diff --git a/ci/init.js b/ci/init.js
index 748194919e8..202a2080dba 100644
--- a/ci/init.js
+++ b/ci/init.js
@@ -5,6 +5,7 @@ const tracer = require('../packages/dd-trace')
 const { isTrue, isFalse } = require('../packages/dd-trace/src/util')
 const log = require('../packages/dd-trace/src/log')
 const { getEnvironmentVariable } = require('../packages/dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../packages/dd-trace/src/config-env-sources')
 
 const PACKAGE_MANAGERS = ['npm', 'yarn', 'pnpm']
 const DEFAULT_FLUSH_INTERVAL = 5000
@@ -43,8 +44,8 @@ const baseOptions = {
   flushInterval: isJestWorker ? JEST_FLUSH_INTERVAL : DEFAULT_FLUSH_INTERVAL
 }
 
-let shouldInit = !isFalse(getEnvironmentVariable('DD_CIVISIBILITY_ENABLED'))
-const isAgentlessEnabled = isTrue(getEnvironmentVariable('DD_CIVISIBILITY_AGENTLESS_ENABLED'))
+let shouldInit = !isFalse(getResolvedEnv('DD_CIVISIBILITY_ENABLED'))
+const isAgentlessEnabled = isTrue(getResolvedEnv('DD_CIVISIBILITY_AGENTLESS_ENABLED'))
 
 if (!isTestWorker && isPackageManager()) {
   log.debug('dd-trace is not initialized in a package manager.')
@@ -58,7 +59,7 @@ if (isTestWorker) {
   }
 } else {
   if (isAgentlessEnabled) {
-    if (getEnvironmentVariable('DD_API_KEY')) {
+    if (getResolvedEnv('DD_API_KEY')) {
       baseOptions.experimental = {
         exporter: 'datadog'
       }
diff --git a/packages/datadog-instrumentations/src/helpers/register.js b/packages/datadog-instrumentations/src/helpers/register.js
index 6e5f0f3985a..0d7b490233e 100644
--- a/packages/datadog-instrumentations/src/helpers/register.js
+++ b/packages/datadog-instrumentations/src/helpers/register.js
@@ -9,14 +9,10 @@ const log = require('../../../dd-trace/src/log')
 const checkRequireCache = require('./check-require-cache')
 const telemetry = require('../../../dd-trace/src/guardrails/telemetry')
 const { isInServerlessEnvironment } = require('../../../dd-trace/src/serverless')
-const { getEnvironmentVariables } = require('../../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../../dd-trace/src/config-env-sources')
 
-const envs = getEnvironmentVariables()
-
-const {
-  DD_TRACE_DISABLED_INSTRUMENTATIONS = '',
-  DD_TRACE_DEBUG = ''
-} = envs
+const DD_TRACE_DISABLED_INSTRUMENTATIONS = getResolvedEnv('DD_TRACE_DISABLED_INSTRUMENTATIONS') || ''
+const DD_TRACE_DEBUG = getResolvedEnv('DD_TRACE_DEBUG') || ''
 
 const hooks = require('./hooks')
 const instrumentations = require('./instrumentations')
diff --git a/packages/datadog-instrumentations/src/otel-sdk-trace.js b/packages/datadog-instrumentations/src/otel-sdk-trace.js
index 90c9f30f475..3f50b94e263 100644
--- a/packages/datadog-instrumentations/src/otel-sdk-trace.js
+++ b/packages/datadog-instrumentations/src/otel-sdk-trace.js
@@ -3,11 +3,11 @@
 const { addHook } = require('./helpers/instrument')
 const shimmer = require('../../datadog-shimmer')
 const tracer = require('../../dd-trace')
-const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../dd-trace/src/config-env-sources')
 
