diff --git a/packages/orchestrator/pkg/sandbox/sandbox.go b/packages/orchestrator/pkg/sandbox/sandbox.go
index b24ce64c06..0e5fd19e4e 100644
--- a/packages/orchestrator/pkg/sandbox/sandbox.go
+++ b/packages/orchestrator/pkg/sandbox/sandbox.go
@@ -48,6 +48,17 @@ var (
 	meter                        = otel.Meter("github.com/e2b-dev/infra/packages/orchestrator/pkg/sandbox")
 	envdInitCalls                = utils.Must(telemetry.GetCounter(meter, telemetry.EnvdInitCalls))
 	waitForEnvdDurationHistogram = utils.Must(telemetry.GetHistogram(meter, telemetry.WaitForEnvdDurationHistogramName))
+
+	uffdStartupPagesHistogram       = utils.Must(telemetry.GetHistogram(meter, telemetry.UffdStartupPagesHistogramName))
+	uffdStartupSourcePagesHistogram = utils.Must(telemetry.GetHistogram(meter, telemetry.UffdStartupSourcePagesHistogramName))
+	uffdStartupBytesHistogram       = utils.Must(telemetry.GetHistogram(meter, telemetry.UffdStartupBytesHistogramName))
+)
+
+// Sandbox start types recorded on the orchestrator.sandbox.uffd.startup.*
+// metrics via the start_type attribute.
+const (
+	StartTypeCreate = "create" // cold boot (template build)
+	StartTypeResume = "resume" // resume from a snapshot (the common runtime path)
 )
 
 var SandboxHttpTransport = otelhttp.NewTransport(
@@ -256,6 +267,14 @@ type Sandbox struct {
 	exit *utils.ErrorOnce
 
 	stop utils.Lazy[error]
+
+	// startupStatsOnce guards the orchestrator.sandbox.uffd.startup.* recording
+	// so it fires only on the first WaitForEnvd — the actual sandbox start.
+	// ServeStats() is lifetime-cumulative on the UFFD handler, so a later
+	// WaitForEnvd on the same handler (e.g. the envd-binary swap + restart in a
+	// template build) would otherwise emit a sample inflated with post-startup
+	// faults rather than that init's working set.
+	startupStatsOnce sync.Once
 }
 
 func (s *Sandbox) LoggerMetadata() sbxlogger.SandboxMetadata {
@@ -911,6 +930,7 @@ func (f *Factory) ResumeSandbox(
 
 	err = sbx.WaitForEnvd(
 		ctx,
+		StartTypeResume,
 		f.config.EnvdTimeout,
 	)
 	if err != nil {
@@ -1457,6 +1477,7 @@ func (s *Sandbox) WaitForExit(ctx context.Context) error {
 
 func (s *Sandbox) WaitForEnvd(
 	ctx context.Context,
+	startType string,
 	timeout time.Duration,
 ) (e error) {
 	start := time.Now()
@@ -1471,6 +1492,25 @@ func (s *Sandbox) WaitForEnvd(
 			attribute.Bool("success", e == nil),
 		))
 
+		// Record the demand-fault working set the guest needed to reach this
+		// point. Only on the first WaitForEnvd: it is the actual start, and
+		// ServeStats() is cumulative since resume, so at this instant it equals
+		// the startup counts. A later WaitForEnvd on the same handler (e.g. the
+		// envd-binary swap + restart during a template build) would otherwise
+		// re-report a cumulative total polluted with intervening faults.
+		// Recorded for both outcomes (success label) so slow/failed starts can
+		// be correlated with page volume.
+		s.startupStatsOnce.Do(func() {
+			stats := s.memory.ServeStats()
+			startupAttrs := metric.WithAttributes(
+				attribute.String("start_type", startType),
+				attribute.Bool("success", e == nil),
+			)
+			uffdStartupPagesHistogram.Record(ctx, stats.Pages, startupAttrs)
+			uffdStartupSourcePagesHistogram.Record(ctx, stats.SourcePages, startupAttrs)
+			uffdStartupBytesHistogram.Record(ctx, stats.Bytes, startupAttrs)
+		})
+
 		if e != nil {
 			return
 		}
diff --git a/packages/orchestrator/pkg/sandbox/uffd/memory_backend.go b/packages/orchestrator/pkg/sandbox/uffd/memory_backend.go
index 0d29bdb1c1..c79f5b3c56 100644
--- a/packages/orchestrator/pkg/sandbox/uffd/memory_backend.go
+++ b/packages/orchestrator/pkg/sandbox/uffd/memory_backend.go
@@ -7,6 +7,7 @@ import (
 
