diff --git a/apps/mobile/src/features/pull-requests/PullRequestFiles.tsx b/apps/mobile/src/features/pull-requests/PullRequestFiles.tsx
index f699e46d6fb0..dc9c765bf506 100644
--- a/apps/mobile/src/features/pull-requests/PullRequestFiles.tsx
+++ b/apps/mobile/src/features/pull-requests/PullRequestFiles.tsx
@@ -1,3 +1,4 @@
+import type { PullRequestChangeBreakdown } from "@t3tools/contracts";
 import { PullRequestSectionHeading } from "./PullRequestSectionHeading";
 import { AnimatedLegendList } from "@legendapp/list/reanimated";
 import Animated from "react-native-reanimated";
@@ -23,6 +24,33 @@ import {
 import { usePullRequestFilesViewed } from "./usePullRequestFilesViewed";
 import { usePullRequestFileFilter } from "./usePullRequestFileFilter";
 
+const BREAKDOWN_LABELS = {
+  code: "Code",
+  tests: "Tests",
+  mocks: "Mocks",
+  generated: "Generated",
+} satisfies Record<keyof NonNullable<PullRequestChangeBreakdown>, string>;
+
+function PullRequestChangeBreakdownLine(props: {
+  readonly breakdown: NonNullable<PullRequestChangeBreakdown>;
+}) {
+  const parts = (Object.keys(BREAKDOWN_LABELS) as Array<keyof typeof BREAKDOWN_LABELS>).flatMap(
+    (kind) => {
+      const { additions, deletions } = props.breakdown[kind];
+      return additions === 0 && deletions === 0
+        ? []
+        : [
+            `${BREAKDOWN_LABELS[kind]} +${additions.toLocaleString()} −${deletions.toLocaleString()}`,
+          ];
+    },
+  );
+  return (
+    <Text className="text-2xs tabular-nums text-foreground-muted" numberOfLines={2}>
+      {parts.join(" · ")}
+    </Text>
+  );
+}
+
 function fileDirectory(path: string) {
   const separator = path.lastIndexOf("/");
   return separator < 0 ? "" : path.slice(0, separator);
@@ -37,6 +65,9 @@ export function usePullRequestFilesContent(props: {
   const result = usePullRequestDiff(props.params);
   const detail = useEnvironmentQuery(composerPullRequests.detail(requestTarget(props.params)));
   const viewed = usePullRequestFilesViewed(props.params, props.params.commit ? null : detail.data);
+  const breakdown = useEnvironmentQuery(
+    props.params.commit ? null : composerPullRequests.changeBreakdown(requestTarget(props.params)),
+  ).data;
   const filter = usePullRequestFileFilter(result.parsed);
   const parsed = filter.parsed;
   const loading = result.isPending && parsed.kind === "empty" && !result.error;
@@ -209,6 +240,7 @@ export function usePullRequestFilesContent(props: {
                     ? `${filter.hiddenCount} test ${filter.hiddenCount === 1 ? "file" : "files"} hidden`
                     : "Test files included"}
                 </Text>
+                {breakdown ? <PullRequestChangeBreakdownLine breakdown={breakdown} /> : null}
               </View>
               <PullRequestDiffStats
                 additions={parsed.additions}
diff --git a/apps/mobile/src/features/pull-requests/pullRequestFileFilters.ts b/apps/mobile/src/features/pull-requests/pullRequestFileFilters.ts
index a8c9f0209e43..2d8e3a94fe4b 100644
--- a/apps/mobile/src/features/pull-requests/pullRequestFileFilters.ts
+++ b/apps/mobile/src/features/pull-requests/pullRequestFileFilters.ts
@@ -1,19 +1,10 @@
+import { classifyChangedFile } from "@t3tools/shared/changedFileKind";
 import type { ReviewParsedDiff } from "../review/reviewModel";
 
+/** Test support such as fixtures and snapshots is hidden along with the tests. */
 export function isPullRequestTestFile(path: string): boolean {
-  const segments = path.replaceAll("\\", "/").split("/");
-  const name = segments.at(-1) ?? "";
-  return (
-    segments
-      .slice(0, -1)
-      .some((segment) => /^(?:__tests__|__snapshots__|tests?|spec|e2e)$/i.test(segment)) ||
-    /\.(?:test|spec)\./i.test(name) ||
-    /\.snap$/i.test(name) ||
-    /^(?:test_.+|.+_test)\.py$/i.test(name) ||
-    /_test\.(?:go|rs|rb|c|cc|cpp|h|hpp)$/i.test(name) ||
-    /(?:Test|Tests|Spec)\.(?:java|kt|kts|swift|cs)$/.test(name) ||
-    /_spec\.rb$/i.test(name)
-  );
+  const kind = classifyChangedFile(path);
+  return kind === "tests" || kind === "mocks";
 }
 
