diff --git a/packages/core-shared/src/instrumentation/otel/otel-metrics.test.ts b/packages/core-shared/src/instrumentation/otel/otel-metrics.test.ts
new file mode 100644
index 0000000..a143803
--- /dev/null
+++ b/packages/core-shared/src/instrumentation/otel/otel-metrics.test.ts
@@ -0,0 +1,120 @@
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { metrics } from "@opentelemetry/api";
+import {
+  InMemoryMetricExporter,
+  MeterProvider,
+  PeriodicExportingMetricReader,
+  AggregationTemporality,
+} from "@opentelemetry/sdk-metrics";
+import { OtelMetrics } from "./otel-metrics";
+
+function setupMeterProvider(): {
+  exporter: InMemoryMetricExporter;
+  provider: MeterProvider;
+} {
+  const exporter = new InMemoryMetricExporter(AggregationTemporality.CUMULATIVE);
+  const reader = new PeriodicExportingMetricReader({
+    exporter,
+    exportIntervalMillis: 100,
+  });
+  const provider = new MeterProvider({ readers: [reader] });
+  metrics.setGlobalMeterProvider(provider);
+  return { exporter, provider };
+}
+
+describe("OtelMetrics", () => {
+  let exporter: InMemoryMetricExporter;
+  let provider: MeterProvider;
+
+  beforeEach(() => {
+    ({ exporter, provider } = setupMeterProvider());
+  });
+
+  afterEach(async () => {
+    await provider.shutdown();
+    metrics.disable();
+  });
+
+  it("counter() records a counter measurement", async () => {
+    const otelMetrics = new OtelMetrics();
+    otelMetrics.counter("http.requests", 1, { method: "GET" });
+
+    await provider.forceFlush();
+    const metrics_ = exporter.getMetrics();
+    const counterMetric = metrics_
+      .flatMap((rm) => rm.scopeMetrics)
+      .flatMap((sm) => sm.metrics)
+      .find((m) => m.descriptor.name === "http.requests");
+
+    expect(counterMetric).toBeDefined();
+    expect(counterMetric!.dataPoints).toHaveLength(1);
+    expect(counterMetric!.dataPoints[0]!.value).toBe(1);
+  });
+
+  it("counter() defaults value to 1 when omitted", async () => {
+    const otelMetrics = new OtelMetrics();
+    otelMetrics.counter("events.processed");
+
+    await provider.forceFlush();
+    const metrics_ = exporter.getMetrics();
+    const counterMetric = metrics_
+      .flatMap((rm) => rm.scopeMetrics)
+      .flatMap((sm) => sm.metrics)
+      .find((m) => m.descriptor.name === "events.processed");
+
+    expect(counterMetric).toBeDefined();
+    expect(counterMetric!.dataPoints[0]!.value).toBe(1);
+  });
+
+  it("histogram() records a histogram measurement", async () => {
+    const otelMetrics = new OtelMetrics();
+    otelMetrics.histogram("http.duration", 250, { route: "/api/me" });
+
+    await provider.forceFlush();
+    const metrics_ = exporter.getMetrics();
+    const histogramMetric = metrics_
+      .flatMap((rm) => rm.scopeMetrics)
+      .flatMap((sm) => sm.metrics)
+      .find((m) => m.descriptor.name === "http.duration");
+
+    expect(histogramMetric).toBeDefined();
+    expect(histogramMetric!.dataPoints).toHaveLength(1);
+    // Histogram data points carry a Histogram aggregate value with sum/count/buckets.
