From a3df0be9b7e69d92fac176661d7c95b482d35fb6 Mon Sep 17 00:00:00 2001
From: Mikayla Toffler <mikayla.toffler@datadoghq.com>
Date: Thu, 1 Oct 2026 13:35:32 -0400
Subject: [PATCH 01/12] fix(remote-config): support restored Node.js capability
 bits

---
 tests/parametric/capabilities.yml             |  9 +++---
 .../parametric/test_dynamic_configuration.py  | 16 +++++------
 tests/test_the_test/test_remote_config.py     | 20 +++++++++++--
 utils/_remote_config.py                       | 28 +++++++++++++------
 4 files changed, 50 insertions(+), 23 deletions(-)

diff --git a/tests/parametric/capabilities.yml b/tests/parametric/capabilities.yml
index 2218c856d7c..26b98ded803 100644
--- a/tests/parametric/capabilities.yml
+++ b/tests/parametric/capabilities.yml
@@ -70,8 +70,9 @@ capabilities:
       - ASM_AUTO_USER_INSTRUM_MODE
 
     # SDK_CONFIGURATION supersedes the per-setting APM_TRACING capabilities in the 5.x
-    # line from 5.128.0 and in the 6.x line from 6.17.0.
-    '<5.128.0 || >=6.0.0-0 <6.17.0':
+    # line from 5.128.0 and in the 6.x line from 6.17.0. Node.js 6.19.0 restores the
+    # legacy bits as compatibility metadata while continuing to consume sdk_config.
+    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
       - APM_TRACING_CUSTOM_TAGS
       - APM_TRACING_ENABLED
       - APM_TRACING_HTTP_HEADER_TAGS
@@ -88,11 +89,11 @@ capabilities:
     '>=5.83.0':
       - APM_TRACING_MULTICONFIG
 
-    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0':
+    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
       - APM_TRACING_ENABLE_CODE_ORIGIN
       - APM_TRACING_ENABLE_DYNAMIC_INSTRUMENTATION
 
-    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0':
+    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
       - APM_TRACING_ENABLE_LIVE_DEBUGGING
 
   python:
diff --git a/tests/parametric/test_dynamic_configuration.py b/tests/parametric/test_dynamic_configuration.py
index 215d81a21e2..d25ee305009 100644
--- a/tests/parametric/test_dynamic_configuration.py
+++ b/tests/parametric/test_dynamic_configuration.py
@@ -193,10 +193,10 @@ def uses_sdk_configuration(test_agent: TestAgentAPI) -> bool:
 def assert_rc_capability(test_agent: TestAgentAPI, capability: Capabilities, wait_loops: int = 100) -> None:
     """Assert that the tracer advertises the capability to remotely configure one setting.
 
-    A tracer that has moved to the unified SDK_CONFIGURATION contract advertises that single bit
-    for every remotely configurable setting instead of the per-setting ones, so it stands in for
-    any of them. The SDK_CONFIGURATION bit on its own does not, since libdatadog gives that bit a
-    different meaning; only a tracer that has really dropped the per-setting bits qualifies.
+    A tracer that has moved to the unified SDK_CONFIGURATION contract can use that bit for every
+    remotely configurable setting, so it stands in for any missing per-setting one. The
+    SDK_CONFIGURATION bit on its own does not, since libdatadog gives that bit a different meaning;
+    only a tracer whose capability combination identifies the unified contract qualifies.
     """
     seen_capabilities = test_agent.wait_for_rc_capabilities(wait_loops)
     if capability in seen_capabilities:
@@ -581,10 +581,10 @@ def test_tracing_client_tracing_disable_one_way(
 class Test_DynamicConfigSdkConfiguration:
     """Coverage for the generic sdk_config RC delivery path.
 
-    sdk_config carries settings as generic env-var-keyed entries, applied via the single
-    SDK_CONFIGURATION capability instead of custom per-setting parsing. These tests confirm a
-    tracer that declares SDK_CONFIGURATION consumes sdk_config with no regression in behavior
-    compared to the equivalent lib_config delivery, starting with DD_TRACE_ENABLED.
+    sdk_config carries settings as generic env-var-keyed entries, applied via the unified
+    SDK_CONFIGURATION contract instead of custom per-setting parsing. These tests confirm a tracer
+    on that contract consumes sdk_config with no regression in behavior compared to the equivalent
+    lib_config delivery, starting with DD_TRACE_ENABLED.
 
     test_sdk_config_tracing_enabled_matches_lib_config asserts real behavior (tracing actually
     stops) for DD_TRACE_ENABLED. test_sdk_config_field_is_applied then layers a shallower
diff --git a/tests/test_the_test/test_remote_config.py b/tests/test_the_test/test_remote_config.py
index b68bc157780..4d69d0718a7 100644
--- a/tests/test_the_test/test_remote_config.py
+++ b/tests/test_the_test/test_remote_config.py
@@ -196,9 +196,10 @@ def test_resolve_sdk_configuration_contract():
     """The SDK_CONFIGURATION bit alone does not mean the library reads sdk_config.
 
     Bit 49 is SDK_CONFIGURATION in the remote config source of truth, but libdatadog gives the
-    same bit to ASM_RAW_RESPONSE_BODY, so the per-setting capabilities have to be gone too.
+    same bit to ASM_RAW_RESPONSE_BODY. Capability interpretation therefore also needs to account
+    for the tracer implementation when legacy bits and SDK_CONFIGURATION appear together.
     """
-    # dd-trace-js with the SDK_CONFIGURATION support: the per-setting capabilities are dropped
+    # dd-trace-js 6.17.0 and 6.18.0: the per-setting capabilities are dropped
     assert rc.resolve_sdk_configuration_contract(
         {
             Capabilities.ASM_ACTIVATION,
@@ -224,6 +225,21 @@ def test_resolve_sdk_configuration_contract():
         is False
     )
 
+    # dd-trace-js 6.19.0+: legacy bits are compatibility metadata, but sdk_config remains the
+    # only application path. The same capability combination still means lib_config for PHP.
+    mixed_capabilities = {
+        Capabilities.APM_TRACING_CUSTOM_TAGS,
+        Capabilities.APM_TRACING_ENABLED,
+        Capabilities.APM_TRACING_HTTP_HEADER_TAGS,
+        Capabilities.APM_TRACING_LOGS_INJECTION,
+        Capabilities.APM_TRACING_SAMPLE_RATE,
+        Capabilities.APM_TRACING_SAMPLE_RULES,
+        Capabilities.APM_TRACING_MULTICONFIG,
+        Capabilities.SDK_CONFIGURATION,
+    }
+    assert rc.resolve_sdk_configuration_contract(mixed_capabilities, library_name="nodejs") is True
+    assert rc.resolve_sdk_configuration_contract(mixed_capabilities, library_name="php") is False
+
     # dd-trace-java: no SDK_CONFIGURATION at all
     assert (
         rc.resolve_sdk_configuration_contract({Capabilities.APM_TRACING_SAMPLE_RATE, Capabilities.APM_TRACING_ENABLED})
diff --git a/utils/_remote_config.py b/utils/_remote_config.py
index 77309523b80..c1e55408545 100644
--- a/utils/_remote_config.py
+++ b/utils/_remote_config.py
@@ -645,8 +645,9 @@ def to_sdk_config_payload(config: dict[str, Any]) -> dict[str, Any]:
     capability for capability in Capabilities if capability.name.startswith("APM_TRACING_")
 )
 
