diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8c7357c..4ea13e3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,20 @@ All notable changes to the AnchorNet API are documented here.
 
 [Unreleased]
 Added
+Security: the metrics endpoints (GET /api/v1/metrics and
+/api/v1/metrics/history) are now protected reads. When API_KEY or the new
+METRICS_API_KEY is configured they require a matching x-api-key header
+(401 otherwise); when neither is set they stay open, matching the existing
+write-auth model. METRICS_API_KEY is a read-only credential that unlocks
+metrics but not mutating routes, so a monitoring scraper needs no write
+key. Metrics reads are now rate-limited per client (METRICS_RATE_LIMIT_MAX,
+default 120/min) via a new opt-in limitReads flag on the rate limiter, so
+the history endpoint cannot be used as an unlimited load generator.
+Snapshot-history retention remains bounded to the most recent 50 entries,
+now pinned by a route-level test. src/openapi.ts declares an ApiKeyAuth
+security scheme and marks both metrics operations as protected. The
+read-limiting is scoped to the metrics mount; global read limiting and a
+shared multi-instance store remain owned by the separate rate-limiter issue.
 Metrics: GET /api/v1/metrics now reports totalSettledAmount (sum of
 settlement amount) and totalFeesCollected (sum of settlement fee),
 computed from executed settlements only — pending settlements have
diff --git a/README.md b/README.md
index 7708c42..3de07f8 100644
--- a/README.md
+++ b/README.md
@@ -136,7 +136,33 @@ client-side. Each read also appends a timestamped snapshot to an in-memory
 rolling history (last 50 reads).
 GET /api/v1/metrics/history – the recorded metrics snapshots, oldest first
 ({ snapshots: [...] }); each snapshot carries the same fields as
-GET /api/v1/metrics plus an ISO-8601 timestamp
+GET /api/v1/metrics plus an ISO-8601 timestamp. Retention is bounded to the
+most recent 50 snapshots (MAX_HISTORY in src/routes/metrics.ts); older ones
+are evicted, so the response can never grow without limit.
+
+Metrics access (protected reads). Unlike the other read endpoints, the two
+metrics endpoints expose aggregate operational intelligence — participant
+counts, total liquidity, settlement volume and protocol fees earned, sampled
+over time. That is useful to an operator and equally useful to someone
+profiling the network before targeting it, so exposing it is treated as a
+deliberate decision rather than a middleware side effect:
+
+- When neither API_KEY nor METRICS_API_KEY is set, metrics reads are open
+  (unchanged local/dev behaviour).
+- When either key is set, GET /api/v1/metrics and GET /api/v1/metrics/history
+  require a matching x-api-key header and return 401 otherwise.
+- A monitoring scraper should be given METRICS_API_KEY — a read-only
+  credential accepted for metrics but not for any mutating route — so
+  monitoring keeps working without handing the write key to the scraper. The
+  primary API_KEY is also accepted for metrics, so an operator already holding
+  it needs nothing extra. Example scrape:
+  `curl -H "x-api-key: $METRICS_API_KEY" http://localhost:3001/api/v1/metrics`
+- Metrics reads (both endpoints) are rate-limited per client via
+  METRICS_RATE_LIMIT_MAX (default 120/min), so the history endpoint cannot be
+  used as a cheap load generator. This read-path limiting is scoped to the
+  metrics mount and owned by this change; extending rate limiting to all reads
+  and to a shared multi-instance store is tracked by the separate
+  rate-limiter issue.
 Errors use a uniform envelope: { "error": { "code", "message" } }, including
 malformed JSON (400) and oversized request bodies (413,
 PAYLOAD_TOO_LARGE). Every response carries an x-request-id header for
@@ -252,7 +278,10 @@ The application is configured using environment variables. Every environment var
 Variable Default Valid Range / Format Description
 PORT 3001 Positive integer (typically 1 - 65535) HTTP port the server binds to. Non-numeric values fall back to default.
 FEE_BPS 10 Integer between 0 and 10000 (inclusive) Protocol fee in basis points applied to settlements and quotes. The process throws an error and fails to start if configured outside this range.