-const otelSdkEnabled = getEnvironmentVariable('DD_TRACE_OTEL_ENABLED') ||
-getEnvironmentVariable('OTEL_SDK_DISABLED')
-  ? !getEnvironmentVariable('OTEL_SDK_DISABLED')
+const otelSdkEnabled = getResolvedEnv('DD_TRACE_OTEL_ENABLED') ||
+getResolvedEnv('OTEL_SDK_DISABLED')
+  ? !getResolvedEnv('OTEL_SDK_DISABLED')
   : undefined
 
 if (otelSdkEnabled) {
diff --git a/packages/datadog-plugin-aws-sdk/src/base.js b/packages/datadog-plugin-aws-sdk/src/base.js
index 6ff6d6f4bec..a5ea309b6ae 100644
--- a/packages/datadog-plugin-aws-sdk/src/base.js
+++ b/packages/datadog-plugin-aws-sdk/src/base.js
@@ -6,6 +6,7 @@ const { storage } = require('../../datadog-core')
 const { isTrue } = require('../../dd-trace/src/util')
 const { tagsFromRequest, tagsFromResponse } = require('../../dd-trace/src/payload-tagging')
 const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../dd-trace/src/config-env-sources')
 
 class BaseAwsSdkPlugin extends ClientPlugin {
   static id = 'aws'
@@ -190,7 +191,7 @@ class BaseAwsSdkPlugin extends ClientPlugin {
 
   isEnabled (request) {
     const serviceId = this.serviceIdentifier.toUpperCase()
-    const envVarValue = getEnvironmentVariable(`DD_TRACE_AWS_SDK_${serviceId}_ENABLED`)
+    const envVarValue = getEnvironmentVariable(`DD_TRACE_AWS_SDK_${serviceId}_ENABLED`) // I'm not sure about this one
     return envVarValue ? isTrue(envVarValue) : true
   }
 
@@ -273,9 +274,10 @@ function normalizeConfig (config, serviceIdentifier) {
   const serviceId = serviceIdentifier.toUpperCase()
   const batchPropagationEnabled = isTrue(
     specificConfig.batchPropagationEnabled ??
+    // Or this one
     getEnvironmentVariable(`DD_TRACE_AWS_SDK_${serviceId}_BATCH_PROPAGATION_ENABLED`) ??
     config.batchPropagationEnabled ??
-    getEnvironmentVariable('DD_TRACE_AWS_SDK_BATCH_PROPAGATION_ENABLED')
+    getResolvedEnv('DD_TRACE_AWS_SDK_BATCH_PROPAGATION_ENABLED')
   )
 
   // Merge the specific config back into the main config
diff --git a/packages/datadog-plugin-azure-event-hubs/src/producer.js b/packages/datadog-plugin-azure-event-hubs/src/producer.js
index 44e38aba99d..937c5c34c1e 100644
--- a/packages/datadog-plugin-azure-event-hubs/src/producer.js
+++ b/packages/datadog-plugin-azure-event-hubs/src/producer.js
@@ -1,6 +1,6 @@
 'use strict'
 
-const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../dd-trace/src/config-env-sources')
 const ProducerPlugin = require('../../dd-trace/src/plugins/producer')
 
 class AzureEventHubsProducerPlugin extends ProducerPlugin {
@@ -75,7 +75,7 @@ function injectTraceContext (tracer, span, event) {
 }
 
 function batchLinksAreEnabled () {
-  const eh = getEnvironmentVariable('DD_TRACE_AZURE_EVENTHUBS_BATCH_LINKS_ENABLED')
+  const eh = getResolvedEnv('DD_TRACE_AZURE_EVENTHUBS_BATCH_LINKS_ENABLED')
   return eh !== 'false'
 }
 
diff --git a/packages/datadog-plugin-azure-service-bus/src/producer.js b/packages/datadog-plugin-azure-service-bus/src/producer.js
index 8fdd67f4cc7..bfa023f7cff 100644
--- a/packages/datadog-plugin-azure-service-bus/src/producer.js
+++ b/packages/datadog-plugin-azure-service-bus/src/producer.js
@@ -1,6 +1,6 @@
 'use strict'
 
-const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../dd-trace/src/config-env-sources')
 const ProducerPlugin = require('../../dd-trace/src/plugins/producer')
 const spanContexts = new WeakMap()
 