-# The per-setting APM_TRACING capabilities that SDK_CONFIGURATION replaces. A library on the new
-# contract advertises the single SDK_CONFIGURATION bit instead of all of these.
+# The per-setting APM_TRACING capabilities that SDK_CONFIGURATION originally replaced. Most
+# libraries on the new contract advertise the single SDK_CONFIGURATION bit instead of these;
+# Node.js 6.19.0+ advertises both for backend/frontend compatibility while consuming sdk_config.
 LEGACY_APM_TRACING_CAPABILITIES = frozenset(
     {
         Capabilities.APM_TRACING_CUSTOM_TAGS,
@@ -659,7 +660,9 @@ def to_sdk_config_payload(config: dict[str, Any]) -> dict[str, Any]:
 )
 
 
-def resolve_sdk_configuration_contract(capabilities: set[Capabilities]) -> bool | None:
+def resolve_sdk_configuration_contract(
+    capabilities: set[Capabilities], *, library_name: str | None = None
+) -> bool | None:
     """Decide which APM_TRACING payload shape a set of advertised capabilities asks for.
 
     Returns True for `sdk_config`, False for `lib_config`, and None when the capabilities seen so
@@ -670,15 +673,22 @@ def resolve_sdk_configuration_contract(capabilities: set[Capabilities]) -> bool
     libdatadog hands the same bit to `ASM_RAW_RESPONSE_BODY`, so a libdatadog-based library such as
     dd-trace-php advertises it while still reading `lib_config`.
 
-    Dropping the per-setting capabilities is the whole point of the unified bit, so their absence
-    is what distinguishes the two. Absence only counts once the library has actually registered its
-    APM_TRACING remote config, though: capabilities are added as products start, and AppSec ones
-    come first, so an early poll from a libdatadog library shows bit 49 with no APM_TRACING bit yet
-    and would otherwise be mistaken for the unified contract.
+    For Node.js, SDK_CONFIGURATION is authoritative even when the legacy per-setting bits are also
+    present. Node.js 6.19.0 restored those bits for backend/frontend compatibility without restoring
+    the legacy `lib_config` application path.
+
+    For other tracers, dropping the per-setting capabilities is what distinguishes the two. Absence
+    only counts once the library has actually registered its APM_TRACING remote config, though:
+    capabilities are added as products start, and AppSec ones come first, so an early poll from a
+    libdatadog library shows bit 49 with no APM_TRACING bit yet and would otherwise be mistaken for
+    the unified contract.
     """
     if not capabilities & APM_TRACING_CAPABILITIES:
         return None
 
+    if library_name == "nodejs" and Capabilities.SDK_CONFIGURATION in capabilities:
+        return True
+
     if capabilities & LEGACY_APM_TRACING_CAPABILITIES:
         return False
 
@@ -711,7 +721,7 @@ def resolve_sdk_configuration_support(get_capabilities: Callable[[], set[Capabil
         logger.error(f"Could not read the RC capabilities ({e}), assuming no SDK_CONFIGURATION support")
         return False
 
-    supported = resolve_sdk_configuration_contract(capabilities)
+    supported = resolve_sdk_configuration_contract(capabilities, library_name=context.library.name)
     if supported is None:
         logger.info("No APM_TRACING capability advertised yet, sending lib_config for now")
         return False

From 3d430f1fa885b7c372a2b5fde5432d793526f250 Mon Sep 17 00:00:00 2001
From: Mikayla Toffler <mikayla.toffler@datadoghq.com>
Date: Thu, 1 Oct 2026 13:45:37 -0400
Subject: [PATCH 02/12] fix(nodejs): scope restored capabilities to 6.x

---
 tests/parametric/capabilities.yml | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tests/parametric/capabilities.yml b/tests/parametric/capabilities.yml
index 26b98ded803..c2e00568a52 100644
--- a/tests/parametric/capabilities.yml
+++ b/tests/parametric/capabilities.yml
@@ -71,8 +71,9 @@ capabilities:
 
     # SDK_CONFIGURATION supersedes the per-setting APM_TRACING capabilities in the 5.x
     # line from 5.128.0 and in the 6.x line from 6.17.0. Node.js 6.19.0 restores the
-    # legacy bits as compatibility metadata while continuing to consume sdk_config.
-    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
+    # legacy bits as compatibility metadata while continuing to consume sdk_config. Keep the
+    # restored-bit range below 7.0.0: the main branch reports 7.0.0-pre before this change lands.
+    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0 <7.0.0-0':
       - APM_TRACING_CUSTOM_TAGS
       - APM_TRACING_ENABLED
       - APM_TRACING_HTTP_HEADER_TAGS
@@ -89,11 +90,11 @@ capabilities:
     '>=5.83.0':
       - APM_TRACING_MULTICONFIG
 
-    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
+    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0 <7.0.0-0':
       - APM_TRACING_ENABLE_CODE_ORIGIN
       - APM_TRACING_ENABLE_DYNAMIC_INSTRUMENTATION
 
-    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
+    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0 <7.0.0-0':
       - APM_TRACING_ENABLE_LIVE_DEBUGGING
 
   python:

From 477b105da433e106ca070d4e2b203a3ee13eb379 Mon Sep 17 00:00:00 2001
From: Mikayla Toffler <mikayla.toffler@datadoghq.com>
Date: Thu, 1 Oct 2026 14:26:19 -0400
Subject: [PATCH 03/12] refactor(remote-config): clarify lib config capability
 fingerprint

---
 tests/test_the_test/test_remote_config.py |  2 +-
 utils/_remote_config.py                   | 13 +++++++------
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/tests/test_the_test/test_remote_config.py b/tests/test_the_test/test_remote_config.py
index 4d69d0718a7..5f9b2bc62d4 100644
--- a/tests/test_the_test/test_remote_config.py
+++ b/tests/test_the_test/test_remote_config.py
@@ -281,5 +281,5 @@ def test_apm_tracing_capabilities_exclude_sdk_configuration():
     `resolve_sdk_configuration_contract`.
     """
     assert Capabilities.SDK_CONFIGURATION not in rc.APM_TRACING_CAPABILITIES
-    assert rc.LEGACY_APM_TRACING_CAPABILITIES <= rc.APM_TRACING_CAPABILITIES
+    assert rc.LIB_CONFIG_CAPABILITY_FINGERPRINT <= rc.APM_TRACING_CAPABILITIES
     assert Capabilities.APM_TRACING_MULTICONFIG in rc.APM_TRACING_CAPABILITIES
diff --git a/utils/_remote_config.py b/utils/_remote_config.py
index c1e55408545..087be24c9c5 100644
--- a/utils/_remote_config.py
+++ b/utils/_remote_config.py
@@ -645,10 +645,11 @@ def to_sdk_config_payload(config: dict[str, Any]) -> dict[str, Any]:
     capability for capability in Capabilities if capability.name.startswith("APM_TRACING_")
 )
 