 export function filterPullRequestTestFiles(
diff --git a/apps/server/src/auth/RpcAuthorization.ts b/apps/server/src/auth/RpcAuthorization.ts
index 30e0ca31a594..3ada3a069823 100644
--- a/apps/server/src/auth/RpcAuthorization.ts
+++ b/apps/server/src/auth/RpcAuthorization.ts
@@ -133,6 +133,7 @@ export const RPC_REQUIRED_SCOPES = {
   [WS_METHODS.pullRequestsThreadComments]: AuthOrchestrationReadScope,
   [WS_METHODS.pullRequestsDiffFileContents]: AuthOrchestrationReadScope,
   [WS_METHODS.pullRequestsFilesViewed]: AuthOrchestrationReadScope,
+  [WS_METHODS.pullRequestsChangeBreakdown]: AuthOrchestrationReadScope,
   [WS_METHODS.pullRequestsInvalidate]: AuthOrchestrationReadScope,
   [WS_METHODS.pullRequestsReportState]: AuthOrchestrationReadScope,
   [WS_METHODS.pullRequestsSubscribeRefreshes]: AuthOrchestrationReadScope,
diff --git a/apps/server/src/observability/RpcInstrumentation.ts b/apps/server/src/observability/RpcInstrumentation.ts
index 161694d55cb8..33a73bf3b47c 100644
--- a/apps/server/src/observability/RpcInstrumentation.ts
+++ b/apps/server/src/observability/RpcInstrumentation.ts
@@ -113,6 +113,7 @@ const RPC_AGGREGATES = {
   [WS_METHODS.pullRequestsThreadComments]: "pull-requests",
   [WS_METHODS.pullRequestsDiffFileContents]: "pull-requests",
   [WS_METHODS.pullRequestsFilesViewed]: "pull-requests",
+  [WS_METHODS.pullRequestsChangeBreakdown]: "pull-requests",
   [WS_METHODS.pullRequestsRunAction]: "pull-requests",
   [WS_METHODS.pullRequestsUpdate]: "pull-requests",
   [WS_METHODS.pullRequestsComment]: "pull-requests",
diff --git a/apps/server/src/pullRequest/PullRequestService.ts b/apps/server/src/pullRequest/PullRequestService.ts
index 4bac77b4ac0b..f0c2b580064a 100644
--- a/apps/server/src/pullRequest/PullRequestService.ts
+++ b/apps/server/src/pullRequest/PullRequestService.ts
@@ -40,6 +40,7 @@ import {
   type PullRequestDiffFileContentsResult,
   type PullRequestDiffStat,
   type PullRequestDiffInput,
+  type PullRequestChangeBreakdown,
   type PullRequestFilesViewedResult,
   type PullRequestDiffResult,
   type PullRequestInvalidateInput,
@@ -95,6 +96,7 @@ import {
 import * as PullRequestReadCache from "./PullRequestReadCache.ts";
 import * as PullRequestProviderRegistry from "./PullRequestProviderRegistry.ts";
 import * as ViewedFiles from "./pullRequestViewedFiles.ts";
+import { toChangeBreakdown } from "./pullRequestChangeBreakdown.ts";
 
 export interface PullRequestMergeEvent extends PullRequestRef {
   readonly mergedAt: string;
@@ -230,6 +232,9 @@ export class PullRequestService extends Context.Service<
     readonly setFilesViewed: (
       input: PullRequestSetFilesViewedInput,
     ) => Effect.Effect<void, PullRequestError>;
+    readonly changeBreakdown: (
+      input: PullRequestRef,
+    ) => Effect.Effect<PullRequestChangeBreakdown, PullRequestError>;
     readonly runAction: (input: PullRequestActionInput) => Effect.Effect<void, PullRequestError>;
     readonly update: (input: PullRequestUpdateInput) => Effect.Effect<void, PullRequestError>;
     readonly comment: (input: PullRequestCommentInput) => Effect.Effect<void, PullRequestError>;
@@ -535,6 +540,9 @@ function withRateLimitBackoff(
     ...(api.getFilesViewed === undefined
       ? {}
       : { getFilesViewed: wrap("getFilesViewed", api.getFilesViewed) }),
+    ...(api.getFileStats === undefined
+      ? {}
+      : { getFileStats: wrap("getFileStats", api.getFileStats) }),
     ...(api.setFilesViewed === undefined
       ? {}
       : { setFilesViewed: interactive("setFilesViewed", api.setFilesViewed) }),
@@ -2958,6 +2966,32 @@ export const make = Effect.gen(function* () {
     },
   );
 
