml), select that branch, and choose **Run workflow**. The workflow refuses `master` and commits any changed PNGs back to the selected branch.
+Visual screenshot baselines are generated in CI's pinned Linux browser environment. Local snapshot updates are blocked. Push your feature branch, then open [Update Visual Regression Screenshots](https://github.com/rescript-lang/rescript-lang.org/actions/workflows/update-visual-screenshots.yml), select that branch, and choose **Run workflow**. The workflow refuses the default branch and commits any changed PNGs back to the selected branch.
 
 You can also dispatch the workflow with the GitHub CLI, replacing `<feature-branch>` with your pushed branch:
 
diff --git a/apps/docs/scripts/__tests__/LighthouseFixtures.res b/apps/docs/scripts/__tests__/LighthouseFixtures.res
index 4c2f194f4..6245d27d4 100644
--- a/apps/docs/scripts/__tests__/LighthouseFixtures.res
+++ b/apps/docs/scripts/__tests__/LighthouseFixtures.res
@@ -27,7 +27,8 @@ type commentInput = {
 }
 
 @module("../lighthouse-report.mjs")
-external artifactName: (string, ~environment: string=?) => string = "lighthouseArtifactName"
+external artifactName: (string, ~environment: string=?, ~productionBranch: string=?) => string =
+  "lighthouseArtifactName"
 @module("../lighthouse-report.mjs") external median: array<float> => float = "median"
 @module("../lighthouse-report.mjs")
 external createBaseline: baselineInput => baseline = "createBaseline"
diff --git a/apps/docs/scripts/__tests__/LighthouseReport_.test.res b/apps/docs/scripts/__tests__/LighthouseReport_.test.res
index 1ef51a79b..3b30f450f 100644
--- a/apps/docs/scripts/__tests__/LighthouseReport_.test.res
+++ b/apps/docs/scripts/__tests__/LighthouseReport_.test.res
@@ -44,6 +44,18 @@ test("artifact-name CLI rejects an invalid environment", async () => {
   expect(result.stderr)->toContain("Invalid Lighthouse deployment environment: staging")
 })
 
+test("artifact-name CLI follows the renamed production branch", async () => {
+  let state = await workspace()
+  let result = run(state, ["artifact-name", "v12", "production", "v12"], ())
+  expectSuccess(result)
+  let production = artifactName("v12", ~environment="production", ~productionBranch="v12")
+  expect(result.stdout)->toBe(`${production}\n`)
+  expect(production)->toBe(artifactName("v12", ~productionBranch="v12"))
+  expect(production != artifactName("v12", ~environment="preview", ~productionBranch="v12"))->toBe(
+    true,
+  )
+})
+
 for_([[], [""]])("artifact-name CLI rejects missing or empty branch %j", async arguments => {
   let state = await workspace()
   let result = run(state, ["artifact-name", ...arguments], ())
diff --git a/apps/docs/scripts/__tests__/LighthouseWorkflowFixtures.res b/apps/docs/scripts/__tests__/LighthouseWorkflowFixtures.res
index 50dd575e0..5502cb955 100644
--- a/apps/docs/scripts/__tests__/LighthouseWorkflowFixtures.res
+++ b/apps/docs/scripts/__tests__/LighthouseWorkflowFixtures.res
@@ -62,6 +62,7 @@ let fixture = async (~overrides=[], ()) => {
         ("CALLS", join([directory, "calls.jsonl"])),
         ("GITHUB_ENV", join([directory, "environment"])),
         ("GITHUB_EVENT_NAME", "pull_request"),
+        ("PRODUCTION_BRANCH", "master"),
         ("DEPLOY_ENVIRONMENT", ""),
         ("DOCS_DEPLOYMENT_ENVIRONMENT", ""),
         ("GITHUB_REPOSITORY", "owner/site"),
diff --git a/apps/docs/scripts/__tests__/LighthouseWorkflow_.test.res b/apps/docs/scripts/__tests__/LighthouseWorkflow_.test.res
index 7c8ec1bbf..65ae8526a 100644
--- a/apps/docs/scripts/__tests__/LighthouseWorkflow_.test.res
+++ b/apps/docs/scripts/__tests__/LighthouseWorkflow_.test.res
@@ -41,6 +41,22 @@ test("preview PR audits compare against the target branch's default environment"
   expect(environment)->toContain("LIGHTHOUSE_TARGET_BRANCH=master\n")
 })
 