 	"github.com/e2b-dev/infra/packages/orchestrator/pkg/sandbox/block"
 	"github.com/e2b-dev/infra/packages/orchestrator/pkg/sandbox/fc"
+	"github.com/e2b-dev/infra/packages/orchestrator/pkg/sandbox/uffd/userfaultfd"
 	"github.com/e2b-dev/infra/packages/shared/pkg/storage/header"
 	"github.com/e2b-dev/infra/packages/shared/pkg/utils"
 )
@@ -22,4 +23,8 @@ type MemoryBackend interface {
 	Ready() chan struct{}
 	Exit() *utils.ErrorOnce
 	Memfd(ctx context.Context) *block.Memfd
+	// ServeStats returns a cumulative snapshot of demand faults served so far.
+	// Sampled at the envd-init boundary it yields the pages/bytes a guest
+	// needed to start.
+	ServeStats() userfaultfd.ServeSnapshot
 }
diff --git a/packages/orchestrator/pkg/sandbox/uffd/noop.go b/packages/orchestrator/pkg/sandbox/uffd/noop.go
index f95722e389..c4f4a9bbba 100644
--- a/packages/orchestrator/pkg/sandbox/uffd/noop.go
+++ b/packages/orchestrator/pkg/sandbox/uffd/noop.go
@@ -9,6 +9,7 @@ import (
 
 	"github.com/e2b-dev/infra/packages/orchestrator/pkg/sandbox/block"
 	"github.com/e2b-dev/infra/packages/orchestrator/pkg/sandbox/fc"
+	"github.com/e2b-dev/infra/packages/orchestrator/pkg/sandbox/uffd/userfaultfd"
 	"github.com/e2b-dev/infra/packages/shared/pkg/storage/header"
 	"github.com/e2b-dev/infra/packages/shared/pkg/utils"
 )
@@ -87,3 +88,9 @@ func (m *NoopMemory) Exit() *utils.ErrorOnce {
 func (m *NoopMemory) Memfd(context.Context) *block.Memfd {
 	return nil
 }
+
+// ServeStats returns a zero snapshot: NoopMemory has no UFFD serve loop, so no
+// pages are demand-faulted through it.
+func (m *NoopMemory) ServeStats() userfaultfd.ServeSnapshot {
+	return userfaultfd.ServeSnapshot{}
+}
diff --git a/packages/orchestrator/pkg/sandbox/uffd/uffd.go b/packages/orchestrator/pkg/sandbox/uffd/uffd.go
index e8d8413f1f..d5bd429116 100644
--- a/packages/orchestrator/pkg/sandbox/uffd/uffd.go
+++ b/packages/orchestrator/pkg/sandbox/uffd/uffd.go
@@ -281,3 +281,15 @@ func (u *Uffd) PrefetchData(ctx context.Context) (block.PrefetchData, error) {
 func (u *Uffd) Memfd(_ context.Context) *block.Memfd {
 	return u.memfd.Swap(nil)
 }
+
+// ServeStats returns a cumulative snapshot of demand faults served so far, or a
+// zero snapshot if the handler has not been created yet (FC has not connected).
+// It never blocks.
+func (u *Uffd) ServeStats() userfaultfd.ServeSnapshot {
+	handler, err := u.handler.Result()
+	if err != nil {
+		return userfaultfd.ServeSnapshot{}
+	}
+
+	return handler.ServeStats()
+}
diff --git a/packages/orchestrator/pkg/sandbox/uffd/userfaultfd/metrics.go b/packages/orchestrator/pkg/sandbox/uffd/userfaultfd/metrics.go
index cc04495fcd..56a2945419 100644
--- a/packages/orchestrator/pkg/sandbox/uffd/userfaultfd/metrics.go
+++ b/packages/orchestrator/pkg/sandbox/uffd/userfaultfd/metrics.go
@@ -118,6 +118,51 @@ var prefaultTimer = utils.Must(telemetry.NewTimerFactory(
 	"UFFD prefault attempts",
 ))
 