-API_KEY (Unset) Any non-empty string If set, mutating requests (POST/PUT/PATCH/DELETE) must send an matching x-api-key header. Whitespace-only values are treated as unset.
+API_KEY (Unset) Any non-empty string If set, mutating requests (POST/PUT/PATCH/DELETE) must send an matching x-api-key header. Whitespace-only values are treated as unset. Also accepted for metrics reads.
+METRICS_API_KEY (Unset) Any non-empty string Read-only credential for the metrics endpoints. If either this or API_KEY is set, GET /api/v1/metrics and /history require a matching x-api-key header. This key unlocks metrics only — it cannot authorize mutating requests — so a monitoring scraper can read metrics without the write key. Whitespace-only values are treated as unset.
+METRICS_RATE_LIMIT_MAX 120 Positive integer Maximum metrics reads allowed per client within the metrics window. Covers reads (unlike the mutating-only global limiter) so the history endpoint is not an unlimited load generator.
+METRICS_RATE_LIMIT_WINDOW_MS 60000 (1 min) Positive integer Length of the rolling window for the metrics read rate limit.
 CORS_ORIGIN (Unset) Comma-separated list of origin URLs Allowed CORS origins. Whitespace around entries is trimmed; empty entries are ignored. If unset, every origin is permitted.
 BODY_LIMIT 100kb Express bytes-compatible string (e.g., "500kb", "2mb") Maximum accepted JSON request body size. Default is applied if value is blank.
 MAINTENANCE_MODE false "1", "true" (case-insensitive) to enable When enabled, mutating requests are rejected with a 503 Service Unavailable error, while read requests continue to function normally.
diff --git a/src/app.ts b/src/app.ts
index ef61c44..8452e58 100644
--- a/src/app.ts
+++ b/src/app.ts
@@ -25,6 +25,7 @@ import { errorHandler, notFoundHandler } from "./middleware/errorHandler";
 import { requestLogger } from "./middleware/requestLogger";
 import { requestId } from "./middleware/requestId";
 import { apiKeyAuth } from "./middleware/apiKeyAuth";
+import { metricsAuth } from "./middleware/metricsAuth";
 import { rateLimiter } from "./middleware/rateLimiter";
 import { securityHeaders } from "./middleware/securityHeaders";
 import { idempotency } from "./middleware/idempotency";
@@ -116,8 +117,24 @@ export function createApp(): Express {
   app.use("/api/v1/quote", quoteRouter(quotes));
   app.use("/api/v1/anchors", anchorRouter(anchors, settlements));
   app.use("/api/v1/settlements", settlementRouter(settlements, audit.entries));
+  // Metrics expose aggregate operational data (participant counts, liquidity
+  // totals, settlement volume and fees over time). That is deliberately
+  // treated as protected rather than public: reads require authentication
+  // whenever a key is configured, and — unlike the global writes-only limiter
+  // — are rate-limited via `limitReads` so the unauthenticated-or-not history
+  // endpoint cannot be used as a cheap load generator. When no key is set the
+  // guard is a no-op, preserving open access for local/dev deployments.
