diff --git a/docs/ENVIRONMENT_VARIABLES.md b/docs/ENVIRONMENT_VARIABLES.md
index aa6c0b97f..57e2d11ac 100644
--- a/docs/ENVIRONMENT_VARIABLES.md
+++ b/docs/ENVIRONMENT_VARIABLES.md
@@ -177,4 +177,4 @@ Attribution is sent as `HTTP-Referer` and `X-Title`:
 - `AGENTFIELD_INFRON_APP_NAME` (default: `AgentField AI`)
 - `AGENTFIELD_INFRON_ATTRIBUTION=false`: Disable Infron attribution headers.
 
-When the `AGENTFIELD_INFRON_*` vars are unset, these OpenRouter attribution values are used as fallbacks, so a deployment that already declares its identity keeps it after switching gateways: `AGENTFIELD_OPENROUTER_SITE_URL`, `OR_SITE_URL`, `AGENTFIELD_OPENROUTER_APP_NAME`, `OR_APP_NAME`. If you do not want values configured for OpenRouter sent to Infron, set the `AGENTFIELD_INFRON_*` vars explicitly or disable attribution with `AGENTFIELD_INFRON_ATTRIBUTION=false`.
+When the `AGENTFIELD_INFRON_*` vars are unset, these OpenRouter attribution values are used as fallbacks, so a deployment that already declares its identity keeps it after switching gateways: `AGENTFIELD_OPENROUTER_SITE_URL`, `OR_SITE_URL`, `AGENTFIELD_OPENROUTER_APP_NAME`, `OR_APP_NAME`. The opt-out travels with them: when `AGENTFIELD_OPENROUTER_ATTRIBUTION=false`, these values are not inherited and the Infron defaults apply instead. To control Infron attribution specifically, set the `AGENTFIELD_INFRON_*` vars explicitly or disable it with `AGENTFIELD_INFRON_ATTRIBUTION=false`.
diff --git a/sdk/go/ai/infron_attribution.go b/sdk/go/ai/infron_attribution.go
index ae0240a97..6a4d48cf3 100644
--- a/sdk/go/ai/infron_attribution.go
+++ b/sdk/go/ai/infron_attribution.go
@@ -45,18 +45,33 @@ func resolveInfronAttribution(siteURL, siteName string) (string, string, bool) {
 		return "", "", false
 	}
 
+	// The OpenRouter-scoped values are honored as fallbacks so a deployment
+	// keeps its declared identity when it moves gateways — but the opt-out
+	// travels with them: values a deployment suppressed for one vendor (often
+	// because they name internal hosts or products) must not be sent to
+	// another.
+	inheritedURL, inheritedName := "", ""
+	if openRouterAttributionEnabled() {
+		inheritedURL = firstNonEmpty(
+			os.Getenv("AGENTFIELD_OPENROUTER_SITE_URL"),
+			os.Getenv("OR_SITE_URL"),
+		)
+		inheritedName = firstNonEmpty(
+			os.Getenv("AGENTFIELD_OPENROUTER_APP_NAME"),
+			os.Getenv("OR_APP_NAME"),
+		)
+	}
+
 	resolvedURL := firstNonEmpty(
 		siteURL,
 		os.Getenv("AGENTFIELD_INFRON_SITE_URL"),
-		os.Getenv("AGENTFIELD_OPENROUTER_SITE_URL"),
-		os.Getenv("OR_SITE_URL"),
+		inheritedURL,
 		defaultInfronSiteURL,
 	)
 	resolvedName := firstNonEmpty(
 		siteName,
 		os.Getenv("AGENTFIELD_INFRON_APP_NAME"),
-		os.Getenv("AGENTFIELD_OPENROUTER_APP_NAME"),
-		os.Getenv("OR_APP_NAME"),
+		inheritedName,
 		defaultInfronAppName,
 	)
 	return resolvedURL, resolvedName, true
diff --git a/sdk/go/ai/infron_attribution_test.go b/sdk/go/ai/infron_attribution_test.go
index 7454f5026..6070add6f 100644
--- a/sdk/go/ai/infron_attribution_test.go
+++ b/sdk/go/ai/infron_attribution_test.go
@@ -154,6 +154,7 @@ func TestInfronAttributionFallsBackToExistingVars(t *testing.T) {
 	t.Setenv("AGENTFIELD_INFRON_ATTRIBUTION", "")
 	t.Setenv("AGENTFIELD_INFRON_SITE_URL", "")
 	t.Setenv("AGENTFIELD_INFRON_APP_NAME", "")
+	t.Setenv("AGENTFIELD_OPENROUTER_ATTRIBUTION", "")
 	t.Setenv("AGENTFIELD_OPENROUTER_SITE_URL", "https://legacy.example")
 	t.Setenv("AGENTFIELD_OPENROUTER_APP_NAME", "Legacy App")
 
@@ -164,6 +165,27 @@ func TestInfronAttributionFallsBackToExistingVars(t *testing.T) {
 	assert.Equal(t, "Legacy App", header.Get("X-Title"))
 }
 