+  const changeBreakdownCache = yield* Cache.makeWith(
+    (key: string) => {
+      const ref = refOfCacheKey(key);
+      return requireProject(ref).pipe(
+        Effect.flatMap((project) => {
+          const read = project.api.getFileStats;
+          if (read === undefined) return Effect.succeed(null);
+          return read({
+            cwd: project.project.workspaceRoot,
+            repository: project.repository,
+            host: project.host,
+            number: ref.number,
+          }).pipe(
+            Effect.map(toChangeBreakdown),
+            Effect.mapError(toPullRequestError("changeBreakdown")),
+          );
+        }),
+      );
+    },
+    {
+      capacity: DETAIL_CACHE_CAPACITY,
+      timeToLive: (exit, key) =>
+        Exit.isSuccess(exit) ? detailTimeToLive(lastGoodSummary.peek(key)?.state) : Duration.zero,
+    },
+  );
+
   const previewCache = yield* Cache.makeWith(
     (key: string) => {
       return previewUncached(refOfCacheKey(key));
@@ -3366,6 +3400,9 @@ export const make = Effect.gen(function* () {
     diffFileContents,
     filesViewed: credentialCached(filesViewed),
     setFilesViewed,
+    changeBreakdown: credentialCached((input) =>
+      Cache.get(changeBreakdownCache, refCacheKey(input)),
+    ),
     runAction: runActionAndInvalidate,
     update: invalidatedByMutation(update),
     comment: invalidatedByMutation(comment),
diff --git a/apps/server/src/pullRequest/pullRequestChangeBreakdown.test.ts b/apps/server/src/pullRequest/pullRequestChangeBreakdown.test.ts
new file mode 100644
index 000000000000..68321f39eb22
--- /dev/null
+++ b/apps/server/src/pullRequest/pullRequestChangeBreakdown.test.ts
@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vite-plus/test";
+
+import { toChangeBreakdown } from "./pullRequestChangeBreakdown.ts";
+
+describe("toChangeBreakdown", () => {
+  it("sums line counts per kind", () => {
+    expect(
+      toChangeBreakdown({
+        truncated: false,
+        files: [
+          { path: "src/a.ts", additions: 10, deletions: 2 },
+          { path: "src/b.ts", additions: 5, deletions: 1 },
+          { path: "src/a.test.ts", additions: 40, deletions: 0 },
+          { path: "pnpm-lock.yaml", additions: 300, deletions: 120 },
+        ],
+      }),
+    ).toEqual({
+      code: { additions: 15, deletions: 3 },
+      tests: { additions: 40, deletions: 0 },
+      mocks: { additions: 0, deletions: 0 },
+      generated: { additions: 300, deletions: 120 },
+    });
+  });
+
+  it("gives no breakdown for a partial file list", () => {
+    expect(
+      toChangeBreakdown({
+        truncated: true,
+        files: [{ path: "src/a.ts", additions: 1, deletions: 0 }],
+      }),
+    ).toBeNull();
+  });
+});
diff --git a/apps/server/src/pullRequest/pullRequestChangeBreakdown.ts b/apps/server/src/pullRequest/pullRequestChangeBreakdown.ts
new file mode 100644
index 000000000000..77d8162e8956
--- /dev/null
+++ b/apps/server/src/pullRequest/pullRequestChangeBreakdown.ts
@@ -0,0 +1,15 @@
+import type { PullRequestChangeBreakdown } from "@t3tools/contracts";
+import { classifyChangedFile } from "@t3tools/shared/changedFileKind";
+import type { ProviderFileStats } from "@t3tools/source-control-core/server/PullRequestProvider";
+
+export function toChangeBreakdown(stats: ProviderFileStats): PullRequestChangeBreakdown {
+  if (stats.truncated) return null;
+  const empty = () => ({ additions: 0, deletions: 0 });
+  const breakdown = { code: empty(), tests: empty(), mocks: empty(), generated: empty() };
+  for (const file of stats.files) {
+    const bucket = breakdown[classifyChangedFile(file.path)];
+    bucket.additions += file.additions;
+    bucket.deletions += file.deletions;
+  }
+  return breakdown;
+}
diff --git a/apps/server/src/ws.ts b/apps/server/src/ws.ts
index 88b0be990467..1ebd8950dea0 100644
--- a/apps/server/src/ws.ts
+++ b/apps/server/src/ws.ts
@@ -2487,6 +2487,8 @@ export const layerWsRpc = (
           withPullRequestViewer(input, pullRequests.diffFileContents(input)),
         [WS_METHODS.pullRequestsFilesViewed]: (input) =>
           withPullRequestViewer(input, pullRequests.filesViewed(input)),
+        [WS_METHODS.pullRequestsChangeBreakdown]: (input) =>
+          withPullRequestViewer(input, pullRequests.changeBreakdown(input)),
         [WS_METHODS.pullRequestsSetFilesViewed]: (input) =>
           withPullRequestViewer(input, pullRequests.setFilesViewed(input)),
         [WS_METHODS.pullRequestsRunAction]: (input) =>
diff --git a/apps/web/src/components/pullRequest/PullRequestChangeBreakdownStat.tsx b/apps/web/src/components/pullRequest/PullRequestChangeBreakdownStat.tsx
new file mode 100644
index 000000000000..cba047e2a416
--- /dev/null
+++ b/apps/web/src/components/pullRequest/PullRequestChangeBreakdownStat.tsx
@@ -0,0 +1,100 @@
+import { formatDiffCount } from "@t3tools/client-runtime/diff-count";
+import type { EnvironmentId, PullRequestChangeBreakdown, PullRequestRef } from "@t3tools/contracts";
+import { useState } from "react";
+
+import { pullRequestEnvironment } from "~/state/pullRequests";
+import { useEnvironmentQuery } from "~/state/query";
+
+import { Tooltip, TooltipPopup, TooltipTrigger } from "../ui/tooltip";
+import { PullRequestDiffStat } from "./pullRequestPresentation";
+
+const KIND_LABELS = {
+  code: "Code",
+  tests: "Tests",
+  mocks: "Mocks",
+  generated: "Generated",
+} satisfies Record<keyof NonNullable<PullRequestChangeBreakdown>, string>;
+
+/**
+ * The pull request's diff stat, with a hover split into code, tests, mocks, and generated files.
+ * The split is read on first pointer or focus intent, so a page nobody hovers costs the host
+ * nothing.
+ */
+export function PullRequestChangeBreakdownStat({
+  environmentId,
+  reference,
+  additions,
+  deletions,
+  className,
+}: {
+  environmentId: EnvironmentId;
+  reference: PullRequestRef;
+  additions: number;
+  deletions: number;
+  className: string;
+}) {
+  const [requested, setRequested] = useState(false);
+  const query = useEnvironmentQuery(
+    requested ? pullRequestEnvironment.changeBreakdown({ environmentId, input: reference }) : null,
+  );
+  const breakdown = query.data;
+  if (additions === 0 && deletions === 0) return null;
+  return (
+    <Tooltip>
+      <TooltipTrigger
+        onPointerEnter={() => setRequested(true)}
+        onFocus={() => setRequested(true)}
+        render={
+          <span className="inline-flex">
+            <PullRequestDiffStat
+              additions={additions}
+              deletions={deletions}
+              className={className}
+            />
+          </span>
+        }
+      />
+      {breakdown ? (
+        <TooltipPopup side="bottom">
+          <div className="grid grid-cols-[auto_auto_auto] gap-x-4 gap-y-1 py-0.5 font-mono tabular-nums">
+            {(Object.keys(KIND_LABELS) as Array<keyof typeof KIND_LABELS>).map((kind) => {
+              const { additions, deletions } = breakdown[kind];
+              return additions === 0 && deletions === 0 ? null : (
+                <BreakdownRow
+                  key={kind}
+                  label={KIND_LABELS[kind]}
+                  additions={additions}
+                  deletions={deletions}
+                />
+              );
+            })}
+            <div className="col-span-3 border-t border-border" />
+            <BreakdownRow label="Total" additions={additions} deletions={deletions} />
+          </div>
+        </TooltipPopup>
+      ) : query.isPending ? (
+        <TooltipPopup side="bottom">Loading breakdown</TooltipPopup>
+      ) : null}
+    </Tooltip>
+  );
+}
+
+function BreakdownRow({
+  label,
+  additions,
+  deletions,
+}: {
+  label: string;
+  additions: number;
+  deletions: number;
+}) {
+  return (
+    <>
+      <span className="font-sans">{label}</span>
+      <span className="text-right text-diff-addition-foreground">
+        +{formatDiffCount(additions)}
+      </span>
+      <span className="text-right text-diff-deletion">-{formatDiffCount(deletions)}</span>
+    </>
+  );
+}
diff --git a/apps/web/src/components/pullRequest/PullRequestDetailPanel.tsx b/apps/web/src/components/pullRequest/PullRequestDetailPanel.tsx
index 071b77b39db5..33c87722ff50 100644
--- a/apps/web/src/components/pullRequest/PullRequestDetailPanel.tsx
+++ b/apps/web/src/components/pullRequest/PullRequestDetailPanel.tsx
@@ -97,6 +97,7 @@ import {
 } from "~/state/pullRequests";
 import { useAtomCommand } from "~/state/use-atom-command";
 import { PullRequestStackMenu } from "./PullRequestStackMenu";
+import { PullRequestChangeBreakdownStat } from "./PullRequestChangeBreakdownStat";
 import { sourceControlClients } from "@t3tools/client-runtime/source-control-clients";
 import { PullRequestThreadLinks } from "./PullRequestThreadLinks";
 import { vcsEnvironment } from "~/state/vcs";
@@ -182,7 +183,6 @@ import {
 import { PullRequestChecksPopover } from "./PullRequestChecksPopover";
 import {
   PullRequestActorLabel,
-  PullRequestDiffStat,
   PullRequestMetaLine,
   PullRequestReviewOutcomeIcon,
   pullRequestChecksState,
@@ -2430,7 +2430,9 @@ export function PullRequestDetailPanel({
                       <FileDiffIcon aria-hidden className="size-3" />
                       {detail.changedFiles.toLocaleString()}
                     </span>
-                    <PullRequestDiffStat
+                    <PullRequestChangeBreakdownStat
+                      environmentId={environmentId}
+                      reference={reference}
                       additions={detail.additions}
                       deletions={detail.deletions}
                       className="shrink-0 font-mono text-2xs"
@@ -2604,7 +2606,9 @@ export function PullRequestDetailPanel({
                 }
                 files={`${detail.changedFiles.toLocaleString()} ${detail.changedFiles === 1 ? "file" : "files"}`}
                 diffStat={
-                  <PullRequestDiffStat
+                  <PullRequestChangeBreakdownStat
+                    environmentId={environmentId}
+                    reference={reference}
                     additions={detail.additions}
                     deletions={detail.deletions}
                     className="shrink-0 font-mono text-xs"
diff --git a/packages/client-runtime/src/state/pullRequestRouting.ts b/packages/client-runtime/src/state/pullRequestRouting.ts
index 8bdcb481c5f0..73624f97b48b 100644
--- a/packages/client-runtime/src/state/pullRequestRouting.ts
+++ b/packages/client-runtime/src/state/pullRequestRouting.ts
@@ -41,6 +41,7 @@ const reads = new Set<string>([
   WS_METHODS.pullRequestsThreadComments,
   WS_METHODS.pullRequestsDiffFileContents,
   WS_METHODS.pullRequestsFilesViewed,
+  WS_METHODS.pullRequestsChangeBreakdown,
   WS_METHODS.pullRequestsReviewerCandidates,
   WS_METHODS.pullRequestsLabelCandidates,
 ]);
diff --git a/packages/client-runtime/src/state/pullRequests.ts b/packages/client-runtime/src/state/pullRequests.ts
index 684c3d1999f8..757037734479 100644
--- a/packages/client-runtime/src/state/pullRequests.ts
+++ b/packages/client-runtime/src/state/pullRequests.ts
@@ -7,6 +7,7 @@ import {
   PullRequestListResult,
   PullRequestChecks,
   PullRequestDiffResult,
+  PullRequestChangeBreakdown,
   PullRequestFilesViewedResult,
   PullRequestLinkedThreadsResult,
   type EnvironmentId,
@@ -372,6 +373,14 @@ export function createPullRequestEnvironmentAtoms<R, E>(
       execute: (input) => routedRequest(WS_METHODS.pullRequestsFilesViewed, input),
       staleTimeMs: 15_000,
     }),
+    changeBreakdown: createEnvironmentRpcQueryAtomFamily(runtime, {
+      label: "environment-data:pull-requests:change-breakdown",
+      persistence: persistQuery(PullRequestChangeBreakdown),
+      tag: WS_METHODS.pullRequestsChangeBreakdown,
+      execute: (input) => routedRequest(WS_METHODS.pullRequestsChangeBreakdown, input),
+      staleTimeMs: 60_000,
+      refreshTrigger: ({ environmentId }) => refreshes({ environmentId, input: {} }),
+    }),
     /**
      * One write in flight per change request: the host applies these in order, and a reader
      * ticking down a file list faster than the round trip would otherwise race their own presses.
diff --git a/packages/contracts/src/pullRequest.ts b/packages/contracts/src/pullRequest.ts
index 1777dc6762f6..1bdedef24751 100644
--- a/packages/contracts/src/pullRequest.ts
+++ b/packages/contracts/src/pullRequest.ts
@@ -682,6 +682,26 @@ export const PullRequestFilesViewedResult = Schema.Struct({
 });
 export type PullRequestFilesViewedResult = typeof PullRequestFilesViewedResult.Type;
 