+    const dp = histogramMetric!.dataPoints[0] as {
+      value: { sum?: number; count: number };
+    };
+    expect(dp.value.sum).toBe(250);
+    expect(dp.value.count).toBe(1);
+  });
+
+  it("gauge() records via UpDownCounter", async () => {
+    const otelMetrics = new OtelMetrics();
+    otelMetrics.gauge("queue.depth", 5, { queue: "emails" });
+
+    await provider.forceFlush();
+    const metrics_ = exporter.getMetrics();
+    const gaugeMetric = metrics_
+      .flatMap((rm) => rm.scopeMetrics)
+      .flatMap((sm) => sm.metrics)
+      .find((m) => m.descriptor.name === "queue.depth");
+
+    expect(gaugeMetric).toBeDefined();
+    expect(gaugeMetric!.dataPoints).toHaveLength(1);
+  });
+
+  it("lazily caches instrument instances — same counter object reused across calls", async () => {
+    const otelMetrics = new OtelMetrics();
+    otelMetrics.counter("reuse.test", 1);
+    otelMetrics.counter("reuse.test", 2);
+
+    await provider.forceFlush();
+    const metrics_ = exporter.getMetrics();
+    const counterMetric = metrics_
+      .flatMap((rm) => rm.scopeMetrics)
+      .flatMap((sm) => sm.metrics)
+      .find((m) => m.descriptor.name === "reuse.test");
+
+    // Cumulative: should accumulate both adds (1+2=3)
+    expect(counterMetric!.dataPoints[0]!.value).toBe(3);
+  });
+});
diff --git a/packages/core-shared/src/instrumentation/otel/otel-metrics.ts b/packages/core-shared/src/instrumentation/otel/otel-metrics.ts
new file mode 100644
index 0000000..5cb5f2d
--- /dev/null
+++ b/packages/core-shared/src/instrumentation/otel/otel-metrics.ts
@@ -0,0 +1,70 @@
+import { metrics } from "@opentelemetry/api";
+import type { Counter, Histogram, UpDownCounter } from "@opentelemetry/api";
+import type { IMetrics, MetricAttributeValue } from "../metrics.interface";
+
+/**
+ * OTel-backed IMetrics implementation.
+ *
+ * - counter   → OTel Counter (monotonic, add-only)
+ * - histogram → OTel Histogram
+ * - gauge     → OTel UpDownCounter (synchronous emit). Known limitation: this
+ *               accumulates deltas, not point-in-time values. True "set to
+ *               absolute" semantics require ObservableGauge with a callback;
+ *               deferred to a v2 interface.
+ *
+ * Instrument instances are lazily created and cached per name so repeated
+ * calls to the same metric name reuse the same OTel instrument.
+ */
+export class OtelMetrics implements IMetrics {
+  private readonly meter = metrics.getMeter("@repo/core-shared", "1.0.0");
+  private readonly counters = new Map<string, Counter>();
+  private readonly histograms = new Map<string, Histogram>();
+  private readonly gauges = new Map<string, UpDownCounter>();
+
+  counter(
+    name: string,
+    value = 1,
+    attributes?: Record<string, MetricAttributeValue>,
+  ): void {
+    let counter = this.counters.get(name);
+    if (!counter) {
+      counter = this.meter.createCounter(name);
+      this.counters.set(name, counter);
+    }
+    counter.add(value, attributes);
+  }
+
+  histogram(
+    name: string,
+    value: number,
+    attributes?: Record<string, MetricAttributeValue>,
+  ): void {
+    let histogram = this.histograms.get(name);
+    if (!histogram) {
+      histogram = this.meter.createHistogram(name);
+      this.histograms.set(name, histogram);
+    }
+    histogram.record(value, attributes);
+  }
+
+  /**
+   * Records a gauge value via UpDownCounter.
+   *
+   * Note: UpDownCounter accumulates a running delta — each call adds to the
+   * previous value rather than replacing it. This is a synchronous approximation
+   * of gauge semantics. For true "set to absolute value" behaviour, use an
+   * ObservableGauge with a periodic callback instead (a future v2 addition).
+   */
+  gauge(
+    name: string,
+    value: number,
+    attributes?: Record<string, MetricAttributeValue>,
+  ): void {
+    let gauge = this.gauges.get(name);
+    if (!gauge) {
+      gauge = this.meter.createUpDownCounter(name);
+      this.gauges.set(name, gauge);
+    }
+    gauge.add(value, attributes);
+  }
+}