@@ -86,7 +86,7 @@ function injectTraceContext (tracer, span, msg) {
 }
 
 function batchLinksAreEnabled () {
-  const sb = getEnvironmentVariable('DD_TRACE_AZURE_SERVICEBUS_BATCH_LINKS_ENABLED')
+  const sb = getResolvedEnv('DD_TRACE_AZURE_SERVICEBUS_BATCH_LINKS_ENABLED')
   return sb !== 'false'
 }
 
diff --git a/packages/datadog-plugin-cucumber/src/index.js b/packages/datadog-plugin-cucumber/src/index.js
index 1168c358008..63bb236c7eb 100644
--- a/packages/datadog-plugin-cucumber/src/index.js
+++ b/packages/datadog-plugin-cucumber/src/index.js
@@ -3,6 +3,7 @@
 const CiPlugin = require('../../dd-trace/src/plugins/ci_plugin')
 const { storage } = require('../../datadog-core')
 const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../dd-trace/src/config-env-sources')
 
 const {
   TEST_SKIP_REASON,
@@ -112,7 +113,7 @@ class CucumberPlugin extends CiPlugin {
       finishAllTraceSpans(this.testSessionSpan)
       this.telemetry.count(TELEMETRY_TEST_SESSION, {
         provider: this.ciProviderName,
-        autoInjected: !!getEnvironmentVariable('DD_CIVISIBILITY_AUTO_INSTRUMENTATION_PROVIDER')
+        autoInjected: !!getResolvedEnv('DD_CIVISIBILITY_AUTO_INSTRUMENTATION_PROVIDER')
       })
 
       this.libraryConfig = null
diff --git a/packages/datadog-plugin-cypress/src/cypress-plugin.js b/packages/datadog-plugin-cypress/src/cypress-plugin.js
index 842322ab24c..fbc11977b39 100644
--- a/packages/datadog-plugin-cypress/src/cypress-plugin.js
+++ b/packages/datadog-plugin-cypress/src/cypress-plugin.js
@@ -51,7 +51,7 @@ const {
 } = require('../../dd-trace/src/plugins/util/test')
 const { isMarkedAsUnskippable } = require('../../datadog-plugin-jest/src/util')
 const { ORIGIN_KEY, COMPONENT } = require('../../dd-trace/src/constants')
-const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../dd-trace/src/config-env-sources')
 const { appClosing: appClosingTelemetry } = require('../../dd-trace/src/telemetry')
 const log = require('../../dd-trace/src/log')
 
@@ -644,7 +644,7 @@ class CypressPlugin {
       this.ciVisEvent(TELEMETRY_EVENT_FINISHED, 'session')
       incrementCountMetric(TELEMETRY_TEST_SESSION, {
         provider: this.ciProviderName,
-        autoInjected: !!getEnvironmentVariable('DD_CIVISIBILITY_AUTO_INSTRUMENTATION_PROVIDER')
+        autoInjected: !!getResolvedEnv('DD_CIVISIBILITY_AUTO_INSTRUMENTATION_PROVIDER')
       })
 
       finishAllTraceSpans(this.testSessionSpan)
diff --git a/packages/datadog-plugin-dd-trace-api/src/index.js b/packages/datadog-plugin-dd-trace-api/src/index.js
index bc504550c40..6a479f6c562 100644
--- a/packages/datadog-plugin-dd-trace-api/src/index.js
+++ b/packages/datadog-plugin-dd-trace-api/src/index.js
@@ -3,13 +3,13 @@
 const Plugin = require('../../dd-trace/src/plugins/plugin')
 const telemetryMetrics = require('../../dd-trace/src/telemetry/metrics')
 const apiMetrics = telemetryMetrics.manager.namespace('tracers')
-const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../dd-trace/src/config-env-sources')
 