+const PullRequestLineCount = Schema.Struct({
+  additions: NonNegativeInt,
+  deletions: NonNegativeInt,
+});
+
+/**
+ * A change's line counts split by what the changed files are, judged from their paths. Null when
+ * the host gives no per-file counts, or has more files than one read covers: a split of part of
+ * the change would not add up to the totals shown beside it.
+ */
+export const PullRequestChangeBreakdown = Schema.NullOr(
+  Schema.Struct({
+    code: PullRequestLineCount,
+    tests: PullRequestLineCount,
+    mocks: PullRequestLineCount,
+    generated: PullRequestLineCount,
+  }),
+);
+export type PullRequestChangeBreakdown = typeof PullRequestChangeBreakdown.Type;
+
 const MAX_FILES_VIEWED_PRESSES = 500;
 
 export const PullRequestSetFilesViewedInput = Schema.Struct({
diff --git a/packages/contracts/src/rpc.ts b/packages/contracts/src/rpc.ts
index b74175d23c6f..09176ad047d6 100644
--- a/packages/contracts/src/rpc.ts
+++ b/packages/contracts/src/rpc.ts
@@ -165,6 +165,7 @@ import { PullRequestReviewGuideResult } from "./pullRequestReviewGuide.ts";
 import {
   PullRequestActionInput,
   PullRequestActivity,
+  PullRequestChangeBreakdown,
   PullRequestCommentInput,
   PullRequestCommentUpdateInput,
   PullRequestDetail,
@@ -532,6 +533,7 @@ export const WS_METHODS = {
   pullRequestsThreadComments: "pullRequests.threadComments",
   pullRequestsDiffFileContents: "pullRequests.diffFileContents",
   pullRequestsFilesViewed: "pullRequests.filesViewed",
+  pullRequestsChangeBreakdown: "pullRequests.changeBreakdown",
   pullRequestsSetFilesViewed: "pullRequests.setFilesViewed",
   pullRequestsRunAction: "pullRequests.runAction",
   pullRequestsUpdate: "pullRequests.update",
@@ -1038,6 +1040,12 @@ const WsPullRequestsFilesViewedRpc = Rpc.make(WS_METHODS.pullRequestsFilesViewed
   error: PullRequestRpcError,
 });
 