   app.use(
     "/api/v1/metrics",
+    metricsAuth(config.apiKey, config.metricsApiKey),
+    rateLimiter(
+      {
+        max: config.metricsRateLimitMax,
+        windowMs: config.metricsRateLimitWindowMs,
+        limitReads: true,
+      },
+      config.apiKey ?? config.metricsApiKey,
+    ),
     metricsRouter({
       liquidity,
       anchors,
diff --git a/src/config.test.ts b/src/config.test.ts
index 1881b7b..035392e 100644
--- a/src/config.test.ts
+++ b/src/config.test.ts
@@ -150,6 +150,35 @@ describe("loadConfig", () => {
     expect(config.rateLimitWindowMs).toBe(120000);
   });
 
+  it("leaves the metrics API key unset by default", () => {
+    expect(loadConfig({}).metricsApiKey).toBeUndefined();
+  });
+
+  it("reads a configured metrics API key", () => {
+    expect(loadConfig({ METRICS_API_KEY: "scraper" }).metricsApiKey).toBe(
+      "scraper",
+    );
+  });
+
+  it("treats a blank metrics API key as unset", () => {
+    expect(loadConfig({ METRICS_API_KEY: "   " }).metricsApiKey).toBeUndefined();
+  });
+
+  it("defaults the metrics read rate limit", () => {
+    const config = loadConfig({});
+    expect(config.metricsRateLimitMax).toBe(120);
+    expect(config.metricsRateLimitWindowMs).toBe(60_000);
+  });
+
+  it("reads the metrics read rate limit from the environment", () => {
+    const config = loadConfig({
+      METRICS_RATE_LIMIT_MAX: "10",
+      METRICS_RATE_LIMIT_WINDOW_MS: "5000",
+    });
+    expect(config.metricsRateLimitMax).toBe(10);
+    expect(config.metricsRateLimitWindowMs).toBe(5000);
+  });
+
   describe("TRUST_PROXY", () => {
     it('parses "true" to boolean true', () => {
       expect(loadConfig({ TRUST_PROXY: "true" }).trustProxy).toBe(true);
diff --git a/src/config.ts b/src/config.ts
index 0e34d77..237f989 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -11,6 +11,14 @@ export interface Config {
   feeBps: number;
   /** Optional API key required for mutating requests (disabled if unset). */
   apiKey?: string;
+  /**
+   * Optional read-only credential that grants access to the metrics endpoints
+   * (`GET /api/v1/metrics` and `/history`) without granting the write access
+   * carried by {@link apiKey}. Lets a monitoring scraper read operational
+   * metrics with a credential that cannot mutate the network. Whitespace-only
+   * values are treated as unset.
+   */
+  metricsApiKey?: string;
   /**
    * Allowed CORS origins. `undefined` means no allowlist is configured and
    * every origin is permitted (the historical default behavior).
@@ -30,6 +38,15 @@ export interface Config {
   rateLimitMax: number;
   /** Length of the rolling window, in milliseconds. */
   rateLimitWindowMs: number;
+  /**
+   * Maximum metrics **reads** allowed per client within the metrics window.
+   * Unlike {@link rateLimitMax}, this budget covers the read-only metrics
+   * endpoints, which are otherwise unlimited. Defaults higher than the
+   * mutating limit so a polling scraper is not throttled.
+   */
+  metricsRateLimitMax: number;
+  /** Length of the metrics read rate-limiting window, in milliseconds. */
+  metricsRateLimitWindowMs: number;
   /**
    * Express `trust proxy` setting. When enabled behind a load balancer,
    * Express trusts the `X-Forwarded-For` header so `req.ip` reflects the
@@ -121,6 +138,7 @@ export function loadConfig(
   env: Record<string, string | undefined> = process.env,
 ): Config {
   const apiKey = env.API_KEY?.trim();
+  const metricsApiKey = env.METRICS_API_KEY?.trim();
   const feeBps = intFromEnv(env.FEE_BPS, 10);
 
   if (feeBps < MIN_FEE_BPS || feeBps > MAX_FEE_BPS) {
@@ -133,6 +151,7 @@ export function loadConfig(
     port: intFromEnv(env.PORT, 3001),
     feeBps,
     apiKey: apiKey ? apiKey : undefined,
+    metricsApiKey: metricsApiKey ? metricsApiKey : undefined,
     corsOrigins: parseCorsOrigins(env.CORS_ORIGIN),
     bodyLimit: env.BODY_LIMIT?.trim() || DEFAULT_BODY_LIMIT,
     maintenanceMode: parseBooleanFlag(env.MAINTENANCE_MODE),
@@ -143,6 +162,8 @@ export function loadConfig(
     idempotencyTtlMs: intFromEnv(env.IDEMPOTENCY_TTL_MS, 86_400_000),
     rateLimitMax: intFromEnv(env.RATE_LIMIT_MAX, 30),
     rateLimitWindowMs: intFromEnv(env.RATE_LIMIT_WINDOW_MS, 60_000),
+    metricsRateLimitMax: intFromEnv(env.METRICS_RATE_LIMIT_MAX, 120),
+    metricsRateLimitWindowMs: intFromEnv(env.METRICS_RATE_LIMIT_WINDOW_MS, 60_000),
     trustProxy: parseTrustProxy(env.TRUST_PROXY),
   };
 }
diff --git a/src/middleware/metricsAuth.test.ts b/src/middleware/metricsAuth.test.ts
new file mode 100644
index 0000000..cf7ea32
--- /dev/null
+++ b/src/middleware/metricsAuth.test.ts
@@ -0,0 +1,116 @@
+import request from "supertest";
+import { createApp } from "../app";
+
+/**
+ * Metrics reads are protected whenever a credential is configured. These tests
+ * exercise the three deployment shapes: open (no key), primary-key only, and a
+ * dedicated read-only metrics key alongside the write key.