 // api ==> here
 const objectMap = new WeakMap()
 
 const injectionEnabledTag =
-  `injection_enabled:${getEnvironmentVariable('DD_INJECTION_ENABLED') ? 'yes' : 'no'}`
+  `injection_enabled:${getResolvedEnv('DD_INJECTION_ENABLED') ? 'yes' : 'no'}`
 
 module.exports = class DdTraceApiPlugin extends Plugin {
   static id = 'dd-trace-api'
diff --git a/packages/datadog-plugin-jest/src/index.js b/packages/datadog-plugin-jest/src/index.js
index a6ceaa143bd..c4e8fd6e8e2 100644
--- a/packages/datadog-plugin-jest/src/index.js
+++ b/packages/datadog-plugin-jest/src/index.js
@@ -3,6 +3,7 @@
 const CiPlugin = require('../../dd-trace/src/plugins/ci_plugin')
 const { storage } = require('../../datadog-core')
 const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../dd-trace/src/config-env-sources')
 
 const {
   TEST_STATUS,
@@ -161,7 +162,7 @@ class JestPlugin extends CiPlugin {
 
       this.telemetry.count(TELEMETRY_TEST_SESSION, {
         provider: this.ciProviderName,
-        autoInjected: !!getEnvironmentVariable('DD_CIVISIBILITY_AUTO_INSTRUMENTATION_PROVIDER')
+        autoInjected: !!getResolvedEnv('DD_CIVISIBILITY_AUTO_INSTRUMENTATION_PROVIDER')
       })
 
       this.tracer._exporter.flush(() => {
diff --git a/packages/datadog-plugin-mocha/src/index.js b/packages/datadog-plugin-mocha/src/index.js
index 5636dc99a01..b672ae51741 100644
--- a/packages/datadog-plugin-mocha/src/index.js
+++ b/packages/datadog-plugin-mocha/src/index.js
@@ -2,7 +2,7 @@
 
 const CiPlugin = require('../../dd-trace/src/plugins/ci_plugin')
 const { storage } = require('../../datadog-core')
-const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../dd-trace/src/config-env-sources')
 
 const {
   TEST_STATUS,
@@ -406,7 +406,7 @@ class MochaPlugin extends CiPlugin {
         finishAllTraceSpans(this.testSessionSpan)
         this.telemetry.count(TELEMETRY_TEST_SESSION, {
           provider: this.ciProviderName,
-          autoInjected: !!getEnvironmentVariable('DD_CIVISIBILITY_AUTO_INSTRUMENTATION_PROVIDER')
+          autoInjected: !!getResolvedEnv('DD_CIVISIBILITY_AUTO_INSTRUMENTATION_PROVIDER')
         })
       }
       this.libraryConfig = null
diff --git a/packages/datadog-plugin-mongodb-core/src/index.js b/packages/datadog-plugin-mongodb-core/src/index.js
index 2dcd801a119..856b44a931c 100644
--- a/packages/datadog-plugin-mongodb-core/src/index.js
+++ b/packages/datadog-plugin-mongodb-core/src/index.js
@@ -2,7 +2,7 @@
 
 const { isTrue } = require('../../dd-trace/src/util')
 const DatabasePlugin = require('../../dd-trace/src/plugins/database')
-const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../dd-trace/src/config-env-sources')
 
 class MongodbCorePlugin extends DatabasePlugin {
   static id = 'mongodb-core'
@@ -20,7 +20,7 @@ class MongodbCorePlugin extends DatabasePlugin {
   configure (config) {
     super.configure(config)
 
-    const heartbeatFromEnv = getEnvironmentVariable('DD_TRACE_MONGODB_HEARTBEAT_ENABLED')
+    const heartbeatFromEnv = getResolvedEnv('DD_TRACE_MONGODB_HEARTBEAT_ENABLED')
 
     this.config.heartbeatEnabled = config.heartbeatEnabled ??
       (heartbeatFromEnv && isTrue(heartbeatFromEnv)) ??
diff --git a/packages/datadog-plugin-playwright/src/index.js b/packages/datadog-plugin-playwright/src/index.js
index ca5d9c612d5..25251e3c1c2 100644
--- a/packages/datadog-plugin-playwright/src/index.js
+++ b/packages/datadog-plugin-playwright/src/index.js
@@ -3,7 +3,7 @@
 const { storage } = require('../../datadog-core')
 const id = require('../../dd-trace/src/id')
 const CiPlugin = require('../../dd-trace/src/plugins/ci_plugin')
-const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../dd-trace/src/config-env-sources')
 
