diff --git a/bazel/rules/rules_score/private/assumed_system_requirements.bzl b/bazel/rules/rules_score/private/assumed_system_requirements.bzl
index 90ff590c..ec044f9c 100644
--- a/bazel/rules/rules_score/private/assumed_system_requirements.bzl
+++ b/bazel/rules/rules_score/private/assumed_system_requirements.bzl
@@ -51,8 +51,9 @@ def assumed_system_requirements(
         deps: Optional list of requirement targets whose TRLC records are needed
             for cross-reference parsing.  These targets must provide
             TrlcProviderInfo.  Typically empty for top-level system requirements.
-        spec: Optional TRLC specification target providing RSL type definitions.
-            Defaults to the S-CORE requirements model
+        spec: TRLC specification target(s) providing RSL type definitions.
+            Accepts a single label or a list of labels; all are merged into the
+            spec passed to TRLC.  Defaults to the S-CORE requirements model
             (``@score_tooling//bazel/rules/rules_score/trlc/config:score_requirements_model``).
             Override this when using a custom requirements model.
         lobster_config: Optional Lobster extraction config label. Defaults to the
diff --git a/bazel/rules/rules_score/private/component_requirements.bzl b/bazel/rules/rules_score/private/component_requirements.bzl
index 1ad91911..79a86b63 100644
--- a/bazel/rules/rules_score/private/component_requirements.bzl
+++ b/bazel/rules/rules_score/private/component_requirements.bzl
@@ -50,10 +50,10 @@ def component_requirements(
         deps: Optional list of requirement targets (e.g. assumed_system_requirements,
             feature_requirements) whose TRLC records are needed for cross-reference
             parsing.  These targets must provide TrlcProviderInfo.
-        spec: Optional TRLC specification target providing RSL type definitions.
-            Defaults to the S-CORE requirements model
+        spec: TRLC specification target(s) providing RSL type definitions.
+            Accepts a single label or a list of labels; all are merged into the
+            spec passed to TRLC.  Defaults to the S-CORE requirements model
             (``@score_tooling//bazel/rules/rules_score/trlc/config:score_requirements_model``).
-            Override this when using a custom requirements model.
         lobster_config: Optional Lobster extraction config label. Defaults to the
             S-CORE component requirement config.
         visibility: Bazel visibility specification for the generated targets.
diff --git a/bazel/rules/rules_score/private/feature_requirements.bzl b/bazel/rules/rules_score/private/feature_requirements.bzl
index f376fa0a..15adafbf 100644
--- a/bazel/rules/rules_score/private/feature_requirements.bzl
+++ b/bazel/rules/rules_score/private/feature_requirements.bzl
@@ -51,10 +51,10 @@ def feature_requirements(
         deps: Optional list of requirement targets (e.g. assumed_system_requirements)
             whose TRLC records are needed for cross-reference parsing.  These
             targets must provide TrlcProviderInfo.
-        spec: Optional TRLC specification target providing RSL type definitions.
-            Defaults to the S-CORE requirements model
+        spec: TRLC specification target(s) providing RSL type definitions.
+            Accepts a single label or a list of labels; all are merged into the
+            spec passed to TRLC.  Defaults to the S-CORE requirements model
             (``@score_tooling//bazel/rules/rules_score/trlc/config:score_requirements_model``).
-            Override this when using a custom requirements model.
         lobster_config: Optional Lobster extraction config label. Defaults to the
             S-CORE feature requirement config.
         visibility: Bazel visibility specification for the generated targets.
