diff --git a/contracts/eks/v1/v1_compat_test.go b/contracts/eks/v1/v1_compat_test.go
new file mode 100644
index 000000000..a87532d21
--- /dev/null
+++ b/contracts/eks/v1/v1_compat_test.go
@@ -0,0 +1,34 @@
+package eksv1
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// A v1 decoder ignores fields a later sender adds, so a report carrying them
+// decodes to the same value as one without.
+func TestAddonStatusReport_IgnoresUnknownFields(t *testing.T) {
+	body := `{"addon":"argocd","version":"3.0.23","phase":"ready","message":"","ts":1736935200,` +
+		`"incarnationId":"inc-1","generation":4,"executorEpoch":7}`
+	var got AddonStatusReport
+	require.NoError(t, json.Unmarshal([]byte(body), &got))
+	require.Equal(t, AddonStatusReport{Addon: "argocd", Version: "3.0.23", Phase: AddonPhaseReady, TS: 1736935200}, got)
+}
+
+// Both deployed body forms tolerate added top-level and per-add-on fields.
+func TestInternalAddonsResponse_IgnoresUnknownFields(t *testing.T) {
+	for name, body := range map[string]string{
+		"rest-json": `{"Addons":[{"AddonName":"spinifex-noop","AddonVersion":"0.1.0","ServiceAccountRoleArn":"",` +
+			`"ConfigurationValues":"","IncarnationId":"inc-1","Generation":4}],"ExecutorEpoch":7}`,
+		"encoding-json": `{"addons":[{"addonName":"spinifex-noop","addonVersion":"0.1.0",` +
+			`"incarnationId":"inc-1","generation":4}],"executorEpoch":7}`,
+	} {
+		t.Run(name, func(t *testing.T) {
+			var got InternalAddonsResponse
+			require.NoError(t, json.Unmarshal([]byte(body), &got))
+			require.Equal(t, InternalAddonsResponse{Addons: []StagedAddonManifest{{AddonName: "spinifex-noop", AddonVersion: "0.1.0"}}}, got)
+		})
+	}
+}
diff --git a/spinifex/agents/eks/gatewayfetch/v1_compat_test.go b/spinifex/agents/eks/gatewayfetch/v1_compat_test.go
new file mode 100644
index 000000000..a5524c803
--- /dev/null
+++ b/spinifex/agents/eks/gatewayfetch/v1_compat_test.go
@@ -0,0 +1,23 @@
+package gatewayfetch
+
+import (
+	"bytes"
+	"testing"
+)
+
+// Fields a later gateway adds never reach the four TSV columns the on-VM
+// addon-sync agent reads.
+func TestEmitAddonsTSV_IgnoresUnknownFields(t *testing.T) {
+	body := []byte(`{"Addons":[{"AddonName":"aws-load-balancer-controller","AddonVersion":"2.11.0",` +
+		`"ServiceAccountRoleArn":"arn:aws:iam::123456789012:role/alb","ConfigurationValues":"a\tb",` +
+		`"IncarnationId":"inc-1","Generation":4}],"ExecutorEpoch":7}`)
+
+	var buf bytes.Buffer
+	if err := emitAddonsTSV(&buf, body); err != nil {
+		t.Fatalf("emitAddonsTSV: %v", err)
+	}
+	want := "aws-load-balancer-controller\t2.11.0\tarn:aws:iam::123456789012:role/alb\tYQli\n"
+	if buf.String() != want {
+		t.Fatalf("TSV mismatch:\n got: %q\nwant: %q", buf.String(), want)
+	}
+}
diff --git a/spinifex/domains/eks/addon/v1_compat_test.go b/spinifex/domains/eks/addon/v1_compat_test.go
new file mode 100644
index 000000000..2f03105da
--- /dev/null
+++ b/spinifex/domains/eks/addon/v1_compat_test.go
@@ -0,0 +1,159 @@
+package addon
+
+import (
+	"context"
+	"encoding/json"
+	"slices"
+	"testing"
+
+	"github.com/nats-io/nats.go/jetstream"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// newerRecordJSON is a record as a later binary might store it: every v1 field
+// plus fields this binary's Record does not declare.