+const WsPullRequestsChangeBreakdownRpc = Rpc.make(WS_METHODS.pullRequestsChangeBreakdown, {
+  payload: PullRequestRef,
+  success: PullRequestChangeBreakdown,
+  error: PullRequestRpcError,
+});
+
 const WsPullRequestsSetFilesViewedRpc = Rpc.make(WS_METHODS.pullRequestsSetFilesViewed, {
   payload: PullRequestSetFilesViewedInput,
   success: Schema.Void,
@@ -1935,6 +1943,7 @@ export const WsRpcGroup = RpcGroup.make(
   WsPullRequestsThreadCommentsRpc,
   WsPullRequestsDiffFileContentsRpc,
   WsPullRequestsFilesViewedRpc,
+  WsPullRequestsChangeBreakdownRpc,
   WsPullRequestsSetFilesViewedRpc,
   WsPullRequestsRunActionRpc,
   WsPullRequestsUpdateRpc,
diff --git a/packages/shared/package.json b/packages/shared/package.json
index cd9137885a5c..31828017d81a 100644
--- a/packages/shared/package.json
+++ b/packages/shared/package.json
@@ -3,6 +3,10 @@
   "private": true,
   "type": "module",
   "exports": {
+    "./changedFileKind": {
+      "types": "./src/changedFileKind.ts",
+      "import": "./src/changedFileKind.ts"
+    },
     "./githubMarkdownLinks": {
       "types": "./src/githubMarkdownLinks.ts",
       "import": "./src/githubMarkdownLinks.ts"
diff --git a/packages/shared/src/changedFileKind.test.ts b/packages/shared/src/changedFileKind.test.ts
new file mode 100644
index 000000000000..a3a8fd62faea
--- /dev/null
+++ b/packages/shared/src/changedFileKind.test.ts
@@ -0,0 +1,42 @@
+import { describe, expect, it } from "vite-plus/test";
+
+import { classifyChangedFile } from "./changedFileKind.ts";
+
+describe("classifyChangedFile", () => {
+  it.each([
+    ["apps/server/src/ws.ts", "code"],
+    ["src/latest.ts", "code"],
+    ["src/Latest.java", "code"],
+    ["src/contest.py", "code"],
+    ["src/mockingbird.ts", "code"],
+    ["src/testimonials/List.tsx", "code"],
+    ["apps/web/src/foo.test.ts", "tests"],
+    ["apps/web/src/Foo.browser.test.tsx", "tests"],
+    ["src/foo.spec.js", "tests"],
+    ["pkg/server_test.go", "tests"],
+    ["tests/test_api.py", "tests"],
+    ["conftest.py", "tests"],
+    ["src/main/java/RequestTest.java", "tests"],
+    ["Sources/AppTests.swift", "tests"],
+    ["src/HTTPTest.java", "tests"],
+    ["Sources/URLTests.swift", "tests"],
+    ["spec/models/user_spec.rb", "tests"],
+    ["src/__tests__/helpers.ts", "tests"],
+    ["src/testUtils.ts", "code"],
+    ["src\\__tests__\\app.ts", "tests"],
+    ["src/__mocks__/fs.ts", "mocks"],
+    ["test/fixtures/pr.json", "mocks"],
+    ["src/__snapshots__/view.test.ts.snap", "mocks"],
+    ["src/api.mock.ts", "mocks"],
+    ["src/mockServer.ts", "mocks"],
+    ["pkg/testdata/input.txt", "mocks"],
+    ["pnpm-lock.yaml", "generated"],
+    ["apps/web/package-lock.json", "generated"],
+    ["go.sum", "generated"],
+    ["src/routeTree.gen.ts", "generated"],
+    ["src/__generated__/types.ts", "generated"],
+    ["dist/app.min.js", "generated"],
+  ] as const)("%s is %s", (path, kind) => {
+    expect(classifyChangedFile(path)).toBe(kind);
+  });
+});
diff --git a/packages/shared/src/changedFileKind.ts b/packages/shared/src/changedFileKind.ts
new file mode 100644
index 000000000000..e2d6dcbe1d75
--- /dev/null
+++ b/packages/shared/src/changedFileKind.ts
@@ -0,0 +1,76 @@
+import type { PullRequestChangeBreakdown } from "@t3tools/contracts";
+
+export type ChangedFileKind = keyof NonNullable<PullRequestChangeBreakdown>;
+
+const GENERATED_FILES = new Set([
+  "bun.lock",
+  "bun.lockb",
+  "cargo.lock",
+  "composer.lock",
+  "deno.lock",
+  "flake.lock",
+  "gemfile.lock",
+  "go.sum",
+  "gradle.lockfile",
+  "mix.lock",
+  "npm-shrinkwrap.json",
+  "package-lock.json",
+  "packages.lock.json",
+  "pipfile.lock",
+  "pnpm-lock.yaml",
+  "podfile.lock",
+  "poetry.lock",
+  "pubspec.lock",
+  "uv.lock",
+  "yarn.lock",
+]);
+const GENERATED_NAME =
+  /(\.generated\.|\.gen\.|\.g\.dart$|\.pb\.go$|_pb2(_grpc)?\.py$|\.pb\.(cc|h)$|\.min\.(js|css)$|\.(js|css)\.map$)/;
+const GENERATED_DIRS = new Set(["__generated__", "generated"]);
+
+const MOCK_NAME =
+  /(\.snap$|\.(mocks?|fixtures?|stubs?|fakes?)\.[^.]+$|^(mocks?|fixtures?|stubs?|fakes?)([-_.A-Z]|$))/;
+const MOCK_DIRS = new Set([
+  "__fixtures__",
+  "__mocks__",
+  "__snapshots__",
+  "fakes",
+  "fixture",
+  "fixtures",
+  "mock",
+  "mocks",
+  "stubs",
+  "testdata",
+]);
+
+const TEST_NAME =
+  /(\.(test|spec|e2e)\.[^.]+$|_(test|spec)\.[^.]+$|^test_.+\.py$|^conftest\.py$|^(vitest|jest)\.setup\.[^.]+$)/i;
+// Case-sensitive: `FooTest.java` is a test class, `Latest.java` is not.
+const CLASS_TEST_NAME = /(Tests?|Spec)\.(java|kt|kts|scala|groovy|cs|php|swift|m)$/;
+const TEST_DIRS = new Set([
+  "__tests__",
+  "__test__",
+  "cypress",
+  "e2e",
+  "spec",
+  "specs",
+  "test",
+  "tests",
+]);
+
+/**
+ * Sorts a changed file by its path alone, using common naming conventions. Lockfiles and build
+ * output count as generated, and test support (mocks, fixtures, snapshots) is kept apart from the
+ * tests themselves, so a reviewer can see how much of a change is logic.
+ */
+export function classifyChangedFile(path: string): ChangedFileKind {
+  const segments = path.replaceAll("\\", "/").split("/");
+  const name = segments.pop() ?? "";
+  const dirs = segments.map((segment) => segment.toLowerCase());
+  const inDir = (set: ReadonlySet<string>) => dirs.some((dir) => set.has(dir));
+  if (GENERATED_FILES.has(name.toLowerCase()) || GENERATED_NAME.test(name) || inDir(GENERATED_DIRS))
+    return "generated";
+  if (MOCK_NAME.test(name) || inDir(MOCK_DIRS)) return "mocks";
+  if (TEST_NAME.test(name) || CLASS_TEST_NAME.test(name) || inDir(TEST_DIRS)) return "tests";
+  return "code";
+}
diff --git a/packages/source-control-core/src/server/PullRequestProvider.ts b/packages/source-control-core/src/server/PullRequestProvider.ts
index 0aadb0bbc929..3bb7a757f773 100644
--- a/packages/source-control-core/src/server/PullRequestProvider.ts
+++ b/packages/source-control-core/src/server/PullRequestProvider.ts
@@ -226,6 +226,16 @@ export interface ProviderFilesViewed {
   readonly truncated: boolean;
 }
 