-# The per-setting APM_TRACING capabilities that SDK_CONFIGURATION originally replaced. Most
-# libraries on the new contract advertise the single SDK_CONFIGURATION bit instead of these;
-# Node.js 6.19.0+ advertises both for backend/frontend compatibility while consuming sdk_config.
-LEGACY_APM_TRACING_CAPABILITIES = frozenset(
+# The per-setting capability fingerprint observed on libraries that consume `lib_config`. This is
+# deliberately not an exhaustive set of legacy APM_TRACING capabilities: optional feature bits do
+# not reliably identify the payload contract. Node.js 6.19.0+ re-advertises this fingerprint for
+# backend/frontend compatibility while continuing to consume `sdk_config`.
+LIB_CONFIG_CAPABILITY_FINGERPRINT = frozenset(
     {
         Capabilities.APM_TRACING_CUSTOM_TAGS,
         Capabilities.APM_TRACING_ENABLED,
@@ -677,7 +678,7 @@ def resolve_sdk_configuration_contract(
     present. Node.js 6.19.0 restored those bits for backend/frontend compatibility without restoring
     the legacy `lib_config` application path.
 
-    For other tracers, dropping the per-setting capabilities is what distinguishes the two. Absence
+    For other tracers, the per-setting fingerprint distinguishes the two contracts. Its absence
     only counts once the library has actually registered its APM_TRACING remote config, though:
     capabilities are added as products start, and AppSec ones come first, so an early poll from a
     libdatadog library shows bit 49 with no APM_TRACING bit yet and would otherwise be mistaken for
@@ -689,7 +690,7 @@ def resolve_sdk_configuration_contract(
     if library_name == "nodejs" and Capabilities.SDK_CONFIGURATION in capabilities:
         return True
 
-    if capabilities & LEGACY_APM_TRACING_CAPABILITIES:
+    if capabilities & LIB_CONFIG_CAPABILITY_FINGERPRINT:
         return False
 
     return Capabilities.SDK_CONFIGURATION in capabilities

From d8aae2e952970b074763508df7348e245b13bf52 Mon Sep 17 00:00:00 2001
From: Mikayla Toffler <mikayla.toffler@datadoghq.com>
Date: Thu, 1 Oct 2026 14:28:55 -0400
Subject: [PATCH 04/12] test(remote-config): model exact Node capability set

---
 tests/test_the_test/test_remote_config.py | 35 +++++++++--------------
 1 file changed, 13 insertions(+), 22 deletions(-)

diff --git a/tests/test_the_test/test_remote_config.py b/tests/test_the_test/test_remote_config.py
index 5f9b2bc62d4..951a825172c 100644
--- a/tests/test_the_test/test_remote_config.py
+++ b/tests/test_the_test/test_remote_config.py
@@ -208,26 +208,9 @@ def test_resolve_sdk_configuration_contract():
         }
     )
 
-    # dd-trace-php: bit 49 is ASM_RAW_RESPONSE_BODY there, and lib_config is still what it reads
-    assert (
-        rc.resolve_sdk_configuration_contract(
-            {
-                Capabilities.APM_TRACING_CUSTOM_TAGS,
-                Capabilities.APM_TRACING_ENABLED,
-                Capabilities.APM_TRACING_HTTP_HEADER_TAGS,
-                Capabilities.APM_TRACING_LOGS_INJECTION,
-                Capabilities.APM_TRACING_SAMPLE_RATE,
-                Capabilities.APM_TRACING_SAMPLE_RULES,
-                Capabilities.APM_TRACING_MULTICONFIG,
-                Capabilities.SDK_CONFIGURATION,
-            }
-        )
-        is False
-    )
-
-    # dd-trace-js 6.19.0+: legacy bits are compatibility metadata, but sdk_config remains the
-    # only application path. The same capability combination still means lib_config for PHP.
-    mixed_capabilities = {
+    # dd-trace-php: bit 49 is ASM_RAW_RESPONSE_BODY there, and the per-setting fingerprint confirms
+    # that lib_config is still what it reads.
+    php_lib_config_capabilities = {
         Capabilities.APM_TRACING_CUSTOM_TAGS,
         Capabilities.APM_TRACING_ENABLED,
         Capabilities.APM_TRACING_HTTP_HEADER_TAGS,
@@ -237,8 +220,16 @@ def test_resolve_sdk_configuration_contract():
         Capabilities.APM_TRACING_MULTICONFIG,
         Capabilities.SDK_CONFIGURATION,
     }
-    assert rc.resolve_sdk_configuration_contract(mixed_capabilities, library_name="nodejs") is True
-    assert rc.resolve_sdk_configuration_contract(mixed_capabilities, library_name="php") is False
+    assert rc.resolve_sdk_configuration_contract(php_lib_config_capabilities, library_name="php") is False
+
+    # dd-trace-js 6.19.0+: all nine restored per-setting bits are compatibility metadata, but
+    # sdk_config remains the only application path.
+    nodejs_6_19_apm_capabilities = php_lib_config_capabilities | {
+        Capabilities.APM_TRACING_ENABLE_CODE_ORIGIN,
+        Capabilities.APM_TRACING_ENABLE_DYNAMIC_INSTRUMENTATION,
+        Capabilities.APM_TRACING_ENABLE_LIVE_DEBUGGING,
+    }
+    assert rc.resolve_sdk_configuration_contract(nodejs_6_19_apm_capabilities, library_name="nodejs") is True
 
     # dd-trace-java: no SDK_CONFIGURATION at all
     assert (

From b64c305295c13f0f7be5b79823a2a545e25cb922 Mon Sep 17 00:00:00 2001
From: Mikayla Toffler <mikayla.toffler@datadoghq.com>
Date: Thu, 1 Oct 2026 14:40:41 -0400
Subject: [PATCH 05/12] test(remote-config): clarify capability fixtures

---
 tests/test_the_test/test_remote_config.py | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/tests/test_the_test/test_remote_config.py b/tests/test_the_test/test_remote_config.py
index 951a825172c..397a6957a93 100644
--- a/tests/test_the_test/test_remote_config.py
+++ b/tests/test_the_test/test_remote_config.py
@@ -208,15 +208,18 @@ def test_resolve_sdk_configuration_contract():
         }
     )
 
-    # dd-trace-php: bit 49 is ASM_RAW_RESPONSE_BODY there, and the per-setting fingerprint confirms
-    # that lib_config is still what it reads.
-    php_lib_config_capabilities = {
+    core_lib_config_capabilities = {
         Capabilities.APM_TRACING_CUSTOM_TAGS,
         Capabilities.APM_TRACING_ENABLED,
         Capabilities.APM_TRACING_HTTP_HEADER_TAGS,
         Capabilities.APM_TRACING_LOGS_INJECTION,
         Capabilities.APM_TRACING_SAMPLE_RATE,
         Capabilities.APM_TRACING_SAMPLE_RULES,
+    }
+
+    # dd-trace-php: bit 49 is ASM_RAW_RESPONSE_BODY there, and the per-setting fingerprint confirms
+    # that lib_config is still what it reads.
+    php_lib_config_capabilities = core_lib_config_capabilities | {
         Capabilities.APM_TRACING_MULTICONFIG,
         Capabilities.SDK_CONFIGURATION,
     }
@@ -224,12 +227,16 @@ def test_resolve_sdk_configuration_contract():
 