+// The opt-out travels with the inherited values: attribution a deployment
+// suppressed for OpenRouter — often because the site URL names an internal
+// host — must not be sent to a different vendor either. The Infron defaults
+// are used instead.
+func TestInfronAttributionDoesNotInheritOptedOutValues(t *testing.T) {
+	t.Setenv("AGENTFIELD_INFRON_ATTRIBUTION", "")
+	t.Setenv("AGENTFIELD_INFRON_SITE_URL", "")
+	t.Setenv("AGENTFIELD_INFRON_APP_NAME", "")
+	t.Setenv("AGENTFIELD_OPENROUTER_ATTRIBUTION", "false")
+	t.Setenv("AGENTFIELD_OPENROUTER_SITE_URL", "https://internal-tools.corp.example")
+	t.Setenv("AGENTFIELD_OPENROUTER_APP_NAME", "Internal Risk Engine")
+	t.Setenv("OR_SITE_URL", "")
+	t.Setenv("OR_APP_NAME", "")
+
+	header := http.Header{}
+	applyInfronAttributionHeaders(header, "", "")
+
+	assert.Equal(t, defaultInfronSiteURL, header.Get("HTTP-Referer"))
+	assert.Equal(t, defaultInfronAppName, header.Get("X-Title"))
+}
+
 func TestApplyInfronAttributionHeadersDisabled(t *testing.T) {
 	t.Setenv("AGENTFIELD_INFRON_ATTRIBUTION", "false")
 
@@ -290,14 +312,15 @@ func TestResponseNormalizesTopLevelCost(t *testing.T) {
 	assert.InDelta(t, 0.000002, *resp.Usage.Cost, 1e-12)
 }
 
-func TestResponseNormalizeCreatesUsageWhenAbsent(t *testing.T) {
+// A body carrying cost but no usage block must not have one fabricated for it:
+// a synthesized Usage carries zero token counts that downstream consumers read
+// as authoritative.
+func TestResponseNormalizeDoesNotFabricateUsage(t *testing.T) {
 	var resp Response
 	require.NoError(t, json.Unmarshal([]byte(`{"cost": 0.5}`), &resp))
 	resp.normalizeNativeCost()
 
-	require.NotNil(t, resp.Usage)
-	require.NotNil(t, resp.Usage.Cost)
-	assert.InDelta(t, 0.5, *resp.Usage.Cost, 1e-12)
+	assert.Nil(t, resp.Usage)
 }
 
 // An explicit usage.cost is authoritative and must not be overwritten.
@@ -347,3 +370,31 @@ func TestStreamChunkNormalizeNoopWithoutCost(t *testing.T) {
 
 	assert.Nil(t, chunk.Usage)
 }
+
+// A cost-only chunk must not grow a fabricated zero-token Usage. Stream
+// consumers accumulate last-usage-wins, so a synthesized Usage arriving after
+// the real usage chunk would erase the real token counts.
+func TestStreamChunkCostOnlyDoesNotFabricateUsage(t *testing.T) {
+	var usageChunk StreamChunk
+	require.NoError(t, json.Unmarshal(
+		[]byte(`{"usage": {"prompt_tokens": 10, "completion_tokens": 5, "total_tokens": 15}}`),
+		&usageChunk))
+	usageChunk.normalizeNativeCost()
+
+	var costChunk StreamChunk
+	require.NoError(t, json.Unmarshal([]byte(`{"cost": 0.00042, "choices": []}`), &costChunk))
+	costChunk.normalizeNativeCost()
+
+	assert.Nil(t, costChunk.Usage, "cost-only chunk must not synthesize usage")
+
+	// The last-usage-wins accumulation every stream consumer performs.
+	var accumulated *Usage
+	for _, chunk := range []StreamChunk{usageChunk, costChunk} {
+		if chunk.Usage != nil {
+			accumulated = chunk.Usage
+		}
+	}
+	require.NotNil(t, accumulated)
+	assert.Equal(t, 10, accumulated.PromptTokens)
+	assert.Equal(t, 5, accumulated.CompletionTokens)
+}
diff --git a/sdk/go/ai/response.go b/sdk/go/ai/response.go
index f76432df2..c48b9385c 100644
--- a/sdk/go/ai/response.go
+++ b/sdk/go/ai/response.go
@@ -29,13 +29,15 @@ type Response struct {
 // cost tracker reads as "price unknown" rather than "free" — usage is still
 // recorded, but silently with no cost and cost_source "" instead of
 // "provider". An explicit usage.cost always wins; this only fills a gap.
+//
+// The fold only happens into an existing usage block. Synthesizing one for a
+// cost-only body would fabricate zero token counts that downstream consumers
+// read as authoritative — on the streaming path a last-usage-wins accumulator
+// would let such a chunk erase real counts from an earlier chunk.
 func (r *Response) normalizeNativeCost() {
-	if r == nil || r.Cost == nil {
+	if r == nil || r.Cost == nil || r.Usage == nil {
 		return
 	}
-	if r.Usage == nil {
-		r.Usage = &Usage{}
-	}
 	if r.Usage.Cost == nil {
 		cost := *r.Cost
 		r.Usage.Cost = &cost
@@ -121,12 +123,9 @@ type StreamChunk struct {
 // normalizeNativeCost folds a top-level chunk cost into Usage.Cost. See
 // Response.normalizeNativeCost.
 func (s *StreamChunk) normalizeNativeCost() {
-	if s == nil || s.Cost == nil {
+	if s == nil || s.Cost == nil || s.Usage == nil {
 		return
 	}
-	if s.Usage == nil {
-		s.Usage = &Usage{}
-	}
 	if s.Usage.Cost == nil {
 		cost := *s.Cost
 		s.Usage.Cost = &cost