+// ServeSnapshot is a cumulative count of demand faults a handler has served,
+// read at a point in time via Userfaultfd.ServeStats. Prefaults bypass the
+// serve loop and are not counted. Sampling it at the envd-init boundary yields
+// the pages/bytes a guest needed to start.
+type ServeSnapshot struct {
+	// Pages is the number of demand faults resolved (installed or already
+	// present) — the count of distinct pages the guest needed.
+	Pages int64
+	// SourcePages is the subset of Pages installed from the source
+	// (page_class=new); the rest were zero-filled or already resident (a
+	// prefetch hit or a concurrent install).
+	SourcePages int64
+	// Bytes is the number of bytes installed into the guest by this handler
+	// (page_class new + zero). On a fixed page size this is Pages-minus-present
+	// times the page size, but it is tracked directly so it stays correct
+	// across mixed page sizes.
+	Bytes int64
+}
+
+// ServeStats returns a cumulative snapshot of the demand faults served so far.
+func (u *Userfaultfd) ServeStats() ServeSnapshot {
+	return ServeSnapshot{
+		Pages:       u.servedPages.Load(),
+		SourcePages: u.servedSourcePages.Load(),
+		Bytes:       u.servedBytes.Load(),
+	}
+}
+
+// recordServeStats folds one finished serve attempt into the cumulative
+// counters read by ServeStats. Only resolved faults (installed or already
+// present) count as a needed page; deferred faults are re-served and counted
+// when they finally resolve, so they are not double counted here.
+func (u *Userfaultfd) recordServeStats(pclass pageClass, result faultResult, servedBytes int64) {
+	switch result {
+	case faultResultInstalled, faultResultPresent:
+		u.servedPages.Add(1)
+		if servedBytes > 0 {
+			u.servedBytes.Add(servedBytes)
+			if pclass == pageClassNew {
+				u.servedSourcePages.Add(1)
+			}
+		}
+	}
+}
+
 // prefaultAttrs holds a precomputed metric.MeasurementOption per faultResult.
 // Prefaults have no page_class: they only ever target not-present pages (the
 // Dirty/Zero pre-check records result="skipped" instead).
diff --git a/packages/orchestrator/pkg/sandbox/uffd/userfaultfd/metrics_test.go b/packages/orchestrator/pkg/sandbox/uffd/userfaultfd/metrics_test.go
index 8b60eefa56..5262b1b654 100644
--- a/packages/orchestrator/pkg/sandbox/uffd/userfaultfd/metrics_test.go
+++ b/packages/orchestrator/pkg/sandbox/uffd/userfaultfd/metrics_test.go
@@ -144,6 +144,36 @@ func TestPrefaultMetric(t *testing.T) {
 	assert.Equal(t, int64(0), bytesSum["deferred"])
 }
 