+const newerRecordJSON = `{"addonName":"argocd","addonVersion":"3.0.23","status":"ACTIVE",` +
+	`"arn":"arn:aws:eks:us-east-1:111122223333:addon/c1/argocd",` +
+	`"createdAt":"2026-06-08T00:00:00Z","modifiedAt":"2026-06-08T00:00:00Z",` +
+	`"incarnationId":"inc-1","generation":4,"observedGeneration":3,"origin":"user"}`
+
+const newerManifestJSON = `{"addonName":"argocd","addonVersion":"3.0.23",` +
+	`"incarnationId":"inc-1","generation":4}`
+
+func seedNewerRecord(t *testing.T, kv jetstream.KeyValue) {
+	t.Helper()
+	_, err := kv.Put(t.Context(), "clusters/c1/addons/argocd", []byte(newerRecordJSON))
+	require.NoError(t, err)
+	_, err = kv.Put(t.Context(), "clusters/c1/addons/argocd/manifest", []byte(newerManifestJSON))
+	require.NoError(t, err)
+}
+
+func storedKeys(t *testing.T, kv jetstream.KeyValue, key string) []string {
+	t.Helper()
+	entry, err := kv.Get(t.Context(), key)
+	require.NoError(t, err)
+	var top map[string]json.RawMessage
+	require.NoError(t, json.Unmarshal(entry.Value(), &top))
+	keys := make([]string, 0, len(top))
+	for k := range top {
+		keys = append(keys, k)
+	}
+	slices.Sort(keys)
+	return keys
+}
+
+// Every owner write is decode-into-Record then re-encode, so fields this
+// binary does not declare are erased from the record and the re-staged manifest.
+func TestOwnerWrites_DropUnknownRecordAndManifestFields(t *testing.T) {
+	t.Parallel()
+	failed := "image pull"
+	for _, tc := range []struct {
+		name         string
+		write        func(t *testing.T, o *Owner, kv jetstream.KeyValue)
+		wantRecord   []string
+		wantManifest []string
+	}{
+		{
+			name: "Update",
+			write: func(t *testing.T, o *Owner, kv jetstream.KeyValue) {
+				_, err := o.Update(t.Context(), kv, testAccountID, "c1", "argocd", Change{})
+				require.NoError(t, err)
+			},
+			wantRecord:   []string{"addonName", "addonVersion", "arn", "createdAt", "modifiedAt", "status"},
+			wantManifest: []string{"addonName", "addonVersion"},
+		},
+		{
+			name: "ApplyReport failed",
+			write: func(t *testing.T, o *Owner, kv jetstream.KeyValue) {
+				require.NoError(t, o.ApplyReport(t.Context(), kv, "c1", Report{Addon: "argocd", Phase: PhaseFailed, Message: failed}))
+			},
+			wantRecord:   []string{"addonName", "addonVersion", "arn", "createdAt", "health", "modifiedAt", "status"},
+			wantManifest: []string{"addonName", "addonVersion", "generation", "incarnationId"},
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			kv := newTestKV(t)
+			seedNewerRecord(t, kv)
+			o := New("us-east-1", NewStagingInstaller(func(_ context.Context, _ string) (jetstream.KeyValue, error) { return kv, nil }))
+			tc.write(t, o, kv)
+			assert.Equal(t, tc.wantRecord, storedKeys(t, kv, "clusters/c1/addons/argocd"))
+			assert.Equal(t, tc.wantManifest, storedKeys(t, kv, "clusters/c1/addons/argocd/manifest"))
+		})
+	}
+}
+
+// ApplyReport skips the write when nothing changes, so a no-op report leaves
+// unknown fields in place.
+func TestOwnerApplyReport_NoOpKeepsUnknownFields(t *testing.T) {
+	t.Parallel()
+	kv := newTestKV(t)
+	seedNewerRecord(t, kv)
+	o := New("us-east-1", &fakeInstaller{})
+
+	require.NoError(t, o.ApplyReport(t.Context(), kv, "c1", Report{Addon: "argocd", Phase: PhaseReady}))
+
+	entry, err := kv.Get(t.Context(), "clusters/c1/addons/argocd")
+	require.NoError(t, err)
+	assert.JSONEq(t, newerRecordJSON, string(entry.Value()))
+}
+
+func TestOwnerDelete_ErasesRecordAndManifestWithUnknownFields(t *testing.T) {
+	t.Parallel()
+	kv := newTestKV(t)
+	seedNewerRecord(t, kv)
+	inst := &fakeInstaller{}
+	o := New("us-east-1", inst)
+
+	rec, err := o.Delete(t.Context(), kv, testAccountID, "c1", "argocd")
+	require.NoError(t, err)
+	assert.Equal(t, StatusDeleting, rec.Status)
+	assert.Equal(t, []string{"argocd"}, inst.uninstalls)
+
+	_, err = kv.Get(t.Context(), "clusters/c1/addons/argocd")
+	require.ErrorIs(t, err, jetstream.ErrKeyNotFound)
+	_, err = kv.Get(t.Context(), "clusters/c1/addons/argocd/manifest")
+	require.ErrorIs(t, err, jetstream.ErrKeyNotFound)
+}
+
+// Reads ignore unknown fields and never write back.
