diff --git a/util/util.go b/util/util.go
index 170b4ae99..75c93d4f2 100644
--- a/util/util.go
+++ b/util/util.go
@@ -23,6 +23,7 @@ import (
 	"os"
 	"unicode/utf8"
 
+	"github.com/google/uuid"
 	"github.com/h2non/filetype"
 
 	"github.com/cloudbase/garm-provider-common/cloudconfig"
@@ -32,6 +33,20 @@ import (
 	"github.com/cloudbase/garm/runner/common"
 )
 
+// scaleSetPoolIDNamespace is the UUIDv5 namespace used to derive pseudo pool
+// IDs for scale sets. Instances in providers are tagged with IDs derived from
+// this namespace; changing it (or the derivation input format) orphans every
+// instance created with the previous value.
+var scaleSetPoolIDNamespace = uuid.MustParse("3f5bfba0-d82c-4f91-a5f6-ddc1c9209b01")
+
+// ScaleSetPseudoPoolID derives a stable, UUID-shaped pseudo pool ID for a
+// scale set, from the forge entity ID and the internal scale set database ID.
+// Both inputs are immutable, so the result never changes for the lifetime of
+// the scale set and always fits within provider tag/label length limits.
+func ScaleSetPseudoPoolID(entityID string, scaleSetID uint) string {
+	return uuid.NewSHA1(scaleSetPoolIDNamespace, fmt.Appendf(nil, "%s-%d", entityID, scaleSetID)).String()
+}
+
 func FetchTools(ctx context.Context, cli common.GithubClient) ([]commonParams.RunnerApplicationDownload, error) {
 	tools, ghResp, err := cli.ListEntityRunnerApplicationDownloads(ctx)
 	if err != nil {
diff --git a/workers/provider/instance_manager.go b/workers/provider/instance_manager.go
index f276bd404..2ba88d4d5 100644
--- a/workers/provider/instance_manager.go
+++ b/workers/provider/instance_manager.go
@@ -148,8 +148,9 @@ func (i *instanceManager) getEntity() (params.ForgeEntity, error) {
 }
 
 func (i *instanceManager) pseudoPoolID() string {
-	// This is temporary. We need to extend providers to know about scale sets.
-	return fmt.Sprintf("%s-%s", i.scaleSet.Name, i.scaleSetEntity.ID)
+	// nolint:golangci-lint,godox
+	// TODO(gabriel-samfira): extend providers to know about scale sets.
+	return garmUtil.ScaleSetPseudoPoolID(i.scaleSetEntity.ID, i.scaleSet.ID)
 }
 
 func (i *instanceManager) handleCreateInstanceInProvider(instance params.Instance) error {
diff --git a/workers/scaleset/scaleset.go b/workers/scaleset/scaleset.go
index 418756c0d..d6db786fc 100644
--- a/workers/scaleset/scaleset.go
+++ b/workers/scaleset/scaleset.go
@@ -62,6 +62,7 @@ func NewWorker(ctx context.Context, store dbCommon.Store, scaleSet params.ScaleS
 		scaleSet:       scaleSet,
 		entity:         entity,
 		runners:        make(map[string]params.Instance),
+		pseudoPoolID:   garmUtil.ScaleSetPseudoPoolID(scalesetEntity.ID, scaleSet.ID),
 	}, nil
 }
 
@@ -76,6 +77,14 @@ type Worker struct {
 	entity   params.ForgeEntity
 	runners  map[string]params.Instance
 
+	// pseudoPoolID is the stable pool ID reported to providers for this scale
+	// set. It is derived from immutable IDs, so it is computed once.
+	pseudoPoolID string
+	// legacyPoolIDDrained indicates that the provider no longer has any
+	// instances tagged with the legacy name-based pseudo pool ID, so we can
+	// stop querying for it.
+	legacyPoolIDDrained bool
+
 	consumer dbCommon.Consumer
 
 	listener *scaleSetListener
@@ -551,10 +560,6 @@ func (w *Worker) consolidateRunnerState(runners []params.RunnerReference) error
 // DB runners with no provider instance are marked as pending_delete. Must be
 // called with w.mux held.
 func (w *Worker) consolidateProviderState() error {
-	pseudoPoolID, err := w.pseudoPoolID()
-	if err != nil {
-		return fmt.Errorf("getting pseudo pool ID: %w", err)
-	}
 	listParams := common.ListInstancesParams{
 		ListInstancesV011: common.ListInstancesV011Params{
 			ProviderBaseParams: common.ProviderBaseParams{
@@ -563,7 +568,7 @@ func (w *Worker) consolidateProviderState() error {
 		},
 	}
 
-	providerRunners, err := w.provider.ListInstances(w.ctx, pseudoPoolID, listParams)
+	providerRunners, err := w.provider.ListInstances(w.ctx, w.pseudoPoolID, listParams)
 	if err != nil {
 		return fmt.Errorf("listing instances: %w", err)
 	}
@@ -573,6 +578,27 @@ func (w *Worker) consolidateProviderState() error {
 		providerRunnersByName[runner.Name] = runner
 	}
 
+	if !w.legacyPoolIDDrained {
+		legacyID, err := w.legacyPseudoPoolID()
+		if err != nil {
+			return fmt.Errorf("getting legacy pseudo pool ID: %w", err)
+		}
+		legacyRunners, err := w.provider.ListInstances(w.ctx, legacyID, listParams)
+		if err != nil {
+			return fmt.Errorf("listing instances by legacy pseudo pool ID: %w", err)
+		}
+		if len(legacyRunners) == 0 {
+			w.legacyPoolIDDrained = true
+		}
+		for _, runner := range legacyRunners {
+			if _, ok := providerRunnersByName[runner.Name]; ok {
+				continue
+			}
+			providerRunnersByName[runner.Name] = runner
+			providerRunners = append(providerRunners, runner)
+		}
+	}
+
 	deleteInstanceParams := common.DeleteInstanceParams{
 		DeleteInstanceV011: common.DeleteInstanceV011Params{
 			ProviderBaseParams: common.ProviderBaseParams{
@@ -637,8 +663,16 @@ func (w *Worker) consolidateProviderState() error {
 	return nil
 }
 
-func (w *Worker) pseudoPoolID() (string, error) {
-	// This is temporary. We need to extend providers to know about scale sets.
+// legacyPseudoPoolID returns the deprecated name-based pseudo pool ID. Older
+// GARM versions tagged provider instances with this ID, so we keep listing by
+// it until no instances tagged with it remain. It must be recomputed on every
+// call, because the scale set name can change (which is bad and have failed to
+// consider this until now).
+//
+// Deprecated: This function is "born" deprecated because it transitions from
+// the old way to tag instances, to the new stable uuid V5 computed from the
+// entity ID and the internal scaleset ID.
+func (w *Worker) legacyPseudoPoolID() (string, error) {
 	entity, err := w.scaleSet.GetEntity()
 	if err != nil {
 		return "", fmt.Errorf("getting entity: %w", err)