     # dd-trace-js 6.19.0+: all nine restored per-setting bits are compatibility metadata, but
     # sdk_config remains the only application path.
-    nodejs_6_19_apm_capabilities = php_lib_config_capabilities | {
+    nodejs_sdk_config_with_legacy_capabilities = core_lib_config_capabilities | {
+        Capabilities.APM_TRACING_MULTICONFIG,
         Capabilities.APM_TRACING_ENABLE_CODE_ORIGIN,
         Capabilities.APM_TRACING_ENABLE_DYNAMIC_INSTRUMENTATION,
         Capabilities.APM_TRACING_ENABLE_LIVE_DEBUGGING,
+        Capabilities.SDK_CONFIGURATION,
     }
-    assert rc.resolve_sdk_configuration_contract(nodejs_6_19_apm_capabilities, library_name="nodejs") is True
+    assert (
+        rc.resolve_sdk_configuration_contract(nodejs_sdk_config_with_legacy_capabilities, library_name="nodejs") is True
+    )
 
     # dd-trace-java: no SDK_CONFIGURATION at all
     assert (

From 9fb3bd0e7dd67c75a2de57aa3e13194a4bc1d870 Mon Sep 17 00:00:00 2001
From: Mikayla Toffler <mikayla.toffler@datadoghq.com>
Date: Thu, 1 Oct 2026 14:44:57 -0400
Subject: [PATCH 06/12] fix(nodejs): apply restored capabilities to main

---
 tests/parametric/capabilities.yml | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/tests/parametric/capabilities.yml b/tests/parametric/capabilities.yml
index c2e00568a52..26b98ded803 100644
--- a/tests/parametric/capabilities.yml
+++ b/tests/parametric/capabilities.yml
@@ -71,9 +71,8 @@ capabilities:
 
     # SDK_CONFIGURATION supersedes the per-setting APM_TRACING capabilities in the 5.x
     # line from 5.128.0 and in the 6.x line from 6.17.0. Node.js 6.19.0 restores the
-    # legacy bits as compatibility metadata while continuing to consume sdk_config. Keep the
-    # restored-bit range below 7.0.0: the main branch reports 7.0.0-pre before this change lands.
-    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0 <7.0.0-0':
+    # legacy bits as compatibility metadata while continuing to consume sdk_config.
+    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
       - APM_TRACING_CUSTOM_TAGS
       - APM_TRACING_ENABLED
       - APM_TRACING_HTTP_HEADER_TAGS
@@ -90,11 +89,11 @@ capabilities:
     '>=5.83.0':
       - APM_TRACING_MULTICONFIG
 
-    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0 <7.0.0-0':
+    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
       - APM_TRACING_ENABLE_CODE_ORIGIN
       - APM_TRACING_ENABLE_DYNAMIC_INSTRUMENTATION
 
-    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0 <7.0.0-0':
+    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
       - APM_TRACING_ENABLE_LIVE_DEBUGGING
 
   python:

From 5ac37c0691804da3aad399ae0bf783c4e41bea4f Mon Sep 17 00:00:00 2001
From: Mikayla Toffler <mikayla.toffler@datadoghq.com>
Date: Thu, 1 Oct 2026 15:06:10 -0400
Subject: [PATCH 07/12] [nodejs]: fix(remote-config): preserve main capability
 compatibility

---
 tests/parametric/capabilities.yml | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tests/parametric/capabilities.yml b/tests/parametric/capabilities.yml
index 26b98ded803..b096845ff28 100644
--- a/tests/parametric/capabilities.yml
+++ b/tests/parametric/capabilities.yml
@@ -71,8 +71,9 @@ capabilities:
 
     # SDK_CONFIGURATION supersedes the per-setting APM_TRACING capabilities in the 5.x
     # line from 5.128.0 and in the 6.x line from 6.17.0. Node.js 6.19.0 restores the
-    # legacy bits as compatibility metadata while continuing to consume sdk_config.
-    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
+    # legacy bits as compatibility metadata while continuing to consume sdk_config. Keep the
+    # restored-bit range below 7.0.0 so this can land before the change reaches Node.js main.
+    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0 <7.0.0-0':
       - APM_TRACING_CUSTOM_TAGS
       - APM_TRACING_ENABLED
       - APM_TRACING_HTTP_HEADER_TAGS
@@ -89,11 +90,11 @@ capabilities:
     '>=5.83.0':
       - APM_TRACING_MULTICONFIG
 
-    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
+    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0 <7.0.0-0':
       - APM_TRACING_ENABLE_CODE_ORIGIN
       - APM_TRACING_ENABLE_DYNAMIC_INSTRUMENTATION
 
-    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
+    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0 <7.0.0-0':
       - APM_TRACING_ENABLE_LIVE_DEBUGGING
 
   python:

From 7435ab743d196827b9b51cd3fa70e8d5055ec7d8 Mon Sep 17 00:00:00 2001
From: Mikayla Toffler <mikayla.toffler@datadoghq.com>
Date: Fri, 2 Oct 2026 11:28:13 -0400
Subject: [PATCH 08/12] fix(remote-config): make SDK capability authoritative

---
 tests/parametric/capabilities.yml             |  9 ++-
 .../parametric/test_dynamic_configuration.py  | 16 ++---
 tests/test_the_test/test_remote_config.py     | 65 +++++++++----------
 utils/_remote_config.py                       | 44 ++-----------
 4 files changed, 46 insertions(+), 88 deletions(-)

diff --git a/tests/parametric/capabilities.yml b/tests/parametric/capabilities.yml
index b096845ff28..26b98ded803 100644
--- a/tests/parametric/capabilities.yml
+++ b/tests/parametric/capabilities.yml
@@ -71,9 +71,8 @@ capabilities:
 
     # SDK_CONFIGURATION supersedes the per-setting APM_TRACING capabilities in the 5.x
     # line from 5.128.0 and in the 6.x line from 6.17.0. Node.js 6.19.0 restores the
-    # legacy bits as compatibility metadata while continuing to consume sdk_config. Keep the
-    # restored-bit range below 7.0.0 so this can land before the change reaches Node.js main.
-    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0 <7.0.0-0':
+    # legacy bits as compatibility metadata while continuing to consume sdk_config.
+    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
       - APM_TRACING_CUSTOM_TAGS
       - APM_TRACING_ENABLED
       - APM_TRACING_HTTP_HEADER_TAGS
@@ -90,11 +89,11 @@ capabilities:
     '>=5.83.0':
       - APM_TRACING_MULTICONFIG
 
-    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0 <7.0.0-0':
+    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
       - APM_TRACING_ENABLE_CODE_ORIGIN
       - APM_TRACING_ENABLE_DYNAMIC_INSTRUMENTATION
 
-    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0 <7.0.0-0':
+    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
       - APM_TRACING_ENABLE_LIVE_DEBUGGING
 
   python:
diff --git a/tests/parametric/test_dynamic_configuration.py b/tests/parametric/test_dynamic_configuration.py
index d25ee305009..215d81a21e2 100644
--- a/tests/parametric/test_dynamic_configuration.py
+++ b/tests/parametric/test_dynamic_configuration.py
@@ -193,10 +193,10 @@ def uses_sdk_configuration(test_agent: TestAgentAPI) -> bool:
 def assert_rc_capability(test_agent: TestAgentAPI, capability: Capabilities, wait_loops: int = 100) -> None:
     """Assert that the tracer advertises the capability to remotely configure one setting.
 