 const {
   TEST_STATUS,
@@ -106,7 +106,7 @@ class PlaywrightPlugin extends CiPlugin {
       finishAllTraceSpans(this.testSessionSpan)
       this.telemetry.count(TELEMETRY_TEST_SESSION, {
         provider: this.ciProviderName,
-        autoInjected: !!getEnvironmentVariable('DD_CIVISIBILITY_AUTO_INSTRUMENTATION_PROVIDER')
+        autoInjected: !!getResolvedEnv('DD_CIVISIBILITY_AUTO_INSTRUMENTATION_PROVIDER')
       })
       appClosingTelemetry()
       this.tracer._exporter.flush(onDone)
@@ -393,7 +393,7 @@ class PlaywrightPlugin extends CiPlugin {
       span.finish()
 
       finishAllTraceSpans(span)
-      if (getEnvironmentVariable('DD_PLAYWRIGHT_WORKER')) {
+      if (getResolvedEnv('DD_PLAYWRIGHT_WORKER')) {
         this.tracer._exporter.flush(onDone)
       }
     })
diff --git a/packages/datadog-plugin-vitest/src/index.js b/packages/datadog-plugin-vitest/src/index.js
index eaed04c2624..db218a508ea 100644
--- a/packages/datadog-plugin-vitest/src/index.js
+++ b/packages/datadog-plugin-vitest/src/index.js
@@ -2,7 +2,7 @@
 
 const CiPlugin = require('../../dd-trace/src/plugins/ci_plugin')
 const { storage } = require('../../datadog-core')
-const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('../../dd-trace/src/config-env-sources')
 
 const {
   TEST_STATUS,
@@ -281,11 +281,11 @@ class VitestPlugin extends CiPlugin {
     this.addBind('ci:vitest:test-suite:start', (ctx) => {
       const { testSuiteAbsolutePath, frameworkVersion } = ctx
 
-      this.command = getEnvironmentVariable('DD_CIVISIBILITY_TEST_COMMAND')
+      this.command = getResolvedEnv('DD_CIVISIBILITY_TEST_COMMAND')
       this.frameworkVersion = frameworkVersion
       const testSessionSpanContext = this.tracer.extract('text_map', {
-        'x-datadog-trace-id': getEnvironmentVariable('DD_CIVISIBILITY_TEST_SESSION_ID'),
-        'x-datadog-parent-id': getEnvironmentVariable('DD_CIVISIBILITY_TEST_MODULE_ID')
+        'x-datadog-trace-id': getResolvedEnv('DD_CIVISIBILITY_TEST_SESSION_ID'),
+        'x-datadog-parent-id': getResolvedEnv('DD_CIVISIBILITY_TEST_MODULE_ID')
       })
 
       const trimmedCommand = DD_MAJOR < 6 ? this.command : 'vitest run'
@@ -405,7 +405,7 @@ class VitestPlugin extends CiPlugin {
       finishAllTraceSpans(this.testSessionSpan)
       this.telemetry.count(TELEMETRY_TEST_SESSION, {
         provider: this.ciProviderName,
-        autoInjected: !!getEnvironmentVariable('DD_CIVISIBILITY_AUTO_INSTRUMENTATION_PROVIDER')
+        autoInjected: !!getResolvedEnv('DD_CIVISIBILITY_AUTO_INSTRUMENTATION_PROVIDER')
       })
       this.tracer._exporter.flush(onFinish)
     })
diff --git a/packages/dd-trace/src/ci-visibility/early-flake-detection/get-known-tests.js b/packages/dd-trace/src/ci-visibility/early-flake-detection/get-known-tests.js
index 6f10be0ba9d..09caf516f92 100644
--- a/packages/dd-trace/src/ci-visibility/early-flake-detection/get-known-tests.js
+++ b/packages/dd-trace/src/ci-visibility/early-flake-detection/get-known-tests.js
@@ -3,7 +3,7 @@
 const request = require('../../exporters/common/request')
 const id = require('../../id')
 const log = require('../../log')
-const { getEnvironmentVariable } = require('../../config-helper')
+const { getResolvedEnv } = require('../../config-env-sources')
 