+// TestServeStats folds the same mix of finished serve attempts that
+// TestServeMetric records and asserts the cumulative ServeStats() snapshot —
+// the point-in-time count the startup metric samples at the envd-init boundary.
+// Only resolved faults (installed or already-present) count as a needed page;
+// deferred and errored attempts do not, so a deferred fault is not
+// double-counted when it is later re-served and resolves.
+func TestServeStats(t *testing.T) {
+	t.Parallel()
+
+	pageSize := int64(header.PageSize)
+
+	var u Userfaultfd
+	fold := func(class pageClass, result faultResult, bytes int64, n int) {
+		for range n {
+			u.recordServeStats(class, result, bytes)
+		}
+	}
+	fold(pageClassNew, faultResultInstalled, pageSize, 3)  // +3 pages, +3 source, +3 pages of bytes
+	fold(pageClassZero, faultResultInstalled, pageSize, 1) // +1 page, +1 page of bytes (not source)
+	fold(pageClassResident, faultResultPresent, 0, 2)      // +2 pages, no bytes
+	fold(pageClassNew, faultResultPresent, 0, 1)           // +1 page (lost race), no bytes/source
+	fold(pageClassNew, faultResultDeferred, 0, 1)          // not counted (re-served later)
+	fold(pageClassNew, faultResultError, 0, 1)             // not counted (never resolved)
+
+	stats := u.ServeStats()
+	assert.Equal(t, int64(7), stats.Pages, "resolved demand faults (installed+present)")
+	assert.Equal(t, int64(3), stats.SourcePages, "subset installed from the source")
+	assert.Equal(t, 4*pageSize, stats.Bytes, "bytes installed (new+zero), present/deferred/error contribute none")
+}
+
 func key(pageClass, result string) string { return pageClass + "/" + result }
 
 // attrKey returns "page_class/result" for serve datapoints and just "result"
diff --git a/packages/orchestrator/pkg/sandbox/uffd/userfaultfd/userfaultfd.go b/packages/orchestrator/pkg/sandbox/uffd/userfaultfd/userfaultfd.go
index 2359d79162..1e20fa50ae 100644
--- a/packages/orchestrator/pkg/sandbox/uffd/userfaultfd/userfaultfd.go
+++ b/packages/orchestrator/pkg/sandbox/uffd/userfaultfd/userfaultfd.go
@@ -108,6 +108,15 @@ type Userfaultfd struct {
 	// that has already been closed (and potentially recycled by the OS).
 	closed bool
 
+	// Cumulative demand-fault serve counters, read via ServeStats(). They
+	// mirror the orchestrator.sandbox.uffd.serve metric but as a per-handler
+	// snapshot, so a caller can sample "how many pages did this guest need so
+	// far" at a point in time (e.g. the moment envd init returns). Prefaults
+	// bypass the serve loop and are not counted here. See recordServeStats.
+	servedPages       atomic.Int64 // faults resolved (installed or already-present)
+	servedSourcePages atomic.Int64 // subset installed from the source (page_class=new)
+	servedBytes       atomic.Int64 // bytes installed into the guest (new + zero)
+
 	logger logger.Logger
 }
 
@@ -417,7 +426,10 @@ func (u *Userfaultfd) Serve(
 				pclass := pageClassUnknown
 				result := faultResultInstalled
 				var servedBytes int64
-				defer func() { sw.RecordRaw(ctx, servedBytes, serveAttrs[pclass][result]) }()
+				defer func() {
+					sw.RecordRaw(ctx, servedBytes, serveAttrs[pclass][result])
+					u.recordServeStats(pclass, result, servedBytes)
+				}()
 
 				if h := u.testFaultHook.Load(); h != nil {
 					(*h)(addr, faultPhaseBeforeRLock)
diff --git a/packages/orchestrator/pkg/template/build/layer/create_sandbox.go b/packages/orchestrator/pkg/template/build/layer/create_sandbox.go
index e14705e41e..0c0f012240 100644
--- a/packages/orchestrator/pkg/template/build/layer/create_sandbox.go
+++ b/packages/orchestrator/pkg/template/build/layer/create_sandbox.go
@@ -167,6 +167,7 @@ func (cs *CreateSandbox) Sandbox(
 