+ */
+describe("metricsAuth", () => {
+  const originalApiKey = process.env.API_KEY;
+  const originalMetricsKey = process.env.METRICS_API_KEY;
+
+  afterEach(() => {
+    if (originalApiKey === undefined) delete process.env.API_KEY;
+    else process.env.API_KEY = originalApiKey;
+    if (originalMetricsKey === undefined) delete process.env.METRICS_API_KEY;
+    else process.env.METRICS_API_KEY = originalMetricsKey;
+  });
+
+  describe("open access when no key is configured", () => {
+    beforeEach(() => {
+      delete process.env.API_KEY;
+      delete process.env.METRICS_API_KEY;
+    });
+
+    it("serves current metrics without a key", async () => {
+      const res = await request(createApp()).get("/api/v1/metrics");
+      expect(res.status).toBe(200);
+    });
+
+    it("serves metrics history without a key", async () => {
+      const res = await request(createApp()).get("/api/v1/metrics/history");
+      expect(res.status).toBe(200);
+    });
+  });
+
+  describe("protected by the primary API key", () => {
+    beforeEach(() => {
+      process.env.API_KEY = "write-secret";
+      delete process.env.METRICS_API_KEY;
+    });
+
+    it("rejects metrics reads without a key", async () => {
+      const res = await request(createApp()).get("/api/v1/metrics");
+      expect(res.status).toBe(401);
+      expect(res.body.error.code).toBe("UNAUTHORIZED");
+    });
+
+    it("rejects history reads without a key", async () => {
+      const res = await request(createApp()).get("/api/v1/metrics/history");
+      expect(res.status).toBe(401);
+    });
+
+    it("rejects metrics reads with the wrong key", async () => {
+      const res = await request(createApp())
+        .get("/api/v1/metrics")
+        .set("x-api-key", "nope");
+      expect(res.status).toBe(401);
+    });
+
+    it("allows metrics reads with the primary key", async () => {
+      const res = await request(createApp())
+        .get("/api/v1/metrics")
+        .set("x-api-key", "write-secret");
+      expect(res.status).toBe(200);
+      expect(res.body.anchors).toBe(0);
+    });
+
+    it("does not trigger a snapshot when a read is rejected", async () => {
+      const app = createApp();
+      // Rejected read must not leak data via the history side effect.