-    A tracer that has moved to the unified SDK_CONFIGURATION contract can use that bit for every
-    remotely configurable setting, so it stands in for any missing per-setting one. The
-    SDK_CONFIGURATION bit on its own does not, since libdatadog gives that bit a different meaning;
-    only a tracer whose capability combination identifies the unified contract qualifies.
+    A tracer that has moved to the unified SDK_CONFIGURATION contract advertises that single bit
+    for every remotely configurable setting instead of the per-setting ones, so it stands in for
+    any of them. The SDK_CONFIGURATION bit on its own does not, since libdatadog gives that bit a
+    different meaning; only a tracer that has really dropped the per-setting bits qualifies.
     """
     seen_capabilities = test_agent.wait_for_rc_capabilities(wait_loops)
     if capability in seen_capabilities:
@@ -581,10 +581,10 @@ def test_tracing_client_tracing_disable_one_way(
 class Test_DynamicConfigSdkConfiguration:
     """Coverage for the generic sdk_config RC delivery path.
 
-    sdk_config carries settings as generic env-var-keyed entries, applied via the unified
-    SDK_CONFIGURATION contract instead of custom per-setting parsing. These tests confirm a tracer
-    on that contract consumes sdk_config with no regression in behavior compared to the equivalent
-    lib_config delivery, starting with DD_TRACE_ENABLED.
+    sdk_config carries settings as generic env-var-keyed entries, applied via the single
+    SDK_CONFIGURATION capability instead of custom per-setting parsing. These tests confirm a
+    tracer that declares SDK_CONFIGURATION consumes sdk_config with no regression in behavior
+    compared to the equivalent lib_config delivery, starting with DD_TRACE_ENABLED.
 
     test_sdk_config_tracing_enabled_matches_lib_config asserts real behavior (tracing actually
     stops) for DD_TRACE_ENABLED. test_sdk_config_field_is_applied then layers a shallower
diff --git a/tests/test_the_test/test_remote_config.py b/tests/test_the_test/test_remote_config.py
index 397a6957a93..a5db4ca5e4f 100644
--- a/tests/test_the_test/test_remote_config.py
+++ b/tests/test_the_test/test_remote_config.py
@@ -192,14 +192,8 @@ def test_build_apm_tracing_command_legacy_by_default():
 
 
 @scenarios.test_the_test
-def test_resolve_sdk_configuration_contract():
-    """The SDK_CONFIGURATION bit alone does not mean the library reads sdk_config.
-
-    Bit 49 is SDK_CONFIGURATION in the remote config source of truth, but libdatadog gives the
-    same bit to ASM_RAW_RESPONSE_BODY. Capability interpretation therefore also needs to account
-    for the tracer implementation when legacy bits and SDK_CONFIGURATION appear together.
-    """
-    # dd-trace-js 6.17.0 and 6.18.0: the per-setting capabilities are dropped
+def test_sdk_configuration_alone_selects_sdk_config():
+    """SDK_CONFIGURATION without per-setting APM_TRACING capabilities selects sdk_config."""
     assert rc.resolve_sdk_configuration_contract(
         {
             Capabilities.ASM_ACTIVATION,
@@ -208,49 +202,50 @@ def test_resolve_sdk_configuration_contract():
         }
     )
 
-    core_lib_config_capabilities = {
+
+@scenarios.test_the_test
+def test_sdk_configuration_with_apm_tracing_capabilities_selects_sdk_config():
+    """SDK_CONFIGURATION alongside per-setting APM_TRACING capabilities selects sdk_config."""
+    capabilities = {
         Capabilities.APM_TRACING_CUSTOM_TAGS,
         Capabilities.APM_TRACING_ENABLED,
         Capabilities.APM_TRACING_HTTP_HEADER_TAGS,
         Capabilities.APM_TRACING_LOGS_INJECTION,
         Capabilities.APM_TRACING_SAMPLE_RATE,
         Capabilities.APM_TRACING_SAMPLE_RULES,
-    }
-
-    # dd-trace-php: bit 49 is ASM_RAW_RESPONSE_BODY there, and the per-setting fingerprint confirms
-    # that lib_config is still what it reads.
-    php_lib_config_capabilities = core_lib_config_capabilities | {
-        Capabilities.APM_TRACING_MULTICONFIG,
-        Capabilities.SDK_CONFIGURATION,
-    }
-    assert rc.resolve_sdk_configuration_contract(php_lib_config_capabilities, library_name="php") is False
-
-    # dd-trace-js 6.19.0+: all nine restored per-setting bits are compatibility metadata, but
-    # sdk_config remains the only application path.
-    nodejs_sdk_config_with_legacy_capabilities = core_lib_config_capabilities | {
         Capabilities.APM_TRACING_MULTICONFIG,
         Capabilities.APM_TRACING_ENABLE_CODE_ORIGIN,
         Capabilities.APM_TRACING_ENABLE_DYNAMIC_INSTRUMENTATION,
         Capabilities.APM_TRACING_ENABLE_LIVE_DEBUGGING,
         Capabilities.SDK_CONFIGURATION,
     }
-    assert (
-        rc.resolve_sdk_configuration_contract(nodejs_sdk_config_with_legacy_capabilities, library_name="nodejs") is True
-    )
 
-    # dd-trace-java: no SDK_CONFIGURATION at all
-    assert (
-        rc.resolve_sdk_configuration_contract({Capabilities.APM_TRACING_SAMPLE_RATE, Capabilities.APM_TRACING_ENABLED})
-        is False
-    )
+    assert rc.resolve_sdk_configuration_contract(capabilities) is True
+
+
+@scenarios.test_the_test
+def test_apm_tracing_capabilities_without_sdk_configuration_select_lib_config():
+    """Per-setting APM_TRACING capabilities without SDK_CONFIGURATION select lib_config."""
+    capabilities = {
+        Capabilities.APM_TRACING_CUSTOM_TAGS,
+        Capabilities.APM_TRACING_ENABLED,
+        Capabilities.APM_TRACING_HTTP_HEADER_TAGS,
+        Capabilities.APM_TRACING_LOGS_INJECTION,
+        Capabilities.APM_TRACING_SAMPLE_RATE,
+        Capabilities.APM_TRACING_SAMPLE_RULES,
+        Capabilities.APM_TRACING_MULTICONFIG,
+    }
+
+    assert rc.resolve_sdk_configuration_contract(capabilities) is False
+
+
+@scenarios.test_the_test
+def test_resolve_sdk_configuration_contract_waits_for_apm_capabilities():
+    """Capability registration is inconclusive until an APM_TRACING capability is present."""
 