diff --git a/bazel/rules/rules_score/private/requirements.bzl b/bazel/rules/rules_score/private/requirements.bzl
index 621706af..415f0c1d 100644
--- a/bazel/rules/rules_score/private/requirements.bzl
+++ b/bazel/rules/rules_score/private/requirements.bzl
@@ -24,6 +24,8 @@ load("@trlc//:trlc.bzl", "TrlcProviderInfo", "subrule_trlc_image_stage")
 load("//bazel/rules/rules_score:providers.bzl", "AssumedSystemRequirementsInfo", "AssumptionsOfUseInfo", "ComponentRequirementsInfo", "FeatureRequirementsInfo", "SphinxSourcesInfo")
 load("//bazel/rules/rules_score/private:rst_to_trlc.bzl", "rst_to_trlc")
 
+_DEFAULT_SPEC = Label("//bazel/rules/rules_score/trlc/config:score_requirements_model")
+
 # ============================================================================
 # Private Rule Implementation
 # ============================================================================
@@ -50,7 +52,7 @@ def _requirements_impl(ctx):
         transitive_reqs.append(trlc_info.reqs)
         transitive_reqs.append(trlc_info.deps)
 
-    own_spec_files = ctx.attr.spec[DefaultInfo].files
+    own_spec_files = depset(transitive = [t[DefaultInfo].files for t in ctx.attr.spec])
     spec_depset = depset(transitive = [own_spec_files] + transitive_spec)
     deps_depset = depset(transitive = transitive_reqs)
 
@@ -167,9 +169,9 @@ _score_requirements_rule = rule(
             mandatory = True,
             doc = "Lobster YAML configuration file for traceability extraction.",
         ),
-        "spec": attr.label(
-            default = Label("//bazel/rules/rules_score/trlc/config:score_requirements_model"),
-            doc = "TRLC specification target providing the RSL files that define the requirement types. Defaults to the S-CORE requirements model.",
+        "spec": attr.label_list(
+            default = [_DEFAULT_SPEC],
+            doc = "TRLC specification targets providing the RSL files that define the requirement types. The S-CORE requirements model is always included; this adds zero or more additional spec targets on top of it. Populated by the score_requirements_rule macro, which performs the merge.",
         ),
         "image_srcs": attr.label_list(
             allow_files = [".svg", ".png", ".puml"],
@@ -192,7 +194,7 @@ def score_requirements_rule(
         req_kind,
         lobster_config,
         deps = [],
-        spec = Label("//bazel/rules/rules_score/trlc/config:score_requirements_model"),
+        spec = [],
         ref_package = "",
         **kwargs):
     """Macro wrapper around _score_requirements_rule with RST support.
@@ -207,6 +209,9 @@ def score_requirements_rule(
         listed in the underlying rule's ``srcs``.
 
     Args:
+        spec: Additional TRLC specification target(s) (single label or list)
+            to merge in on top of the S-CORE requirements model, which is
+            always included automatically -- do not re-list it here.
         ref_package: TRLC package prefix used for derived_from cross-references
             when converting RST sources (e.g. "AssumedSystemRequirements" for
             feature requirements that derive from ASR).
@@ -216,6 +221,8 @@ def score_requirements_rule(
         conversion), in the same order. Useful for callers that need to run
         trlc_requirements_test against the same source set.
     """
+    extra_spec = spec if type(spec) == type([]) else [spec]
+    merged_spec = [_DEFAULT_SPEC] + [s for s in extra_spec if s != _DEFAULT_SPEC]
     trlc_srcs = []
     extra_deps = []
     resolved_srcs = []
@@ -242,7 +249,7 @@ def score_requirements_rule(
         deps = deps + extra_deps,
         req_kind = req_kind,
         lobster_config = lobster_config,
-        spec = spec,
+        spec = merged_spec,
         **kwargs
     )
 
diff --git a/bazel/rules/rules_score/test/BUILD b/bazel/rules/rules_score/test/BUILD
index ff470fcd..7f45ded6 100644
--- a/bazel/rules/rules_score/test/BUILD
+++ b/bazel/rules/rules_score/test/BUILD
@@ -13,6 +13,8 @@
 
 load("@pip_tooling_test//:requirements.bzl", "requirement")
 load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library", "cc_test")
+load("@rules_python//python:defs.bzl", "py_test")
+load("@rules_shell//shell:sh_test.bzl", "sh_test")
 load(
     "@score_tooling//bazel/rules/rules_score:rules_score.bzl",
     "architectural_design",
@@ -30,7 +32,7 @@ load(
 )
 load("@score_tooling//bazel/rules/rules_score:sphinx_toolchain.bzl", "score_sphinx_toolchain")
 load("@score_tooling//cpp/libclang:libclang_toolchain.bzl", "libclang_toolchain")
-load("@trlc//:trlc.bzl", "trlc_requirements", "trlc_requirements_test")
+load("@trlc//:trlc.bzl", "trlc_requirements", "trlc_requirements_test", "trlc_specification")
 load(
     ":html_generation_test.bzl",
     "auto_config_generation_test",
@@ -48,9 +50,11 @@ load(
     "lobster_config_test_suite",
 )
 load(
-    ":requirements_image_test.bzl",
-    "image_srcs_sphinx_sources_test",