 const {
   incrementCountMetric,
@@ -51,7 +51,7 @@ function getKnownTests ({
     options.path = `${evpProxyPrefix}/api/v2/ci/libraries/tests`
     options.headers['X-Datadog-EVP-Subdomain'] = 'api'
   } else {
-    const apiKey = getEnvironmentVariable('DD_API_KEY')
+    const apiKey = getResolvedEnv('DD_API_KEY')
     if (!apiKey) {
       return done(new Error('Known tests were not fetched because Datadog API key is not defined.'))
     }
diff --git a/packages/dd-trace/src/ci-visibility/exporters/agentless/coverage-writer.js b/packages/dd-trace/src/ci-visibility/exporters/agentless/coverage-writer.js
index b3646d81cfe..3f606cab2c3 100644
--- a/packages/dd-trace/src/ci-visibility/exporters/agentless/coverage-writer.js
+++ b/packages/dd-trace/src/ci-visibility/exporters/agentless/coverage-writer.js
@@ -2,7 +2,7 @@
 const request = require('../../../exporters/common/request')
 const log = require('../../../log')
 const { safeJSONStringify } = require('../../../exporters/common/util')
-const { getEnvironmentVariable } = require('../../../config-helper')
+const { getResolvedEnv } = require('../../../config-env-sources')
 
 const { CoverageCIVisibilityEncoder } = require('../../../encode/coverage-ci-visibility')
 const BaseWriter = require('../../../exporters/common/writer')
@@ -29,7 +29,7 @@ class Writer extends BaseWriter {
       path: '/api/v2/citestcov',
       method: 'POST',
       headers: {
-        'dd-api-key': getEnvironmentVariable('DD_API_KEY'),
+        'dd-api-key': getResolvedEnv('DD_API_KEY'),
         ...form.getHeaders()
       },
       timeout: 15_000,
diff --git a/packages/dd-trace/src/ci-visibility/exporters/agentless/di-logs-writer.js b/packages/dd-trace/src/ci-visibility/exporters/agentless/di-logs-writer.js
index 199b2910e8b..b7f023b26c2 100644
--- a/packages/dd-trace/src/ci-visibility/exporters/agentless/di-logs-writer.js
+++ b/packages/dd-trace/src/ci-visibility/exporters/agentless/di-logs-writer.js
@@ -3,7 +3,7 @@ const request = require('../../../exporters/common/request')
 const log = require('../../../log')
 const { safeJSONStringify } = require('../../../exporters/common/util')
 const { JSONEncoder } = require('../../encode/json-encoder')
-const { getEnvironmentVariable } = require('../../../config-helper')
+const { getResolvedEnv } = require('../../../config-env-sources')
 
 const BaseWriter = require('../../../exporters/common/writer')
 
@@ -24,7 +24,7 @@ class DynamicInstrumentationLogsWriter extends BaseWriter {
       path: '/api/v2/logs',
       method: 'POST',
       headers: {
-        'dd-api-key': getEnvironmentVariable('DD_API_KEY'),
+        'dd-api-key': getResolvedEnv('DD_API_KEY'),
         'Content-Type': 'application/json'
       },
       // TODO: what's a good value for timeout for the logs intake?
diff --git a/packages/dd-trace/src/ci-visibility/exporters/agentless/writer.js b/packages/dd-trace/src/ci-visibility/exporters/agentless/writer.js
index f4e017a3e0e..e25f40632e7 100644
--- a/packages/dd-trace/src/ci-visibility/exporters/agentless/writer.js
+++ b/packages/dd-trace/src/ci-visibility/exporters/agentless/writer.js
@@ -2,7 +2,7 @@
 const request = require('../../../exporters/common/request')
 const { safeJSONStringify } = require('../../../exporters/common/util')
 const log = require('../../../log')
-const { getEnvironmentVariable } = require('../../../config-helper')
+const { getResolvedEnv } = require('../../../config-env-sources')
 