-    # Only ASM capabilities registered so far: nothing to conclude, ask again later
     assert rc.resolve_sdk_configuration_contract({Capabilities.ASM_ACTIVATION}) is None
     assert rc.resolve_sdk_configuration_contract(set()) is None
 
-    # A libdatadog library mid-startup: bit 49 is registered with the other AppSec capabilities,
-    # before any APM_TRACING one. The absence of the per-setting bits is not evidence of the
-    # unified contract yet, so this must stay inconclusive rather than be cached as sdk_config.
     assert (
         rc.resolve_sdk_configuration_contract(
             {
@@ -262,7 +257,6 @@ def test_resolve_sdk_configuration_contract():
         is None
     )
 
-    # APM_TRACING registered but no SDK_CONFIGURATION: conclusively lib_config
     assert (
         rc.resolve_sdk_configuration_contract(
             {Capabilities.APM_TRACING_MULTICONFIG, Capabilities.APM_TRACING_ENABLE_CODE_ORIGIN}
@@ -279,5 +273,4 @@ def test_apm_tracing_capabilities_exclude_sdk_configuration():
     `resolve_sdk_configuration_contract`.
     """
     assert Capabilities.SDK_CONFIGURATION not in rc.APM_TRACING_CAPABILITIES
-    assert rc.LIB_CONFIG_CAPABILITY_FINGERPRINT <= rc.APM_TRACING_CAPABILITIES
     assert Capabilities.APM_TRACING_MULTICONFIG in rc.APM_TRACING_CAPABILITIES
diff --git a/utils/_remote_config.py b/utils/_remote_config.py
index 087be24c9c5..19edf9fd400 100644
--- a/utils/_remote_config.py
+++ b/utils/_remote_config.py
@@ -645,54 +645,20 @@ def to_sdk_config_payload(config: dict[str, Any]) -> dict[str, Any]:
     capability for capability in Capabilities if capability.name.startswith("APM_TRACING_")
 )
 
-# The per-setting capability fingerprint observed on libraries that consume `lib_config`. This is
-# deliberately not an exhaustive set of legacy APM_TRACING capabilities: optional feature bits do
-# not reliably identify the payload contract. Node.js 6.19.0+ re-advertises this fingerprint for
-# backend/frontend compatibility while continuing to consume `sdk_config`.
-LIB_CONFIG_CAPABILITY_FINGERPRINT = frozenset(
-    {
-        Capabilities.APM_TRACING_CUSTOM_TAGS,
-        Capabilities.APM_TRACING_ENABLED,
-        Capabilities.APM_TRACING_HTTP_HEADER_TAGS,
-        Capabilities.APM_TRACING_LOGS_INJECTION,
-        Capabilities.APM_TRACING_SAMPLE_RATE,
-        Capabilities.APM_TRACING_SAMPLE_RULES,
-    }
-)
-
 
-def resolve_sdk_configuration_contract(
-    capabilities: set[Capabilities], *, library_name: str | None = None
-) -> bool | None:
+def resolve_sdk_configuration_contract(capabilities: set[Capabilities]) -> bool | None:
     """Decide which APM_TRACING payload shape a set of advertised capabilities asks for.
 
     Returns True for `sdk_config`, False for `lib_config`, and None when the capabilities seen so
     far cannot tell, so the caller should look again later.
 
-    The SDK_CONFIGURATION bit alone is not enough to decide. Bit 49 is SDK_CONFIGURATION in the
-    remote config source of truth (dd-source `remote-config/shared/libs/rc/capabilities.go`), but
-    libdatadog hands the same bit to `ASM_RAW_RESPONSE_BODY`, so a libdatadog-based library such as
-    dd-trace-php advertises it while still reading `lib_config`.
-
-    For Node.js, SDK_CONFIGURATION is authoritative even when the legacy per-setting bits are also
-    present. Node.js 6.19.0 restored those bits for backend/frontend compatibility without restoring
-    the legacy `lib_config` application path.
-
-    For other tracers, the per-setting fingerprint distinguishes the two contracts. Its absence
-    only counts once the library has actually registered its APM_TRACING remote config, though:
-    capabilities are added as products start, and AppSec ones come first, so an early poll from a
-    libdatadog library shows bit 49 with no APM_TRACING bit yet and would otherwise be mistaken for
-    the unified contract.
+    SDK_CONFIGURATION is authoritative once the library has registered at least one APM_TRACING
+    capability. Waiting for an APM capability prevents an unrelated product that registers first
+    from deciding which APM_TRACING payload shape to use.
     """
     if not capabilities & APM_TRACING_CAPABILITIES:
         return None
 
-    if library_name == "nodejs" and Capabilities.SDK_CONFIGURATION in capabilities:
-        return True
-
-    if capabilities & LIB_CONFIG_CAPABILITY_FINGERPRINT:
-        return False
-
     return Capabilities.SDK_CONFIGURATION in capabilities
 
 
@@ -722,7 +688,7 @@ def resolve_sdk_configuration_support(get_capabilities: Callable[[], set[Capabil
         logger.error(f"Could not read the RC capabilities ({e}), assuming no SDK_CONFIGURATION support")
         return False
 
-    supported = resolve_sdk_configuration_contract(capabilities, library_name=context.library.name)
+    supported = resolve_sdk_configuration_contract(capabilities)
     if supported is None:
         logger.info("No APM_TRACING capability advertised yet, sending lib_config for now")
         return False

From 2de673903bdc23b2a3431fa119fbfa0228865c8e Mon Sep 17 00:00:00 2001
From: Mikayla Toffler <mikayla.toffler@datadoghq.com>
Date: Fri, 2 Oct 2026 11:30:23 -0400
Subject: [PATCH 09/12] docs(nodejs): clarify remote config capability timeline

---
 tests/parametric/capabilities.yml | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tests/parametric/capabilities.yml b/tests/parametric/capabilities.yml
index 26b98ded803..ee0022b214a 100644
--- a/tests/parametric/capabilities.yml
+++ b/tests/parametric/capabilities.yml
@@ -69,9 +69,9 @@ capabilities:
       - ASM_ACTIVATION
       - ASM_AUTO_USER_INSTRUM_MODE
 
-    # SDK_CONFIGURATION supersedes the per-setting APM_TRACING capabilities in the 5.x
-    # line from 5.128.0 and in the 6.x line from 6.17.0. Node.js 6.19.0 restores the
-    # legacy bits as compatibility metadata while continuing to consume sdk_config.
+    # Node.js consumes sdk_config starting in 5.128.0 on the 5.x release line and in
+    # 6.17.0 on the 6.x release line. Starting in 6.19.0, it also advertises the
+    # per-setting APM_TRACING capabilities for backend and UI compatibility.
     '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
       - APM_TRACING_CUSTOM_TAGS
       - APM_TRACING_ENABLED