+test("PR audits use the renamed default branch's production baseline", async () => {
+  let state = await Workflow.fixture(
+    ~overrides=[
+      ("PRODUCTION_BRANCH", "v12"),
+      ("GH_RESPONSE", "v12\n"),
+      ("DOCS_DEPLOYMENT_ENVIRONMENT", "preview"),
+    ],
+    (),
+  )
+  expectSuccess(Workflow.run("lighthouse-environment.sh", state))
+  let environment = await Workflow.environmentContents(state)
+  let artifact = LighthouseFixtures.artifactName("v12", ~productionBranch="v12")
+  expect(environment)->toContain(`LIGHTHOUSE_TARGET_ARTIFACT_NAME=${artifact}\n`)
+  expect(environment)->toContain("LIGHTHOUSE_TARGET_BRANCH=v12\n")
+})
+
 let productionEnvironment = "SAFE_BRANCH=master\nDOCS_DEPLOYMENT_ENVIRONMENT=production\nVITE_DEPLOYMENT_URL=\nDOCS_DEPLOYMENT_URL=https://rescript-lang.org\n"
 let homepagePreviewEnvironment = "SAFE_BRANCH=perf-homepage-19ab1c0e\nDOCS_DEPLOYMENT_ENVIRONMENT=preview\nVITE_DEPLOYMENT_URL=https://perf-homepage-19ab1c0e.rescript-lang.pages.dev\nDOCS_DEPLOYMENT_URL=https://perf-homepage-19ab1c0e.rescript-lang.pages.dev\n"
 let masterPreviewEnvironment = "SAFE_BRANCH=master-fc613b4d\nDOCS_DEPLOYMENT_ENVIRONMENT=preview\nVITE_DEPLOYMENT_URL=https://master-fc613b4d.rescript-lang.pages.dev\nDOCS_DEPLOYMENT_URL=https://master-fc613b4d.rescript-lang.pages.dev\n"
@@ -99,6 +115,37 @@ for_([
   expect(exists(join([state.directory, "calls.jsonl"])))->toBe(false)
 })
 
+let v12ProductionEnvironment = "SAFE_BRANCH=v12\nDOCS_DEPLOYMENT_ENVIRONMENT=production\nVITE_DEPLOYMENT_URL=\nDOCS_DEPLOYMENT_URL=https://rescript-lang.org\n"
+let v12PreviewEnvironment = "SAFE_BRANCH=v12-2ab8c63a\nDOCS_DEPLOYMENT_ENVIRONMENT=preview\nVITE_DEPLOYMENT_URL=https://v12-2ab8c63a.rescript-lang.pages.dev\nDOCS_DEPLOYMENT_URL=https://v12-2ab8c63a.rescript-lang.pages.dev\n"
+
+for_([
+  ("push", "v12", "", v12ProductionEnvironment),
+  ("push", "master", "", masterPreviewEnvironment),
+  ("pull_request", "v12", "", v12PreviewEnvironment),
+  ("workflow_dispatch", "v12", "preview", v12PreviewEnvironment),
+  ("workflow_dispatch", "v12", "production", v12ProductionEnvironment),
+  ("workflow_dispatch", "Perf/Homepage", "production", v12ProductionEnvironment),
+])("deployment after the rename for %s on %s with selection '%s'", async ((
+  event,
+  branch,
+  selection,
+  expectedEnvironment,
+)) => {
+  let state = await Workflow.fixture(
+    ~overrides=[
+      ("PRODUCTION_BRANCH", "v12"),
+      ("GITHUB_EVENT_NAME", event),
+      ("RAW_BRANCH", branch),
+      ("DEPLOY_ENVIRONMENT", selection),
+      ("GH_FAIL", "1"),
+    ],
+    (),
+  )
+  expectSuccess(Workflow.run("deployment-environment.sh", state))
+  expect(await Workflow.environmentContents(state))->toBe(expectedEnvironment)
+  expect(exists(join([state.directory, "calls.jsonl"])))->toBe(false)
+})
+
 for_([
   ("perf/fonts", "perf-fonts", "perf-fonts-a9ef7a11", "perf-fonts-a7ec124a"),
   (
diff --git a/apps/docs/scripts/lighthouse-report.mjs b/apps/docs/scripts/lighthouse-report.mjs
index 15d5e2150..b088b6eaf 100644
--- a/apps/docs/scripts/lighthouse-report.mjs
+++ b/apps/docs/scripts/lighthouse-report.mjs
@@ -17,15 +17,20 @@ const reportCategoryKeys = {
   seo: "seo",
 };
 