-    "requirements_image_test_suite",
+    ":requirements_multi_spec_test.bzl",
+    "asr_multi_spec_provider_test",
+    "comp_req_multi_spec_provider_test",
+    "feat_req_multi_spec_provider_test",
+    "requirements_multi_spec_test_suite",
 )
 load(
     ":requirements_rst_test.bzl",
@@ -1369,6 +1373,65 @@ aous_rst_sphinx_test(
 
 requirements_rst_test_suite(name = "requirements_rst_tests")
 
+# ============================================================================
+# Multi-spec Requirements Tests
+# ============================================================================
+
+trlc_specification(
+    name = "extra_spec_fixture",
+    srcs = ["fixtures/multi_spec/extra_model.rsl"],
+)
+
+assumed_system_requirements(
+    name = "asr_multi_spec",
+    srcs = ["fixtures/rst_requirements/assumed_system_requirements.rst"],
+    spec = [":extra_spec_fixture"],
+)
+
+feature_requirements(
+    name = "feat_req_multi_spec",
+    srcs = ["fixtures/rst_requirements/feature_requirements.rst"],
+    ref_package = "AssumedSystemRequirements",
+    spec = [":extra_spec_fixture"],
+    deps = [":asr_multi_spec"],
+)
+
+component_requirements(
+    name = "comp_req_multi_spec",
+    srcs = ["fixtures/rst_requirements/component_requirements.rst"],
+    ref_package = "FeatureRequirements",
+    spec = [":extra_spec_fixture"],
+    deps = [
+        ":asr_multi_spec",
+        ":feat_req_multi_spec",
+    ],
+)
+
+asr_multi_spec_provider_test(
+    name = "asr_multi_spec_provider_test",
+    target_under_test = ":asr_multi_spec",
+)
+
+feat_req_multi_spec_provider_test(
+    name = "feat_req_multi_spec_provider_test",
+    target_under_test = ":feat_req_multi_spec",
+)
+
+comp_req_multi_spec_provider_test(
+    name = "comp_req_multi_spec_provider_test",
+    target_under_test = ":comp_req_multi_spec",
+)
+
+# Integration target: TRLC file using types from both specs; trlc --verify
+# runs on build, confirming both RSL files are reachable at parse time.
+assumed_system_requirements(
+    name = "asr_multi_spec_inttest",
+    srcs = ["fixtures/multi_spec/multi_spec.trlc"],
+    spec = [":extra_spec_fixture"],
+)
+
+requirements_multi_spec_test_suite(name = "requirements_multi_spec_tests")
+
 # ============================================================================
 # lobster_config.bzl unit tests (format_lobster_sources / format_lobster_block)
 # ============================================================================
@@ -1464,6 +1527,7 @@ test_suite(
     name = "all_tests",
     tests = [
         ":lobster_config_tests",
+        ":requirements_multi_spec_tests",
         ":requirements_rst_tests",
         ":seooc_tests",
         ":sphinx_module_tests",
diff --git a/bazel/rules/rules_score/test/fixtures/multi_spec/extra_model.rsl b/bazel/rules/rules_score/test/fixtures/multi_spec/extra_model.rsl
new file mode 100644
index 00000000..50739d6e
--- /dev/null
+++ b/bazel/rules/rules_score/test/fixtures/multi_spec/extra_model.rsl
@@ -0,0 +1,22 @@
+/********************************************************************************
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Apache License Version 2.0 which is available at
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ ********************************************************************************/
+
+// Project-specific model extension (fixture for multi-spec tests).
+// Uses a distinct package name — TRLC does not allow two RSL files with the
+// same package declaration.
+package ProjectReq
+
+type ProjectNote "A project-specific note for internal tracking." {
+    description "Note content."
+                String
+}
diff --git a/bazel/rules/rules_score/test/fixtures/multi_spec/multi_spec.trlc b/bazel/rules/rules_score/test/fixtures/multi_spec/multi_spec.trlc
new file mode 100644
index 00000000..dbeb5bb7
--- /dev/null
+++ b/bazel/rules/rules_score/test/fixtures/multi_spec/multi_spec.trlc
@@ -0,0 +1,31 @@
+/********************************************************************************
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Apache License Version 2.0 which is available at
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ ********************************************************************************/
+
+// Integration fixture: uses AssumedSystemReq (base model) and ProjectNote
+// (extra model) in one file to verify that both RSL files are reachable when
+// spec is passed as a list.
+package MultiSpecIntTest
+
+import ScoreReq
+import ProjectReq
+
+ScoreReq.AssumedSystemReq asr_multi_spec_inttest_001 {
+    description = "The system shall support multi-spec requirements models."
+    safety      = ScoreReq.Asil.B
+    version     = 1
+    rationale   = "Validates that the base spec types are accessible when spec is a list."
+}
+
+ProjectReq.ProjectNote note_multi_spec_inttest_001 {
+    description = "Validates that a type from the extra spec is accessible alongside the base model."