From a7b20fddb771d2630273bffdeccf925d8edd6ba1 Mon Sep 17 00:00:00 2001
From: Mikayla Toffler <mikayla.toffler@datadoghq.com>
Date: Fri, 2 Oct 2026 14:24:06 -0400
Subject: [PATCH 10/12] fix(remote-config): require Node.js 6.20 for restored
 bits

---
 tests/parametric/capabilities.yml | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tests/parametric/capabilities.yml b/tests/parametric/capabilities.yml
index ee0022b214a..98fc857a464 100644
--- a/tests/parametric/capabilities.yml
+++ b/tests/parametric/capabilities.yml
@@ -70,9 +70,9 @@ capabilities:
       - ASM_AUTO_USER_INSTRUM_MODE
 
     # Node.js consumes sdk_config starting in 5.128.0 on the 5.x release line and in
-    # 6.17.0 on the 6.x release line. Starting in 6.19.0, it also advertises the
+    # 6.17.0 on the 6.x release line. Starting in 6.20.0, it also advertises the
     # per-setting APM_TRACING capabilities for backend and UI compatibility.
-    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
+    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.20.0':
       - APM_TRACING_CUSTOM_TAGS
       - APM_TRACING_ENABLED
       - APM_TRACING_HTTP_HEADER_TAGS
@@ -89,11 +89,11 @@ capabilities:
     '>=5.83.0':
       - APM_TRACING_MULTICONFIG
 
-    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
+    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.20.0':
       - APM_TRACING_ENABLE_CODE_ORIGIN
       - APM_TRACING_ENABLE_DYNAMIC_INSTRUMENTATION
 
-    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.19.0':
+    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.20.0':
       - APM_TRACING_ENABLE_LIVE_DEBUGGING
 
   python:

From 41470383eacf79b3e13ba25d0757444d385205e4 Mon Sep 17 00:00:00 2001
From: Mikayla Toffler <mikayla.toffler@datadoghq.com>
Date: Fri, 2 Oct 2026 15:07:29 -0400
Subject: [PATCH 11/12] fix(remote-config): allow Node.js 7 prerelease
 capability drift

---
 tests/parametric/capabilities.yml | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tests/parametric/capabilities.yml b/tests/parametric/capabilities.yml
index 98fc857a464..12567bbecd4 100644
--- a/tests/parametric/capabilities.yml
+++ b/tests/parametric/capabilities.yml
@@ -72,7 +72,7 @@ capabilities:
     # Node.js consumes sdk_config starting in 5.128.0 on the 5.x release line and in
     # 6.17.0 on the 6.x release line. Starting in 6.20.0, it also advertises the
     # per-setting APM_TRACING capabilities for backend and UI compatibility.
-    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.20.0':
+    '<5.128.0 || >=6.0.0-0 <6.17.0 || >=6.20.0 <7.0.0-0 || >=7.0.0':
       - APM_TRACING_CUSTOM_TAGS
       - APM_TRACING_ENABLED
       - APM_TRACING_HTTP_HEADER_TAGS
@@ -89,11 +89,11 @@ capabilities:
     '>=5.83.0':
       - APM_TRACING_MULTICONFIG
 
-    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.20.0':
+    '>=5.83.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.20.0 <7.0.0-0 || >=7.0.0':
       - APM_TRACING_ENABLE_CODE_ORIGIN
       - APM_TRACING_ENABLE_DYNAMIC_INSTRUMENTATION
 
-    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.20.0':
+    '>=5.84.0 <5.128.0 || >=6.0.0-0 <6.17.0 || >=6.20.0 <7.0.0-0 || >=7.0.0':
       - APM_TRACING_ENABLE_LIVE_DEBUGGING
 
   python:

From 1b3e5c59b3ff686a9e1f5c1e2e0c802d7680a193 Mon Sep 17 00:00:00 2001
From: Mikayla Toffler <mikayla.toffler@datadoghq.com>
Date: Mon, 5 Oct 2026 13:50:44 -0400
Subject: [PATCH 12/12] fix(remote-config): preserve PHP bit 49 collision

---
 .../parametric/test_dynamic_configuration.py  | 13 +++---
 tests/test_the_test/test_remote_config.py     | 22 ++++++++-
 utils/_remote_config.py                       | 46 +++++++++++++++----
 3 files changed, 63 insertions(+), 18 deletions(-)

diff --git a/tests/parametric/test_dynamic_configuration.py b/tests/parametric/test_dynamic_configuration.py
index 215d81a21e2..0df04ad988b 100644
--- a/tests/parametric/test_dynamic_configuration.py
+++ b/tests/parametric/test_dynamic_configuration.py
@@ -187,22 +187,23 @@ def uses_sdk_configuration(test_agent: TestAgentAPI) -> bool:
     that does not poll remote config (tracing disabled by DD_TRACE_ENABLED, for instance) looks
     like; the shared helper turns that into the `lib_config` default.
     """
-    return remote_config.resolve_sdk_configuration_support(lambda: test_agent.wait_for_rc_capabilities(_RC_WAIT_LOOPS))
+    return remote_config.resolve_sdk_configuration_support(
+        lambda: test_agent.wait_for_rc_capabilities(_RC_WAIT_LOOPS), library_name=context.library.name
+    )
 
 
 def assert_rc_capability(test_agent: TestAgentAPI, capability: Capabilities, wait_loops: int = 100) -> None:
     """Assert that the tracer advertises the capability to remotely configure one setting.
 
-    A tracer that has moved to the unified SDK_CONFIGURATION contract advertises that single bit
-    for every remotely configurable setting instead of the per-setting ones, so it stands in for
-    any of them. The SDK_CONFIGURATION bit on its own does not, since libdatadog gives that bit a
-    different meaning; only a tracer that has really dropped the per-setting bits qualifies.
+    A tracer that has moved to the unified SDK_CONFIGURATION contract may advertise that bit in
+    place of a per-setting capability. Since libdatadog gives the same bit a different meaning,
+    the shared resolver also uses the library identity when legacy capabilities remain present.
     """
     seen_capabilities = test_agent.wait_for_rc_capabilities(wait_loops)
     if capability in seen_capabilities:
         return
 
-    assert remote_config.resolve_sdk_configuration_contract(seen_capabilities), (
+    assert remote_config.resolve_sdk_configuration_contract(seen_capabilities, library_name=context.library.name), (
         f"RemoteConfig capability missing: neither {capability.name} nor the SDK_CONFIGURATION "
         f"contract that replaces it; seen: {seen_capabilities}"
     )
diff --git a/tests/test_the_test/test_remote_config.py b/tests/test_the_test/test_remote_config.py
index a5db4ca5e4f..878e2a70d79 100644
--- a/tests/test_the_test/test_remote_config.py
+++ b/tests/test_the_test/test_remote_config.py
@@ -205,7 +205,7 @@ def test_sdk_configuration_alone_selects_sdk_config():
 