+      await request(app).get("/api/v1/metrics");
+      const res = await request(app)
+        .get("/api/v1/metrics/history")
+        .set("x-api-key", "write-secret");
+      expect(res.status).toBe(200);
+      expect(res.body.snapshots).toEqual([]);
+    });
+  });
+
+  describe("dedicated read-only metrics key", () => {
+    beforeEach(() => {
+      process.env.API_KEY = "write-secret";
+      process.env.METRICS_API_KEY = "read-only-scraper";
+    });
+
+    it("allows metrics reads with the read-only metrics key", async () => {
+      const res = await request(createApp())
+        .get("/api/v1/metrics")
+        .set("x-api-key", "read-only-scraper");
+      expect(res.status).toBe(200);
+    });
+
+    it("still allows metrics reads with the primary key", async () => {
+      const res = await request(createApp())
+        .get("/api/v1/metrics")
+        .set("x-api-key", "write-secret");
+      expect(res.status).toBe(200);
+    });
+
+    it("does not let the read-only metrics key authorize writes", async () => {
+      const res = await request(createApp())
+        .post("/api/v1/anchors")
+        .set("x-api-key", "read-only-scraper")
+        .send({ id: "anchorA" });
+      expect(res.status).toBe(401);
+    });
+
+    it("rejects an unknown key", async () => {
+      const res = await request(createApp())
+        .get("/api/v1/metrics/history")
+        .set("x-api-key", "guessed");
+      expect(res.status).toBe(401);
+    });
+  });
+});
diff --git a/src/middleware/metricsAuth.ts b/src/middleware/metricsAuth.ts
new file mode 100644
index 0000000..2fc507c
--- /dev/null
+++ b/src/middleware/metricsAuth.ts
@@ -0,0 +1,56 @@
+/**
+ * Read authentication for the metrics endpoints.
+ *
+ * The aggregate metrics served by `GET /api/v1/metrics` and
+ * `GET /api/v1/metrics/history` — anchor and participant counts, total
+ * liquidity, settlement volume and protocol fees earned, sampled over time —
+ * describe the operational state of the network. That is business
+ * intelligence: valuable to an operator, and equally valuable to someone
+ * profiling the network before targeting it. Exposing it publicly should be a
+ * deliberate decision, not a side effect of the write-only `apiKeyAuth`. This
+ * middleware makes metrics reads authenticated by default.
+ *
+ * A request is authorized when it presents an `x-api-key` header matching
+ * **either**:
+ *   - the primary {@link apiKey} (the same credential that authorizes writes),
+ *     so an operator already holding it needs nothing new; or
+ *   - a dedicated, read-only {@link metricsApiKey}, so a monitoring scraper can
+ *     read metrics with a credential that cannot mutate the network.
+ *
+ * When neither key is configured the middleware is a no-op (open access),
+ * matching the "locked only once a key is set" model of `apiKeyAuth` and
+ * preserving the historical behaviour for local development and deliberately
+ * open deployments.
+ */
+
+import { NextFunction, Request, Response } from "express";
+import { ApiError } from "../errors/ApiError";
+
+/**
+ * Builds the metrics read-authentication middleware.
+ *
+ * @param apiKey        Primary API key, if configured. Accepted for metrics
+ *                      reads so operators reuse a single credential.
+ * @param metricsApiKey Dedicated read-only metrics key, if configured.
+ */
+export function metricsAuth(apiKey?: string, metricsApiKey?: string) {
+  return (req: Request, _res: Response, next: NextFunction): void => {
+    // No credential configured anywhere: metrics remain openly readable.
+    if (!apiKey && !metricsApiKey) {
+      next();
+      return;
+    }
+
+    const presented = req.header("x-api-key");
+    const matchesPrimary = apiKey !== undefined && presented === apiKey;
+    const matchesMetrics =
+      metricsApiKey !== undefined && presented === metricsApiKey;
+
+    if (matchesPrimary || matchesMetrics) {
+      next();
+      return;
+    }
+
+    next(ApiError.unauthorized("missing or invalid API key"));
+  };
+}
diff --git a/src/middleware/rateLimiter.ts b/src/middleware/rateLimiter.ts
index 6b25d14..64de864 100644
--- a/src/middleware/rateLimiter.ts
+++ b/src/middleware/rateLimiter.ts
@@ -41,6 +41,18 @@ export interface RateLimitOptions {
    * require the exclusion list to account for the mount prefix.
    */
   skipPaths?: string[];
+  /**
+   * When `true`, this limiter also counts read (non-mutating) requests toward
+   * the per-client budget. Defaults `false`, so the global limiter's
+   * writes-only behaviour is unchanged.