+export interface ProviderFileStats {
+  readonly files: ReadonlyArray<{
+    readonly path: string;
+    readonly additions: number;
+    readonly deletions: number;
+  }>;
+  /** The host has more files than were read. */
+  readonly truncated: boolean;
+}
+
 /**
  * Opaque strings, compared only against one another, where the empty string is the answer for a
  * file the change request deletes rather than a gap. A path is absent only where the read could
@@ -408,6 +418,11 @@ export interface PullRequestProviderApi {
     input: ProviderRepositoryRef & { readonly number: number },
   ) => Effect.Effect<ProviderFilesViewed, PullRequestProviderError>;
 
+  /** Line counts for every changed file. Optional: a host without one shows no breakdown. */
+  readonly getFileStats?: (
+    input: ProviderRepositoryRef & { readonly number: number },
+  ) => Effect.Effect<ProviderFileStats, PullRequestProviderError>;
+
   /**
    * A host with no bulk form is still owed one round trip for the batch rather than one per
    * file, since the point of gathering presses is that the host is asked once.
diff --git a/packages/source-control-github/src/server/GitHubPullRequestApi.ts b/packages/source-control-github/src/server/GitHubPullRequestApi.ts
index 0833d2d43397..c25699714d14 100644
--- a/packages/source-control-github/src/server/GitHubPullRequestApi.ts
+++ b/packages/source-control-github/src/server/GitHubPullRequestApi.ts
@@ -59,6 +59,7 @@ import {
   pullRequestChecksFromContexts,
   decodeWorkflowRunsJson,
   type GitHubPullRequestCore,
+  type GitHubPullRequestFileStat,
   type GitHubPullRequestWatchFingerprint,
   isSubjectOfPullRequest,
   LenientPullRequestList,
@@ -71,6 +72,7 @@ import {
   toPullRequestCheckContextsPage,
   toPullRequestCore,
   toPullRequestFilesViewedPage,
+  toPullRequestFileStatsPage,
   toPullRequestHeads,
   toPullRequestNodeId,
   toPullRequestPreview,
@@ -412,6 +414,11 @@ export interface GitHubPullRequestFilesViewed {
   readonly truncated: boolean;
 }
 
+export interface GitHubPullRequestFileStats {
+  readonly files: ReadonlyArray<GitHubPullRequestFileStat>;
+  readonly truncated: boolean;
+}
+
 export class GitHubPullRequestApi extends Context.Service<
   GitHubPullRequestApi,
   {
@@ -562,6 +569,13 @@ export class GitHubPullRequestApi extends Context.Service<
       readonly number: number;
     }) => Effect.Effect<GitHubPullRequestFilesViewed, GitHubPullRequestApiError>;
 
+    readonly getPullRequestFileStats: (input: {
+      readonly cwd: string;
+      readonly repository: string;
+      readonly host: string;
+      readonly number: number;
+    }) => Effect.Effect<GitHubPullRequestFileStats, GitHubPullRequestApiError>;
+
     /**
      * GitHub takes a single path per mutation, so a burst is batched with aliases into one
      * document rather than one subprocess per press.
@@ -2666,6 +2680,34 @@ export const make = Effect.gen(function* () {
       );
     },
 