-export function lighthouseArtifactName(branch, environment) {
-  const defaultEnvironment = branch === "master" ? "production" : "preview";
+export function lighthouseArtifactName(
+  branch,
+  environment,
+  productionBranch = "master",
+) {
+  const defaultEnvironment =
+    branch === productionBranch ? "production" : "preview";
   const effectiveEnvironment = environment || defaultEnvironment;
   if (!["production", "preview"].includes(effectiveEnvironment)) {
     throw new Error(
       `Invalid Lighthouse deployment environment: ${effectiveEnvironment}`,
     );
   }
-  // Preserve existing production-master and branch-preview keys. Alternative
+  // Preserve existing production and branch-preview keys. Alternative
   // environments use a separate identity so they cannot overwrite those keys.
   const isDefaultEnvironment = effectiveEnvironment === defaultEnvironment;
   const identity = isDefaultEnvironment
@@ -240,13 +245,13 @@ async function writeComment() {
   );
 }
 
-async function main(command, branch, environment) {
+async function main(command, branch, environment, productionBranch) {
   if (command === "artifact-name") {
     if (!branch) {
       throw new Error("A branch name is required for artifact-name");
     }
 
-    console.log(lighthouseArtifactName(branch, environment));
+    console.log(lighthouseArtifactName(branch, environment, productionBranch));
     return;
   }
 
@@ -268,5 +273,10 @@ const entryPath = process.argv[1]
   : "";
 
 if (import.meta.url === entryPath) {
-  await main(process.argv[2], process.argv[3], process.argv[4]);
+  await main(
+    process.argv[2],
+    process.argv[3],
+    process.argv[4],
+    process.argv[5],
+  );
 }
diff --git a/apps/guide/README.md b/apps/guide/README.md
index 9504eec65..f257f320e 100644
--- a/apps/guide/README.md
+++ b/apps/guide/README.md
@@ -97,7 +97,7 @@ interactive compiler and runtime then run in the learner's browser.
   editor drafts, pane sizes, and theme in browser local storage.
 - Browser history support, light and dark themes, resizable instruction/output
   panes, Cloudflare preview deployments, and production deployment from
-  `master`.
+  the repository's default branch.
 
 The current interface is intentionally desktop-only: widths below `1024px`
 show a stop screen rather than a usable guide.
@@ -134,6 +134,6 @@ Track outstanding guide launch work in this checklist:
 ## Deployment
 
 The `deploy-guide` job in `.github/workflows/deploy.yml` builds the guide and
-deploys its `build/client/` assets with Wrangler. Pushes to `master` deploy the
+deploys its `build/client/` assets with Wrangler. Pushes to the default branch deploy the
 production Worker; non-Dependabot pull requests from this repository receive a preview Worker
 version and a link in the pull request.