 @scenarios.test_the_test
 def test_sdk_configuration_with_apm_tracing_capabilities_selects_sdk_config():
-    """SDK_CONFIGURATION alongside per-setting APM_TRACING capabilities selects sdk_config."""
+    """Node.js uses sdk_config while continuing to advertise per-setting capabilities."""
     capabilities = {
         Capabilities.APM_TRACING_CUSTOM_TAGS,
         Capabilities.APM_TRACING_ENABLED,
@@ -220,7 +220,24 @@ def test_sdk_configuration_with_apm_tracing_capabilities_selects_sdk_config():
         Capabilities.SDK_CONFIGURATION,
     }
 
-    assert rc.resolve_sdk_configuration_contract(capabilities) is True
+    assert rc.resolve_sdk_configuration_contract(capabilities, library_name="nodejs") is True
+
+
+@scenarios.test_the_test
+def test_php_bit_49_collision_with_apm_tracing_capabilities_selects_lib_config():
+    """PHP uses bit 49 for ASM_RAW_RESPONSE_BODY and continues to consume lib_config."""
+    capabilities = {
+        Capabilities.APM_TRACING_CUSTOM_TAGS,
+        Capabilities.APM_TRACING_ENABLED,
+        Capabilities.APM_TRACING_HTTP_HEADER_TAGS,
+        Capabilities.APM_TRACING_LOGS_INJECTION,
+        Capabilities.APM_TRACING_SAMPLE_RATE,
+        Capabilities.APM_TRACING_SAMPLE_RULES,
+        Capabilities.APM_TRACING_MULTICONFIG,
+        Capabilities.SDK_CONFIGURATION,
+    }
+
+    assert rc.resolve_sdk_configuration_contract(capabilities, library_name="php") is False
 
 
 @scenarios.test_the_test
@@ -273,4 +290,5 @@ def test_apm_tracing_capabilities_exclude_sdk_configuration():
     `resolve_sdk_configuration_contract`.
     """
     assert Capabilities.SDK_CONFIGURATION not in rc.APM_TRACING_CAPABILITIES
+    assert rc.LEGACY_APM_TRACING_CAPABILITIES <= rc.APM_TRACING_CAPABILITIES
     assert Capabilities.APM_TRACING_MULTICONFIG in rc.APM_TRACING_CAPABILITIES
diff --git a/utils/_remote_config.py b/utils/_remote_config.py
index 19edf9fd400..7dc11cefca0 100644
--- a/utils/_remote_config.py
+++ b/utils/_remote_config.py
@@ -645,21 +645,44 @@ def to_sdk_config_payload(config: dict[str, Any]) -> dict[str, Any]:
     capability for capability in Capabilities if capability.name.startswith("APM_TRACING_")
 )
 
+# The per-setting capabilities replaced by the unified SDK_CONFIGURATION contract. Their presence
+# alongside bit 49 is ambiguous: Node.js intentionally advertises both families, while libdatadog
+# uses bit 49 for ASM_RAW_RESPONSE_BODY and still consumes the legacy lib_config payload.
+LEGACY_APM_TRACING_CAPABILITIES = frozenset(
+    {
+        Capabilities.APM_TRACING_CUSTOM_TAGS,
+        Capabilities.APM_TRACING_ENABLED,
+        Capabilities.APM_TRACING_HTTP_HEADER_TAGS,
+        Capabilities.APM_TRACING_LOGS_INJECTION,
+        Capabilities.APM_TRACING_SAMPLE_RATE,
+        Capabilities.APM_TRACING_SAMPLE_RULES,
+    }
+)
+
 
-def resolve_sdk_configuration_contract(capabilities: set[Capabilities]) -> bool | None:
+def resolve_sdk_configuration_contract(
+    capabilities: set[Capabilities], *, library_name: str | None = None
+) -> bool | None:
     """Decide which APM_TRACING payload shape a set of advertised capabilities asks for.
 
     Returns True for `sdk_config`, False for `lib_config`, and None when the capabilities seen so
     far cannot tell, so the caller should look again later.
 
-    SDK_CONFIGURATION is authoritative once the library has registered at least one APM_TRACING
-    capability. Waiting for an APM capability prevents an unrelated product that registers first
-    from deciding which APM_TRACING payload shape to use.
+    Waiting for an APM capability prevents an unrelated product that registers first from deciding
+    which APM_TRACING payload shape to use. When bit 49 appears with legacy per-setting bits, only
+    Node.js treats it as SDK_CONFIGURATION; libdatadog libraries use the same bit for
+    ASM_RAW_RESPONSE_BODY and still consume lib_config.
     """
     if not capabilities & APM_TRACING_CAPABILITIES:
         return None
 
-    return Capabilities.SDK_CONFIGURATION in capabilities
+    if Capabilities.SDK_CONFIGURATION not in capabilities:
+        return False
+
+    if capabilities & LEGACY_APM_TRACING_CAPABILITIES:
+        return library_name == "nodejs"
+
+    return True
 
 
 # Memoized once the capabilities are conclusive, both to skip re-scanning the whole /v0.7/config
@@ -668,11 +691,14 @@ def resolve_sdk_configuration_contract(capabilities: set[Capabilities]) -> bool
 _sdk_configuration_support: dict[str, bool] = {}
 
 
-def resolve_sdk_configuration_support(get_capabilities: Callable[[], set[Capabilities]]) -> bool:
+def resolve_sdk_configuration_support(
+    get_capabilities: Callable[[], set[Capabilities]], *, library_name: str | None = None
+) -> bool:
     """Whether the library reads its APM_TRACING settings from `sdk_config` instead of `lib_config`.
 
-    `get_capabilities` returns the capabilities the library currently advertises. How to obtain
-    them, and how long to wait for them, differs between the end-to-end interface and the
+    `get_capabilities` returns the capabilities the library currently advertises. `library_name`
+    resolves bit 49 when it appears alongside legacy per-setting capabilities. How to obtain the
+    capabilities, and how long to wait for them, differs between the end-to-end interface and the
     parametric test agent, so that part stays with the caller; everything after it is shared.
 
     Falls back to `lib_config` whenever the answer is not yet knowable, which is the safe
@@ -688,7 +714,7 @@ def resolve_sdk_configuration_support(get_capabilities: Callable[[], set[Capabil
         logger.error(f"Could not read the RC capabilities ({e}), assuming no SDK_CONFIGURATION support")
         return False
 
-    supported = resolve_sdk_configuration_contract(capabilities)
+    supported = resolve_sdk_configuration_contract(capabilities, library_name=library_name)
     if supported is None:
         logger.info("No APM_TRACING capability advertised yet, sending lib_config for now")
         return False
@@ -709,7 +735,7 @@ def library_supports_sdk_configuration() -> bool:
         logger.warning("No remote config request seen, assuming the library does not support SDK_CONFIGURATION")
         return False
 
-    return resolve_sdk_configuration_support(library.get_rc_capabilities)
+    return resolve_sdk_configuration_support(library.get_rc_capabilities, library_name=context.library.name)
 
 
 def build_apm_tracing_command(