+    getPullRequestFileStats: (input) => {
+      const { owner, name } = parseRepositorySelector(input.repository);
+      const target = { ...input, operation: "getPullRequestFileStats" };
+      return readPages(
+        GraphQLClient.pages(client.PullRequestFileStats, {
+          variables: { owner, name, number: input.number },
+          connection: (result) => {
+            const page = toPullRequestFileStatsPage(result);
+            return {
+              ...page,
+              pageInfo: { hasNextPage: page.nextCursor !== null, endCursor: page.nextCursor },
+            };
+          },
+        }),
+        {
+          ...target,
+          maxPages: FILES_VIEWED_MAX_PAGES,
+          hasNextPage: (page) => page.nextCursor !== null,
+        },
+      ).pipe(
+        graphql(target),
+        Effect.map(({ pages, truncated }) => ({
+          files: pages.flatMap((page) => page.files),
+          truncated,
+        })),
+      );
+    },
+
     setPullRequestFilesViewed: (input) => {
       if (input.files.length === 0) return Effect.void;
       const target = { ...input, operation: "setPullRequestFilesViewed" };
diff --git a/packages/source-control-github/src/server/GitHubPullRequestProvider.ts b/packages/source-control-github/src/server/GitHubPullRequestProvider.ts
index ad1a8fa68d96..dd710dffcfd6 100644
--- a/packages/source-control-github/src/server/GitHubPullRequestProvider.ts
+++ b/packages/source-control-github/src/server/GitHubPullRequestProvider.ts
@@ -524,6 +524,8 @@ export const make = Effect.gen(function* () {
     getFilesViewed: (input) =>
       cli.getPullRequestFilesViewed(input).pipe(Effect.mapError(fail("getFilesViewed"))),
 
+    getFileStats: (input) =>
+      cli.getPullRequestFileStats(input).pipe(Effect.mapError(fail("getFileStats"))),
     setFilesViewed: (input) =>
       cli.setPullRequestFilesViewed(input).pipe(Effect.mapError(fail("setFilesViewed"))),
 
diff --git a/packages/source-control-github/src/server/gitHubPullRequestJson.ts b/packages/source-control-github/src/server/gitHubPullRequestJson.ts
index 90bf0f5be04e..318ba41468c3 100644
--- a/packages/source-control-github/src/server/gitHubPullRequestJson.ts
+++ b/packages/source-control-github/src/server/gitHubPullRequestJson.ts
@@ -56,6 +56,7 @@ import type {
   PullRequestCheckContexts,
   PullRequestCore,
   PullRequestFilesViewed,
+  PullRequestFileStats,
   PullRequestHeads,
   PullRequestPreview as PullRequestPreviewQuery,
   PullRequestSubject,
@@ -1806,6 +1807,29 @@ export function toPullRequestFilesViewedPage(
   };
 }
 
+export interface GitHubPullRequestFileStat {
+  readonly path: string;
+  readonly additions: number;
+  readonly deletions: number;
+}
+
+export interface GitHubPullRequestFileStatsPage {
+  readonly files: ReadonlyArray<GitHubPullRequestFileStat>;
+  readonly nextCursor: string | null;
+}
+
+export function toPullRequestFileStatsPage(
+  result: PullRequestFileStats.Result,
+): GitHubPullRequestFileStatsPage {
+  const files = result.repository?.pullRequest?.files;
+  return {
+    files: nodesOf(files).flatMap(({ path, additions, deletions }) =>
+      path.length === 0 ? [] : [{ path, additions, deletions }],
+    ),
+    nextCursor: nextCursorOf(files?.pageInfo),
+  };
+}
+
 const RawStackPullRequestSchema = Schema.Struct({
   title: Schema.optional(Schema.String),
   draft: Schema.optional(Schema.Boolean),
diff --git a/packages/source-control-github/src/server/pullRequestReads.graphql b/packages/source-control-github/src/server/pullRequestReads.graphql
index da3778d6af82..7281af8c898a 100644
--- a/packages/source-control-github/src/server/pullRequestReads.graphql
+++ b/packages/source-control-github/src/server/pullRequestReads.graphql
@@ -475,6 +475,24 @@ query PullRequestFilesViewed($owner: String!, $name: String!, $number: Int!, $af
   }
 }
 
+query PullRequestFileStats($owner: String!, $name: String!, $number: Int!, $after: String) {
+  repository(owner: $owner, name: $name) {
+    pullRequest(number: $number) {
+      files(first: 100, after: $after) {
+        pageInfo {
+          hasNextPage
+          endCursor
+        }
+        nodes {
+          path
+          additions
+          deletions
+        }
+      }
+    }
+  }
+}
+
 # What a merge that rewrites its message reads first: GitHub's own message for the method, and
 # whether a merge queue will choose its own instead.
 query PullRequestMergeMessage(
diff --git a/packages/source-control-github/src/server/pullRequestReads.graphql.ts b/packages/source-control-github/src/server/pullRequestReads.graphql.ts
index bbf591bb6412..fd0fef547ea9 100644
--- a/packages/source-control-github/src/server/pullRequestReads.graphql.ts
+++ b/packages/source-control-github/src/server/pullRequestReads.graphql.ts
@@ -1237,27 +1237,27 @@ export declare namespace LabelCandidates {
 }
 
 /** A file changed in a pull request. */
-export const PullRequestChangedFile = Schema.Struct({
+export const PullRequestFilesViewedRepositoryPullRequestFilesNodesPullRequestChangedFile = Schema.Struct({
   /** The path of the file. */
   path: Schema.String,
   /** The state of the file for the viewer. */
   viewerViewedState: GraphQL.enumLiterals(Shared.FileViewedState.literals)
 })
-export interface PullRequestChangedFile extends Schema.Struct.Type<typeof PullRequestChangedFile.fields> {}
+export interface PullRequestFilesViewedRepositoryPullRequestFilesNodesPullRequestChangedFile extends Schema.Struct.Type<typeof PullRequestFilesViewedRepositoryPullRequestFilesNodesPullRequestChangedFile.fields> {}
 
 /** The connection type for PullRequestChangedFile. */
-export const PullRequestChangedFileConnection = Schema.Struct({
+export const PullRequestFilesViewedRepositoryPullRequestFilesPullRequestChangedFileConnection = Schema.Struct({
   /** Information to aid in pagination. */
   pageInfo: PullRequestCheckContextsRepositoryPullRequestCommitsNodesCommitStatusCheckRollupContextsPageInfoPageInfo,
   /** A list of nodes. */
-  nodes: Schema.NullOr(Schema.Array(Schema.NullOr(PullRequestChangedFile)))
+  nodes: Schema.NullOr(Schema.Array(Schema.NullOr(PullRequestFilesViewedRepositoryPullRequestFilesNodesPullRequestChangedFile)))
 })
-export interface PullRequestChangedFileConnection extends Schema.Struct.Type<typeof PullRequestChangedFileConnection.fields> {}
+export interface PullRequestFilesViewedRepositoryPullRequestFilesPullRequestChangedFileConnection extends Schema.Struct.Type<typeof PullRequestFilesViewedRepositoryPullRequestFilesPullRequestChangedFileConnection.fields> {}
 