 	err = sbx.WaitForEnvd(
 		ctx,
+		sandbox.StartTypeCreate,
 		waitEnvdTimeout,
 	)
 	if err != nil {
diff --git a/packages/orchestrator/pkg/template/build/layer/layer_executor.go b/packages/orchestrator/pkg/template/build/layer/layer_executor.go
index 642cd09aa2..ad1f0ad23a 100644
--- a/packages/orchestrator/pkg/template/build/layer/layer_executor.go
+++ b/packages/orchestrator/pkg/template/build/layer/layer_executor.go
@@ -235,6 +235,7 @@ func (lb *LayerExecutor) updateEnvdInSandbox(
 	// Step 4: Wait for envd to initialize
 	err = sbx.WaitForEnvd(
 		ctx,
+		sandbox.StartTypeCreate,
 		waitEnvdTimeout,
 	)
 	if err != nil {
diff --git a/packages/shared/pkg/telemetry/meters.go b/packages/shared/pkg/telemetry/meters.go
index bf55b2094b..a09d5c0ada 100644
--- a/packages/shared/pkg/telemetry/meters.go
+++ b/packages/shared/pkg/telemetry/meters.go
@@ -75,6 +75,14 @@ const (
 	OrchestratorSandboxCreateDurationName HistogramType = "orchestrator.sandbox.create.duration"
 	WaitForEnvdDurationHistogramName      HistogramType = "orchestrator.sandbox.envd.init.duration"
 
+	// Sandbox startup working-set histograms: demand-fault pages/bytes a guest
+	// needed to reach a successful envd init, recorded once per start. Sampled
+	// per start (not per fault), so histogram_quantile yields per-sandbox
+	// percentiles.
+	UffdStartupPagesHistogramName       HistogramType = "orchestrator.sandbox.uffd.startup.pages"
+	UffdStartupSourcePagesHistogramName HistogramType = "orchestrator.sandbox.uffd.startup.source_pages"
+	UffdStartupBytesHistogramName       HistogramType = "orchestrator.sandbox.uffd.startup.bytes"
+
 	// TCP Firewall histograms
 	TCPFirewallConnectionDurationHistogramName    HistogramType = "orchestrator.tcpfirewall.connection.duration"
 	TCPFirewallConnectionsPerSandboxHistogramName HistogramType = "orchestrator.tcpfirewall.connections.per_sandbox"
@@ -382,6 +390,10 @@ var histogramDesc = map[HistogramType]string{
 	OrchestratorSandboxCreateDurationName: "Time taken to create a sandbox",
 	WaitForEnvdDurationHistogramName:      "Time taken for Envd to initialize successfully",
 
+	UffdStartupPagesHistogramName:       "Demand-fault pages a guest needed to reach a successful envd init, per start",
+	UffdStartupSourcePagesHistogramName: "Subset of startup demand-fault pages pulled from the source (e.g. GCS), per start",
+	UffdStartupBytesHistogramName:       "Bytes faulted into a guest to reach a successful envd init, per start",
+
 	TCPFirewallConnectionDurationHistogramName:    "Duration of TCP firewall proxied connections",
 	TCPFirewallConnectionsPerSandboxHistogramName: "Number of active TCP firewall connections per sandbox",
 
@@ -422,6 +434,9 @@ var histogramUnits = map[HistogramType]string{
 	BuildRootfsSizeHistogramName:                  "{By}",
 	OrchestratorSandboxCreateDurationName:         "ms",
 	WaitForEnvdDurationHistogramName:              "ms",
+	UffdStartupPagesHistogramName:                 "{page}",
+	UffdStartupSourcePagesHistogramName:           "{page}",
+	UffdStartupBytesHistogramName:                 "{By}",
 	TCPFirewallConnectionDurationHistogramName:    "ms",
 	TCPFirewallConnectionsPerSandboxHistogramName: "{connection}",