 const { AgentlessCiVisibilityEncoder } = require('../../../encode/agentless-ci-visibility')
 const BaseWriter = require('../../../exporters/common/writer')
@@ -30,7 +30,7 @@ class Writer extends BaseWriter {
       path: '/api/v2/citestcycle',
       method: 'POST',
       headers: {
-        'dd-api-key': getEnvironmentVariable('DD_API_KEY'),
+        'dd-api-key': getResolvedEnv('DD_API_KEY'),
         'Content-Type': 'application/msgpack'
       },
       timeout: 15_000,
diff --git a/packages/dd-trace/src/ci-visibility/exporters/git/git_metadata.js b/packages/dd-trace/src/ci-visibility/exporters/git/git_metadata.js
index 98ebed4e7c9..6eacaec4d1f 100644
--- a/packages/dd-trace/src/ci-visibility/exporters/git/git_metadata.js
+++ b/packages/dd-trace/src/ci-visibility/exporters/git/git_metadata.js
@@ -5,7 +5,7 @@ const path = require('path')
 
 const FormData = require('../../../exporters/common/form-data')
 const request = require('../../../exporters/common/request')
-const { getEnvironmentVariable } = require('../../../config-helper')
+const { getResolvedEnv } = require('../../../config-env-sources')
 
 const log = require('../../../log')
 const { isFalse } = require('../../../util')
@@ -51,7 +51,7 @@ function getCommonRequestOptions (url) {
   return {
     method: 'POST',
     headers: {
-      'dd-api-key': getEnvironmentVariable('DD_API_KEY')
+      'dd-api-key': getResolvedEnv('DD_API_KEY')
     },
     timeout: 15_000,
     url
@@ -288,7 +288,7 @@ function sendGitMetadata (url, { isEvpProxy, evpProxyPrefix }, configRepositoryU
     }
     // Otherwise we unshallow and get commits to upload again
     log.debug('It is shallow clone, unshallowing...')
-    if (!isFalse(getEnvironmentVariable('DD_CIVISIBILITY_GIT_UNSHALLOW_ENABLED'))) {
+    if (!isFalse(getResolvedEnv('DD_CIVISIBILITY_GIT_UNSHALLOW_ENABLED'))) {
       unshallowRepository(false)
     }
 
diff --git a/packages/dd-trace/src/ci-visibility/exporters/test-worker/index.js b/packages/dd-trace/src/ci-visibility/exporters/test-worker/index.js
index 5cd7e775387..6f05d83aa9b 100644
--- a/packages/dd-trace/src/ci-visibility/exporters/test-worker/index.js
+++ b/packages/dd-trace/src/ci-visibility/exporters/test-worker/index.js
@@ -26,6 +26,7 @@ function getInterprocessTraceCode () {
   if (getEnvironmentVariable('DD_PLAYWRIGHT_WORKER')) {
     return PLAYWRIGHT_WORKER_TRACE_PAYLOAD_CODE
   }
+  // ??
   if (getEnvironmentVariable('TINYPOOL_WORKER_ID')) {
     return VITEST_WORKER_TRACE_PAYLOAD_CODE
   }
diff --git a/packages/dd-trace/src/ci-visibility/intelligent-test-runner/get-skippable-suites.js b/packages/dd-trace/src/ci-visibility/intelligent-test-runner/get-skippable-suites.js
index ac7e0e1ee8b..a71cdc59212 100644
--- a/packages/dd-trace/src/ci-visibility/intelligent-test-runner/get-skippable-suites.js
+++ b/packages/dd-trace/src/ci-visibility/intelligent-test-runner/get-skippable-suites.js
@@ -2,7 +2,7 @@
 
 const request = require('../../exporters/common/request')
 const log = require('../../log')
-const { getEnvironmentVariable } = require('../../config-helper')
+const { getResolvedEnv } = require('../../config-env-sources')
 const {
   incrementCountMetric,
   distributionMetric,
@@ -49,7 +49,7 @@ function getSkippableSuites ({
     options.path = `${evpProxyPrefix}/api/v2/ci/tests/skippable`
     options.headers['X-Datadog-EVP-Subdomain'] = 'api'
   } else {
-    const apiKey = getEnvironmentVariable('DD_API_KEY')
+    const apiKey = getResolvedEnv('DD_API_KEY')
     if (!apiKey) {
       return done(new Error('Skippable suites were not fetched because Datadog API key is not defined.'))
     }
diff --git a/packages/dd-trace/src/ci-visibility/log-submission/log-submission-plugin.js b/packages/dd-trace/src/ci-visibility/log-submission/log-submission-plugin.js
index 1e0fd6550e7..e211c687758 100644
--- a/packages/dd-trace/src/ci-visibility/log-submission/log-submission-plugin.js
+++ b/packages/dd-trace/src/ci-visibility/log-submission/log-submission-plugin.js
@@ -2,7 +2,7 @@
 