 /** A repository pull request. */
 export const PullRequestFilesViewedRepositoryPullRequestPullRequest = Schema.Struct({
   /** Lists the files changed within this pull request. */
-  files: Schema.NullOr(PullRequestChangedFileConnection)
+  files: Schema.NullOr(PullRequestFilesViewedRepositoryPullRequestFilesPullRequestChangedFileConnection)
 })
 export interface PullRequestFilesViewedRepositoryPullRequestPullRequest extends Schema.Struct.Type<typeof PullRequestFilesViewedRepositoryPullRequestPullRequest.fields> {}
 
@@ -1298,6 +1298,70 @@ export declare namespace PullRequestFilesViewed {
   export type Result = typeof PullRequestFilesViewed.result.Type
 }
 
+/** A file changed in a pull request. */
+export const PullRequestFileStatsRepositoryPullRequestFilesNodesPullRequestChangedFile = Schema.Struct({
+  /** The path of the file. */
+  path: Schema.String,
+  /** The number of additions to the file. */
+  additions: Shared.Int,
+  /** The number of deletions to the file. */
+  deletions: Shared.Int
+})
+export interface PullRequestFileStatsRepositoryPullRequestFilesNodesPullRequestChangedFile extends Schema.Struct.Type<typeof PullRequestFileStatsRepositoryPullRequestFilesNodesPullRequestChangedFile.fields> {}
+
+/** The connection type for PullRequestChangedFile. */
+export const PullRequestFileStatsRepositoryPullRequestFilesPullRequestChangedFileConnection = Schema.Struct({
+  /** Information to aid in pagination. */
+  pageInfo: PullRequestCheckContextsRepositoryPullRequestCommitsNodesCommitStatusCheckRollupContextsPageInfoPageInfo,
+  /** A list of nodes. */
+  nodes: Schema.NullOr(Schema.Array(Schema.NullOr(PullRequestFileStatsRepositoryPullRequestFilesNodesPullRequestChangedFile)))
+})
+export interface PullRequestFileStatsRepositoryPullRequestFilesPullRequestChangedFileConnection extends Schema.Struct.Type<typeof PullRequestFileStatsRepositoryPullRequestFilesPullRequestChangedFileConnection.fields> {}
+
+/** A repository pull request. */
+export const PullRequestFileStatsRepositoryPullRequestPullRequest = Schema.Struct({
+  /** Lists the files changed within this pull request. */
+  files: Schema.NullOr(PullRequestFileStatsRepositoryPullRequestFilesPullRequestChangedFileConnection)
+})
+export interface PullRequestFileStatsRepositoryPullRequestPullRequest extends Schema.Struct.Type<typeof PullRequestFileStatsRepositoryPullRequestPullRequest.fields> {}
+
+/** A repository contains the content for a project. */
+export const PullRequestFileStatsRepositoryRepository = Schema.Struct({
+  /** Returns a single pull request from the current repository by number. */
+  pullRequest: Schema.NullOr(PullRequestFileStatsRepositoryPullRequestPullRequest)
+})
+export interface PullRequestFileStatsRepositoryRepository extends Schema.Struct.Type<typeof PullRequestFileStatsRepositoryRepository.fields> {}
+
+/** `query PullRequestFileStats` */
+export const PullRequestFileStats = GraphQL.query("PullRequestFileStats", {
+  document: {
+    variables: [
+      { name: "owner", body: "String!" },
+      { name: "name", body: "String!" },
+      { name: "number", body: "Int!" },
+      { name: "after", body: "String" }
+    ],
+    selections: [
+      { name: "repository", body: ["(owner:$", "owner", " name:$", "name", "){pullRequest(number:$", "number", "){files(first:100 after:$", "after", "){pageInfo{hasNextPage endCursor}nodes{path additions deletions}}}}"] }
+    ],
+    fragments: []
+  },
+  variables: {
+    owner: Schema.String,
+    name: Schema.String,
+    number: Shared.Int,
+    after: Schema.optional(Schema.NullOr(Schema.String))
+  },
+  result: Schema.Struct({
+    /** Lookup a given repository by the owner and repository name. */
+    repository: Schema.NullOr(PullRequestFileStatsRepositoryRepository)
+  })
+})
+export declare namespace PullRequestFileStats {
+  export type Variables = typeof PullRequestFileStats.variables.Type
+  export type Result = typeof PullRequestFileStats.result.Type
+}
+
 /** A repository pull request. */
 export const PullRequestMergeMessageRepositoryPullRequestPullRequest = Schema.Struct({
   /** Indicates whether the pull request's base ref has a merge queue enabled. */
@@ -1523,4 +1587,4 @@ export declare namespace PullRequestSourceBranch {
 }
 
 /** Every operation in pullRequestReads.graphql. */
-export const PullRequestReadsGraphQLGroup = GraphQLGroup.make(RoutingIdentityViewer, ActorAvatars, PullRequestCore, PullRequestCheckContexts, PullRequestPreview, PullRequestActivity, PullRequestHeads, PullRequestNodeId, PullRequestSubject, ViewerPermissions, ReviewerCandidates, LabelCandidates, PullRequestFilesViewed, PullRequestMergeMessage, PullRequestActionState, PullRequestBranchToDelete, PullRequestSourceBranch)
+export const PullRequestReadsGraphQLGroup = GraphQLGroup.make(RoutingIdentityViewer, ActorAvatars, PullRequestCore, PullRequestCheckContexts, PullRequestPreview, PullRequestActivity, PullRequestHeads, PullRequestNodeId, PullRequestSubject, ViewerPermissions, ReviewerCandidates, LabelCandidates, PullRequestFilesViewed, PullRequestFileStats, PullRequestMergeMessage, PullRequestActionState, PullRequestBranchToDelete, PullRequestSourceBranch)