+   *
+   * This flag is enabled only for the metrics mount, whose read endpoints
+   * (notably `GET /history`) are otherwise unlimited. Extending read limiting
+   * to every route — and the shared, multi-instance store that would require —
+   * is deliberately left to the separate rate-limiter issue; this PR owns the
+   * flag and its use for metrics only.
+   */
+  limitReads?: boolean;
 }
 
 export function rateLimiter(
@@ -52,7 +64,7 @@ export function rateLimiter(
   const buckets = new Map<string, Bucket>();
 
   return (req: Request, _res: Response, next: NextFunction): void => {
-    if (!MUTATING_METHODS.has(req.method)) {
+    if (!MUTATING_METHODS.has(req.method) && !options.limitReads) {
       next();
       return;
     }
diff --git a/src/openapi.test.ts b/src/openapi.test.ts
index 936c76e..3236a3c 100644
--- a/src/openapi.test.ts
+++ b/src/openapi.test.ts
@@ -52,6 +52,35 @@ describe("openapi spec", () => {
     expect(history.description).toContain("totalFeesCollected");
   });
 
+  it("declares the x-api-key security scheme and marks metrics as protected", () => {
+    const spec = buildOpenApiSpec() as {
+      components?: {
+        securitySchemes?: Record<
+          string,
+          { type?: string; in?: string; name?: string }
+        >;
+      };
+      paths: Record<string, { get: { security?: unknown[]; description?: string } }>;
+    };
+
+    const scheme = spec.components?.securitySchemes?.ApiKeyAuth;
+    expect(scheme).toMatchObject({
+      type: "apiKey",
+      in: "header",
+      name: "x-api-key",
+    });
+
+    expect(spec.paths["/api/v1/metrics"].get.security).toEqual([
+      { ApiKeyAuth: [] },
+    ]);
+    expect(spec.paths["/api/v1/metrics/history"].get.security).toEqual([
+      { ApiKeyAuth: [] },
+    ]);
+    expect(spec.paths["/api/v1/metrics/history"].get.description).toContain(
+      "50",
+    );
+  });
+
   it("documents the dryRun preflight parameter on POST /api/v1/anchors/bulk", () => {
     const spec = buildOpenApiSpec() as {
       paths: Record<
diff --git a/src/openapi.ts b/src/openapi.ts
index f4b50b4..64e65df 100644
--- a/src/openapi.ts
+++ b/src/openapi.ts
@@ -17,6 +17,19 @@ export function buildOpenApiSpec(): Record<string, unknown> {
       version: PKG_VERSION,
       description: "Liquidity coordination network for Stellar anchors",
     },
+    components: {
+      securitySchemes: {
+        // Sent as the `x-api-key` request header. The same scheme carries both
+        // the primary write key (`API_KEY`) and the dedicated read-only metrics
+        // key (`METRICS_API_KEY`); which credential is required depends on the
+        // operation.
+        ApiKeyAuth: {
+          type: "apiKey",
+          in: "header",
+          name: "x-api-key",
+        },
+      },
+    },
     paths: {
       "/health": {
         get: { summary: "Health check" },
@@ -200,7 +213,12 @@ export function buildOpenApiSpec(): Record<string, unknown> {
             "totalFeesCollected (sum of settlement fee). Both value totals are computed " +
             "from executed settlements only — pending settlements have merely reserved " +
             "liquidity and cancelled ones never moved value, so neither contributes. " +
-            "Each read also appends a timestamped snapshot to the rolling history.",
+            "Each read also appends a timestamped snapshot to the rolling history. " +
+            "Protected: when API_KEY or METRICS_API_KEY is configured, callers must " +
+            "send a matching x-api-key header (a read-only METRICS_API_KEY is accepted " +
+            "so a scraper never needs the write key); requests are also rate-limited. " +
+            "When no key is set the endpoint is open, matching the write-auth model.",
+          security: [{ ApiKeyAuth: [] }],
         },
       },
       "/api/v1/metrics/history": {
@@ -209,7 +227,10 @@ export function buildOpenApiSpec(): Record<string, unknown> {
           description:
             "Returns { snapshots: [...] }, where each snapshot carries the same fields as " +
             "GET /api/v1/metrics (including totalSettledAmount and totalFeesCollected) " +
-            "plus an ISO-8601 timestamp.",
+            "plus an ISO-8601 timestamp. Retention is bounded to the most recent 50 " +
+            "snapshots (older ones are evicted). Same authentication and rate limiting " +
+            "as GET /api/v1/metrics.",
+          security: [{ ApiKeyAuth: [] }],
         },
       },
     },
diff --git a/src/routes/metrics.test.ts b/src/routes/metrics.test.ts
index 2157124..544a0c0 100644
--- a/src/routes/metrics.test.ts
+++ b/src/routes/metrics.test.ts
@@ -198,6 +198,85 @@ describe("metrics route", () => {
   });
 });
 
+describe("metrics history retention", () => {
+  it("caps the retained snapshot history at 50 entries", async () => {
+    const app = createApp();
+    await seed(app);
+
+    // Each read of the current metrics appends one snapshot. Drive well past
+    // the MAX_HISTORY = 50 bound to prove the oldest entries are evicted
+    // rather than accumulating without limit.