+func TestReads_IgnoreUnknownFieldsWithoutRewriting(t *testing.T) {
+	t.Parallel()
+	kv := newTestKV(t)
+	seedNewerRecord(t, kv)
+
+	rec, err := Get(t.Context(), kv, "c1", "argocd")
+	require.NoError(t, err)
+	assert.Equal(t, StatusActive, rec.Status)
+
+	recs, err := List(t.Context(), kv, "c1")
+	require.NoError(t, err)
+	require.Len(t, recs, 1)
+	assert.Equal(t, "3.0.23", recs[0].AddonVersion)
+
+	ms, err := ListManifests(t.Context(), kv, "c1")
+	require.NoError(t, err)
+	assert.Equal(t, []Manifest{{AddonName: "argocd", AddonVersion: "3.0.23"}}, ms)
+
+	entry, err := kv.Get(t.Context(), "clusters/c1/addons/argocd")
+	require.NoError(t, err)
+	assert.Equal(t, uint64(1), entry.Revision())
+}
+
+// A field whose JSON type changes is not ignored: one undecodable record fails
+// the whole cluster listing, and one undecodable manifest fails guest delivery.
+func TestList_OneUndecodableEntryFailsTheListing(t *testing.T) {
+	t.Parallel()
+	kv := newTestKV(t)
+	require.NoError(t, put(t.Context(), kv, "c1", sampleRecord("argocd")))
+	_, err := kv.Put(t.Context(), "clusters/c1/addons/coredns", []byte(`{"addonName":"coredns","status":1}`))
+	require.NoError(t, err)
+	_, err = kv.Put(t.Context(), "clusters/c1/addons/coredns/manifest", []byte(`{"addonName":"coredns","addonVersion":2}`))
+	require.NoError(t, err)
+
+	_, err = List(t.Context(), kv, "c1")
+	require.ErrorContains(t, err, "unmarshal addon clusters/c1/addons/coredns")
+	_, err = ListManifests(t.Context(), kv, "c1")
+	require.ErrorContains(t, err, "unmarshal staged manifest clusters/c1/addons/coredns/manifest")
+}
diff --git a/spinifex/handlers/eks/addon_v1_compat_test.go b/spinifex/handlers/eks/addon_v1_compat_test.go
new file mode 100644
index 000000000..5af6c363e
--- /dev/null
+++ b/spinifex/handlers/eks/addon_v1_compat_test.go
@@ -0,0 +1,48 @@
+package handlers_eks
+
+import (
+	"context"
+	"testing"
+
+	eksv1 "github.com/mulgadc/spinifex/contracts/eks/v1"
+	"github.com/mulgadc/spinifex/spinifex/domains/eks/addon"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// The reconciler's subscriber decodes then applies; a report carrying fields
+// this binary does not know is applied exactly as one without them.
+func TestAddonStatusReport_UnknownFieldsAreAppliedAsToday(t *testing.T) {
+	t.Parallel()
+	_, kv := setupStagingAddonService(t)
+	_, err := kv.Put(t.Context(), "clusters/c1/addons/argocd", []byte(`{"addonName":"argocd","addonVersion":"3.0.23",`+
+		`"status":"ACTIVE","arn":"arn","createdAt":"2026-06-08T00:00:00Z","modifiedAt":"2026-06-08T00:00:00Z"}`))
+	require.NoError(t, err)
+	r := &ClusterReconciler{acctKV: kv, clusterName: "c1", addonReports: addon.New("", nil)}
+
+	report, err := unmarshalAddonStatusReport([]byte(`{"addon":"argocd","version":"3.0.23","phase":"failed",` +
+		`"message":"rollout stalled","ts":1,"incarnationId":"stale-inc","generation":1}`))
+	require.NoError(t, err)
+	r.applyAddonStatusReport(t.Context(), report)
+
+	rec, err := addon.Get(t.Context(), kv, "c1", "argocd")
+	require.NoError(t, err)
+	assert.Equal(t, addon.StatusDegraded, rec.Status)
+	assert.Equal(t, "rollout stalled", rec.Health)
+}
+
+// The daemon copies the four v1 manifest fields onto the NATS reply, so a
+// staged manifest's unknown fields never reach the gateway or the guest.
+func TestListStagedAddonManifests_ProjectsOnlyV1Fields(t *testing.T) {
+	t.Parallel()
+	svc, kv := setupStagingAddonService(t)
+	_, err := kv.Put(t.Context(), albManifestKey, []byte(`{"addonName":"aws-load-balancer-controller",`+
+		`"addonVersion":"2.11.0","serviceAccountRoleArn":"`+addonLifecycleRoleARN+`","incarnationId":"inc-1","generation":4}`))
+	require.NoError(t, err)
+
+	out, err := svc.ListStagedAddonManifests(context.Background(), &ListStagedAddonManifestsInput{ClusterName: "c1"}, testAccountID)
+	require.NoError(t, err)
+	assert.Equal(t, []eksv1.StagedAddonManifest{{
+		AddonName: "aws-load-balancer-controller", AddonVersion: "2.11.0", ServiceAccountRoleArn: addonLifecycleRoleARN,
+	}}, out.Manifests)
+}