+}
diff --git a/bazel/rules/rules_score/test/fixtures/spec_extras/BUILD b/bazel/rules/rules_score/test/fixtures/spec_extras/BUILD
new file mode 100644
index 00000000..844c86bb
--- /dev/null
+++ b/bazel/rules/rules_score/test/fixtures/spec_extras/BUILD
@@ -0,0 +1,28 @@
+# *******************************************************************************
+# Copyright (c) 2026 Contributors to the Eclipse Foundation
+#
+# See the NOTICE file(s) distributed with this work for additional
+# information regarding copyright ownership.
+#
+# This program and the accompanying materials are made available under the
+# terms of the Apache License Version 2.0 which is available at
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# SPDX-License-Identifier: Apache-2.0
+# *******************************************************************************
+
+load("@score_tooling//bazel/rules/rules_score:rules_score.bzl", "component_requirements")
+load("@trlc//:trlc.bzl", "trlc_specification")
+
+package(default_visibility = ["//visibility:public"])
+
+trlc_specification(
+    name = "extra_spec",
+    srcs = ["extra_model.rsl"],
+)
+
+component_requirements(
+    name = "spec_extras_comp_req",
+    srcs = ["project_requirements.trlc"],
+    spec_extras = [":extra_spec"],
+)
diff --git a/bazel/rules/rules_score/test/fixtures/spec_extras/extra_model.rsl b/bazel/rules/rules_score/test/fixtures/spec_extras/extra_model.rsl
new file mode 100644
index 00000000..0abb20ad
--- /dev/null
+++ b/bazel/rules/rules_score/test/fixtures/spec_extras/extra_model.rsl
@@ -0,0 +1,19 @@
+/********************************************************************************
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Apache License Version 2.0 which is available at
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ ********************************************************************************/
+
+package ExtraModel
+import ScoreReq
+
+type ProjectSpecificReq extends ScoreReq.CompReq {
+    project_id "Project identifier" String
+}
diff --git a/bazel/rules/rules_score/test/fixtures/spec_extras/project_requirements.trlc b/bazel/rules/rules_score/test/fixtures/spec_extras/project_requirements.trlc
new file mode 100644
index 00000000..4decca6b
--- /dev/null
+++ b/bazel/rules/rules_score/test/fixtures/spec_extras/project_requirements.trlc
@@ -0,0 +1,32 @@
+/********************************************************************************
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Apache License Version 2.0 which is available at
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ ********************************************************************************/
+
+package TestFixtures
+
+import ExtraModel
+import ScoreReq
+
+ScoreReq.AssumedSystemReq ASR_TEST_001 {
+    description = "Input system-level requirement for spec_extras test"
+    rationale = "Needed to satisfy derived_from constraints"
+    safety = ScoreReq.Asil.B
+    version = 1
+}
+
+ExtraModel.ProjectSpecificReq PROJ_REQ_001 {
+    description = "Requirement using a type from spec_extras."
+    safety = ScoreReq.Asil.B
+    derived_from = [ASR_TEST_001@1]
+    version = 1
+    project_id = "TEST"
+}
diff --git a/bazel/rules/rules_score/test/requirements_multi_spec_test.bzl b/bazel/rules/rules_score/test/requirements_multi_spec_test.bzl
new file mode 100644
index 00000000..21ab4e9f
--- /dev/null
+++ b/bazel/rules/rules_score/test/requirements_multi_spec_test.bzl
@@ -0,0 +1,112 @@
+# *******************************************************************************
+# Copyright (c) 2026 Contributors to the Eclipse Foundation
+#
+# See the NOTICE file(s) distributed with this work for additional
+# information regarding copyright ownership.
+#
+# This program and the accompanying materials are made available under the
+# terms of the Apache License Version 2.0 which is available at
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# SPDX-License-Identifier: Apache-2.0
+# *******************************************************************************
+"""
+Tests that requirement macros accept a list of labels for ``spec``.
+
+Verifies that assumed_system_requirements, feature_requirements, and
+component_requirements all produce their expected providers when spec is
+passed as a list of two labels.
