diff --git a/backend/src/ref_backend/core/config.py b/backend/src/ref_backend/core/config.py
index 8f192314..fffede1d 100644
--- a/backend/src/ref_backend/core/config.py
+++ b/backend/src/ref_backend/core/config.py
@@ -30,7 +30,7 @@ class Settings(BaseSettings):
     API_V1_STR: str = "/api/v1"
     FRONTEND_HOST: str = "http://localhost:5173"
     BACKEND_HOST: str = "http://localhost:8000"
-    ENVIRONMENT: Literal["local", "staging", "production"] = "local"
+    ENVIRONMENT: Literal["local", "staging", "preview", "production"] = "local"
     LOG_LEVEL: str = "INFO"
     GIT_COMMIT: str | None = None
     """Commit the image was built from, set at build time."""
diff --git a/backend/src/ref_backend/models/about.py b/backend/src/ref_backend/models/about.py
index bb4e23f5..8224c2c4 100644
--- a/backend/src/ref_backend/models/about.py
+++ b/backend/src/ref_backend/models/about.py
@@ -19,7 +19,7 @@ class About(BaseModel):
     last_updated: datetime | None
     """When an execution group was last updated, or None if there are no executions."""
 
-    environment: Literal["local", "staging", "production"]
+    environment: Literal["local", "staging", "preview", "production"]
     """
     The deployment this API is serving.
 
diff --git a/backend/tests/test_core/test_config.py b/backend/tests/test_core/test_config.py
index 08ae5f97..de58daee 100644
--- a/backend/tests/test_core/test_config.py
+++ b/backend/tests/test_core/test_config.py
@@ -1,6 +1,6 @@
 """Tests for the Settings CORS parsing."""
 
-from ref_backend.core.config import parse_cors
+from ref_backend.core.config import Settings, parse_cors
 
 
 class TestParseCors:
@@ -15,3 +15,9 @@ def test_list_passes_through(self):
         """A list value passes through unchanged."""
         result = parse_cors(["http://a.example", "http://b.example"])
         assert result == ["http://a.example", "http://b.example"]
+
+
+def test_preview_environment_is_accepted(monkeypatch):
+    """Pull request previews deploy with ENVIRONMENT=preview."""
+    monkeypatch.setenv("ENVIRONMENT", "preview")
+    assert Settings().ENVIRONMENT == "preview"
diff --git a/changelog/141.fix.md b/changelog/141.fix.md
new file mode 100644
index 00000000..81058dec
--- /dev/null
+++ b/changelog/141.fix.md
@@ -0,0 +1 @@
+Pull request previews now start, and show the staging banner and sparse results like the staging site.
diff --git a/frontend/src/client/types.gen.ts b/frontend/src/client/types.gen.ts
index 2aeb20ed..7ad35540 100644
--- a/frontend/src/client/types.gen.ts
+++ b/frontend/src/client/types.gen.ts
@@ -400,7 +400,7 @@ export type About = {
     /**
      * Environment
      */
-    environment: 'local' | 'staging' | 'production';
+    environment: 'local' | 'staging' | 'preview' | 'production';
 };
 
 /**
diff --git a/frontend/src/components/app/stagingBanner.test.tsx b/frontend/src/components/app/stagingBanner.test.tsx
index 5b61ddcc..a91ad6b8 100644
--- a/frontend/src/components/app/stagingBanner.test.tsx
+++ b/frontend/src/components/app/stagingBanner.test.tsx
@@ -4,7 +4,7 @@ import { describe, expect, it } from "vitest";
 import { utilsAboutOptions } from "@/client/@tanstack/react-query.gen";
 import { StagingBanner } from "./stagingBanner";
 
-const renderBanner = (environment?: "production" | "staging") => {
+const renderBanner = (environment?: "production" | "staging" | "preview") => {
   const queryClient = new QueryClient({
     defaultOptions: { queries: { retry: false } },
   });
@@ -30,6 +30,11 @@ describe("StagingBanner", () => {
     expect(screen.getByText(/Staging site/)).toBeInTheDocument();
   });
 
+  it("names a pull request preview as staging", () => {
+    renderBanner("preview");
+    expect(screen.getByText(/Staging site/)).toBeInTheDocument();
+  });
+
   it("stays out of the way in production", () => {
     renderBanner("production");
     expect(screen.queryByText(/Staging site/)).not.toBeInTheDocument();
diff --git a/frontend/src/components/charts/mipEraSections.test.tsx b/frontend/src/components/charts/mipEraSections.test.tsx
index 9a43b139..5b097348 100644
--- a/frontend/src/components/charts/mipEraSections.test.tsx
+++ b/frontend/src/components/charts/mipEraSections.test.tsx
@@ -20,7 +20,7 @@ const four = (era: string | undefined) =>
 const renderChart = (
   values: ReturnType<typeof model>[],
   mipEra?: "CMIP6" | "CMIP7",
-  environment: "production" | "staging" = "production",
+  environment: "production" | "staging" | "preview" = "production",
 ) => {
   const queryClient = new QueryClient({
     defaultOptions: { queries: { retry: false } },
@@ -113,4 +113,12 @@ describe("MipEraSections with a page selection", () => {
       screen.queryByText("Not enough models to plot"),
     ).not.toBeInTheDocument();
   });
+
+  it("plots a chart with too few models on a preview site", () => {
+    renderChart([model("CMIP6", "A"), model("CMIP6", "B")], "CMIP6", "preview");
+    expect(screen.getByTestId("chart")).toBeInTheDocument();
+    expect(
+      screen.queryByText("Not enough models to plot"),
+    ).not.toBeInTheDocument();
+  });
 });
diff --git a/frontend/src/hooks/useStagingMode.ts b/frontend/src/hooks/useStagingMode.ts
index 3e09a027..534c3335 100644
--- a/frontend/src/hooks/useStagingMode.ts
+++ b/frontend/src/hooks/useStagingMode.ts
@@ -2,6 +2,10 @@ import { useQuery } from "@tanstack/react-query";
 import { utilsAboutOptions } from "@/client/@tanstack/react-query.gen";
 import { getDefaultApiEndpoint } from "@/lib/apiEndpoint";
 
+// A pull request preview serves unreleased code, so it is a staging site too.
+const isStagingEnvironment = (environment?: string) =>
+  environment === "staging" || environment === "preview";
+
 /**
  * Whether the API being read is a staging deployment.
  *
@@ -10,7 +14,7 @@ import { getDefaultApiEndpoint } from "@/lib/apiEndpoint";
  */
 export function useStagingMode(): boolean {
   const { data } = useQuery(utilsAboutOptions());
-  return data?.environment === "staging";
+  return isStagingEnvironment(data?.environment);
 }
 
 /**
@@ -23,5 +27,5 @@ export function useStagingDashboard(): boolean {
   const { data } = useQuery(
     utilsAboutOptions({ baseUrl: getDefaultApiEndpoint() }),
   );
-  return data?.environment === "staging";
+  return isStagingEnvironment(data?.environment);
 }