+    for (let i = 0; i < 60; i += 1) {
+      await request(app).get("/api/v1/metrics");
+    }
+
+    const res = await request(app).get("/api/v1/metrics/history");
+    expect(res.status).toBe(200);
+    expect(res.body.snapshots).toHaveLength(50);
+  });
+
+  it("retains the most recent snapshots, dropping the oldest", async () => {
+    jest.useFakeTimers();
+    try {
+      const app = createApp();
+      await seed(app);
+
+      // Take 51 snapshots at distinct, strictly increasing timestamps so the
+      // very first one is the single entry that must be evicted at cap.
+      for (let i = 0; i < 51; i += 1) {
+        jest.setSystemTime(new Date(2026, 0, 1, 0, 0, i));
+        await request(app).get("/api/v1/metrics");
+      }
+
+      const res = await request(app).get("/api/v1/metrics/history");
+      expect(res.body.snapshots).toHaveLength(50);
+      // The oldest (second 0) is gone; the window now starts at second 1.
+      expect(res.body.snapshots[0].timestamp).toBe(
+        new Date(2026, 0, 1, 0, 0, 1).toISOString(),
+      );
+      expect(res.body.snapshots[49].timestamp).toBe(
+        new Date(2026, 0, 1, 0, 0, 50).toISOString(),
+      );
+    } finally {
+      jest.useRealTimers();
+    }
+  });
+});
+
+describe("metrics read rate limiting", () => {
+  const original = process.env.METRICS_RATE_LIMIT_MAX;
+
+  afterEach(() => {
+    if (original === undefined) delete process.env.METRICS_RATE_LIMIT_MAX;
+    else process.env.METRICS_RATE_LIMIT_MAX = original;
+  });
+
+  it("rejects metrics reads over the per-client budget with 429", async () => {
+    process.env.METRICS_RATE_LIMIT_MAX = "3";
+    const app = createApp();
+
+    for (let i = 0; i < 3; i += 1) {
+      const ok = await request(app).get("/api/v1/metrics");
+      expect(ok.status).toBe(200);
+    }
+
+    const blocked = await request(app).get("/api/v1/metrics");
+    expect(blocked.status).toBe(429);
+    expect(blocked.body.error.code).toBe("RATE_LIMITED");
+  });
+
+  it("counts history reads against the same read budget", async () => {
+    process.env.METRICS_RATE_LIMIT_MAX = "2";
+    const app = createApp();
+
+    expect((await request(app).get("/api/v1/metrics")).status).toBe(200);
+    expect((await request(app).get("/api/v1/metrics/history")).status).toBe(200);
+
+    const blocked = await request(app).get("/api/v1/metrics/history");
+    expect(blocked.status).toBe(429);
+  });
+});
+
 describe("metrics settled-value totals", () => {
   it("reports zero settled amount and fees on a fresh app", async () => {
     const res = await request(createApp()).get("/api/v1/metrics");