+"""
+
+load("@bazel_skylib//lib:unittest.bzl", "analysistest", "asserts")
+load(
+    "@score_tooling//bazel/rules/rules_score:providers.bzl",
+    "AssumedSystemRequirementsInfo",
+    "ComponentRequirementsInfo",
+    "FeatureRequirementsInfo",
+    "SphinxSourcesInfo",
+)
+
+# ============================================================================
+# assumed_system_requirements – list spec
+# ============================================================================
+
+def _asr_multi_spec_provider_test_impl(ctx):
+    env = analysistest.begin(ctx)
+    target_under_test = analysistest.target_under_test(env)
+    asserts.true(
+        env,
+        AssumedSystemRequirementsInfo in target_under_test,
+        "assumed_system_requirements with list spec should provide AssumedSystemRequirementsInfo",
+    )
+    asserts.true(
+        env,
+        SphinxSourcesInfo in target_under_test,
+        "assumed_system_requirements with list spec should provide SphinxSourcesInfo",
+    )
+    return analysistest.end(env)
+
+asr_multi_spec_provider_test = analysistest.make(_asr_multi_spec_provider_test_impl)
+
+# ============================================================================
+# feature_requirements – list spec
+# ============================================================================
+
+def _feat_req_multi_spec_provider_test_impl(ctx):
+    env = analysistest.begin(ctx)
+    target_under_test = analysistest.target_under_test(env)
+    asserts.true(
+        env,
+        FeatureRequirementsInfo in target_under_test,
+        "feature_requirements with list spec should provide FeatureRequirementsInfo",
+    )
+    asserts.true(
+        env,
+        SphinxSourcesInfo in target_under_test,
+        "feature_requirements with list spec should provide SphinxSourcesInfo",
+    )
+    return analysistest.end(env)
+
+feat_req_multi_spec_provider_test = analysistest.make(_feat_req_multi_spec_provider_test_impl)
+
+# ============================================================================
+# component_requirements – list spec
+# ============================================================================
+
+def _comp_req_multi_spec_provider_test_impl(ctx):
+    env = analysistest.begin(ctx)
+    target_under_test = analysistest.target_under_test(env)
+    asserts.true(
+        env,
+        ComponentRequirementsInfo in target_under_test,
+        "component_requirements with list spec should provide ComponentRequirementsInfo",
+    )
+    asserts.true(
+        env,
+        SphinxSourcesInfo in target_under_test,
+        "component_requirements with list spec should provide SphinxSourcesInfo",
+    )
+    return analysistest.end(env)
+
+comp_req_multi_spec_provider_test = analysistest.make(_comp_req_multi_spec_provider_test_impl)
+
+# ============================================================================
+# Test Suite
+# ============================================================================
+
+def requirements_multi_spec_test_suite(name):
+    """Register all multi-spec requirement tests.
+
+    Args:
+        name: Name for the test_suite target.
+    """
+    native.test_suite(
+        name = name,
+        tests = [
+            ":asr_multi_spec_provider_test",
+            ":feat_req_multi_spec_provider_test",
+            ":comp_req_multi_spec_provider_test",
+            # Integration test: trlc --verify with both RSL files actually loaded
+            ":asr_multi_spec_inttest_test",
+        ],
+    )
diff --git a/bazel/rules/rules_score/test/requirements_spec_extras_test.bzl b/bazel/rules/rules_score/test/requirements_spec_extras_test.bzl
new file mode 100644
index 00000000..e26aeaee
--- /dev/null
+++ b/bazel/rules/rules_score/test/requirements_spec_extras_test.bzl
@@ -0,0 +1,46 @@
+# *******************************************************************************
+# Copyright (c) 2026 Contributors to the Eclipse Foundation
+#
+# See the NOTICE file(s) distributed with this work for additional
+# information regarding copyright ownership.
+#
+# This program and the accompanying materials are made available under the
+# terms of the Apache License Version 2.0 which is available at
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# SPDX-License-Identifier: Apache-2.0
+# *******************************************************************************
+
+"""Analysis tests for spec_extras support in requirements macros."""
+
+load("@bazel_skylib//lib:unittest.bzl", "analysistest", "asserts")
+load("@trlc//:trlc.bzl", "TrlcProviderInfo")
+
+def _spec_extras_in_provider_test_impl(ctx):
+    env = analysistest.begin(ctx)
+    target_under_test = analysistest.target_under_test(env)
+
+    spec_basenames = [f.basename for f in target_under_test[TrlcProviderInfo].spec.to_list()]
+
+    asserts.true(
+        env,
+        "score_requirements_model.rsl" in spec_basenames,
+        "Base score spec should still be present in TrlcProviderInfo.spec",
+    )
+    asserts.true(
+        env,
+        "extra_model.rsl" in spec_basenames,
+        "spec_extras RSL should be merged into TrlcProviderInfo.spec",
+    )
+
+    return analysistest.end(env)
+
+spec_extras_in_provider_test = analysistest.make(_spec_extras_in_provider_test_impl)
+
+def requirements_spec_extras_test_suite(name):
+    native.test_suite(
+        name = name,
+        tests = [
+            ":spec_extras_in_provider_test",
+        ],
+    )