diff --git a/Makefile b/Makefile
index 007c749fc37..87e2b040447 100644
--- a/Makefile
+++ b/Makefile
@@ -13,6 +13,7 @@ FLOW ?=
 VERSION ?= dev-build
 LOCAL ?=
 DEBUG ?=
+COMPAT ?=
 
 # Colors for output
 RED=\033[0;31m
@@ -1771,6 +1772,21 @@ run-provider-harness-test: $(if $(HELP),,install-newman) ## Run the Bifrost prov
 		exit 0; \
 	fi
 	@if [ -n "$(HELP)" ]; then exit 0; fi; \
+	if [ "$(COMPAT)" = "both" ]; then \
+		mkdir -p tmp; \
+		$(ECHO) "$(CYAN)COMPAT=both: running harness with compat OFF then ON (sub-runs forced CI=1 to skip the interactive viewer)...$(NC)"; \
+		for mode in off on; do \
+			$(ECHO) "$(CYAN)=== Harness run: compat $$mode ===$(NC)"; \
+			$(MAKE) run-provider-harness-test COMPAT=$$mode CI=1; \
+			RC=$$?; \
+			mv -f tmp/newman-report.json "tmp/newman-report-compat-$$mode.json" 2>/dev/null || true; \
+			mv -f tmp/newman-report.html "tmp/newman-report-compat-$$mode.html" 2>/dev/null || true; \
+			mv -f tmp/harness-failures.md "tmp/harness-failures-compat-$$mode.md" 2>/dev/null || true; \
+			if [ "$$RC" -ne 0 ]; then $(ECHO) "$(RED)compat $$mode run failed (exit $$RC)$(NC)"; BOTH_RC=$$RC; fi; \
+		done; \
+		$(ECHO) "$(GREEN)COMPAT=both complete. Reports: tmp/newman-report-compat-{off,on}.{json,html}, tmp/harness-failures-compat-{off,on}.md$(NC)"; \
+		exit $${BOTH_RC:-0}; \
+	fi; \
 	$(EXPOSE_ENV); \
 	mkdir -p tmp; \
 	BASE_URL_VAL="$(or $(BASE_URL),http://localhost:8080)"; \
@@ -1893,6 +1909,7 @@ run-provider-harness-test: $(if $(HELP),,install-newman) ## Run the Bifrost prov
 			( \
 				newman run "tmp/harness-filtered-$$p.json" \
 					--env-var "baseUrl=$$BASE_URL_VAL" \
+					$(if $(filter on true 1 yes YES y Y,$(COMPAT)),--env-var "compat=true",) \
 					$(if $(filter 1 true TRUE yes YES y Y,$(INCLUDE_PREVIEW)),--env-var "include_preview=1",) \
 					$(if $(filter 1 true TRUE yes YES y Y,$(INCLUDE_SKIP)),--env-var "include_skip=1",) \
 					$${BEDROCK_GUARDRAIL_IDENTIFIER:+--env-var "bedrockGuardrailIdentifier=$$BEDROCK_GUARDRAIL_IDENTIFIER"} \
@@ -1975,6 +1992,7 @@ run-provider-harness-test: $(if $(HELP),,install-newman) ## Run the Bifrost prov
 			echo $$! > tmp/harness-monitor.pid; \
 			newman run "$$COLLECTION_FILE" \
 				--env-var "baseUrl=$$BASE_URL_VAL" \
+				$(if $(filter on true 1 yes YES y Y,$(COMPAT)),--env-var "compat=true",) \
 				$(if $(filter 1 true TRUE yes YES y Y,$(INCLUDE_PREVIEW)),--env-var "include_preview=1",) \
 				$(if $(filter 1 true TRUE yes YES y Y,$(INCLUDE_SKIP)),--env-var "include_skip=1",) \
 				$${BEDROCK_GUARDRAIL_IDENTIFIER:+--env-var "bedrockGuardrailIdentifier=$$BEDROCK_GUARDRAIL_IDENTIFIER"} \
@@ -1998,6 +2016,7 @@ run-provider-harness-test: $(if $(HELP),,install-newman) ## Run the Bifrost prov
 		else \
 			newman run "$$COLLECTION_FILE" \
 				--env-var "baseUrl=$$BASE_URL_VAL" \
+				$(if $(filter on true 1 yes YES y Y,$(COMPAT)),--env-var "compat=true",) \
 				$(if $(filter 1 true TRUE yes YES y Y,$(INCLUDE_PREVIEW)),--env-var "include_preview=1",) \
 				$(if $(filter 1 true TRUE yes YES y Y,$(INCLUDE_SKIP)),--env-var "include_skip=1",) \
 				$${BEDROCK_GUARDRAIL_IDENTIFIER:+--env-var "bedrockGuardrailIdentifier=$$BEDROCK_GUARDRAIL_IDENTIFIER"} \
diff --git a/framework/modelcatalog/datasheet/types.go b/framework/modelcatalog/datasheet/types.go
index 7b9fb16dddf..80aa5d71380 100644
--- a/framework/modelcatalog/datasheet/types.go
+++ b/framework/modelcatalog/datasheet/types.go
@@ -450,6 +450,8 @@ func extractSupportedParams(parsed *modelParametersParseResult) []string {
 		case "web_search":
 			addParam("web_search_options") // chat-path param
 			addParam("web_search")         // responses-path server tool
+		case "stop_sequences":
+			addParam("stop")
 		case "promptTools", "image_detail", "stream":
 			// skip — not top-level request parameters
 		default:
diff --git a/tests/e2e/api/collections/provider-harness.json b/tests/e2e/api/collections/provider-harness.json
index c6227a8190e..4e3f6067440 100644
--- a/tests/e2e/api/collections/provider-harness.json
+++ b/tests/e2e/api/collections/provider-harness.json
@@ -21,7 +21,11 @@
           "// Used in the criss-cross matrix (§8) to mark provider+modality cells that return NewUnsupportedOperationError by design (e.g., anthropic embeddings, bedrock audio).",
           "if (name.indexOf('[SKIP]') !== -1 && (pm.environment.get('include_skip') || pm.variables.get('include_skip') || '') !== '1') {",
           "  pm.execution.skipRequest();",
-          "}"
+          "}",
+          "// Per-request compat override: when compat is set (via Newman --env-var compat=true), inject the x-bf-compat header on every request.",
+          "// Absent => harness baseline (compat config off). Lets the suite run once with compat off and once with compat on.",
+          "var __compat = (pm.environment.get('compat') || pm.variables.get('compat') || '');",
+          "if (__compat) { pm.request.headers.upsert({ key: 'x-bf-compat', value: String(__compat) }); }"
         ]
       }
     },