 const Plugin = require('../../plugins/plugin')
 const log = require('../../log')
-const { getEnvironmentVariable } = require('../../config-helper')
+const { getResolvedEnv } = require('../../config-env-sources')
 
 function getWinstonLogSubmissionParameters (config) {
   const { site, service } = config
@@ -12,16 +12,16 @@ function getWinstonLogSubmissionParameters (config) {
     path: `/api/v2/logs?ddsource=winston&service=${service}`,
     ssl: true,
     headers: {
-      'DD-API-KEY': getEnvironmentVariable('DD_API_KEY')
+      'DD-API-KEY': getResolvedEnv('DD_API_KEY')
     }
   }
 
-  if (!getEnvironmentVariable('DD_AGENTLESS_LOG_SUBMISSION_URL')) {
+  if (!getResolvedEnv('DD_AGENTLESS_LOG_SUBMISSION_URL')) {
     return defaultParameters
   }
 
   try {
-    const url = new URL(getEnvironmentVariable('DD_AGENTLESS_LOG_SUBMISSION_URL'))
+    const url = new URL(getResolvedEnv('DD_AGENTLESS_LOG_SUBMISSION_URL'))
     return {
       host: url.hostname,
       port: url.port,
diff --git a/packages/dd-trace/src/ci-visibility/requests/get-library-configuration.js b/packages/dd-trace/src/ci-visibility/requests/get-library-configuration.js
index e16b62dcdfa..2c5ad36122f 100644
--- a/packages/dd-trace/src/ci-visibility/requests/get-library-configuration.js
+++ b/packages/dd-trace/src/ci-visibility/requests/get-library-configuration.js
@@ -3,7 +3,7 @@
 const request = require('../../exporters/common/request')
 const id = require('../../id')
 const log = require('../../log')
-const { getEnvironmentVariable } = require('../../config-helper')
+const { getResolvedEnv } = require('../../config-env-sources')
 const {
   incrementCountMetric,
   distributionMetric,
@@ -48,7 +48,7 @@ function getLibraryConfiguration ({
     options.path = `${evpProxyPrefix}/api/v2/libraries/tests/services/setting`
     options.headers['X-Datadog-EVP-Subdomain'] = 'api'
   } else {
-    const apiKey = getEnvironmentVariable('DD_API_KEY')
+    const apiKey = getResolvedEnv('DD_API_KEY')
     if (!apiKey) {
       return done(new Error('Request to settings endpoint was not done because Datadog API key is not defined.'))
     }
@@ -126,11 +126,11 @@ function getLibraryConfiguration ({
 
         log.debug('Remote settings: %j', settings)
 
-        if (getEnvironmentVariable('DD_CIVISIBILITY_DANGEROUSLY_FORCE_COVERAGE')) {
+        if (getResolvedEnv('DD_CIVISIBILITY_DANGEROUSLY_FORCE_COVERAGE')) {
           settings.isCodeCoverageEnabled = true
           log.debug('Dangerously set code coverage to true')
         }
-        if (getEnvironmentVariable('DD_CIVISIBILITY_DANGEROUSLY_FORCE_TEST_SKIPPING')) {
+        if (getResolvedEnv('DD_CIVISIBILITY_DANGEROUSLY_FORCE_TEST_SKIPPING')) {
           settings.isSuitesSkippingEnabled = true
           log.debug('Dangerously set test skipping to true')
         }
diff --git a/packages/dd-trace/src/ci-visibility/test-management/get-test-management-tests.js b/packages/dd-trace/src/ci-visibility/test-management/get-test-management-tests.js
index a6a8516efb6..db37bfa9b25 100644
--- a/packages/dd-trace/src/ci-visibility/test-management/get-test-management-tests.js
+++ b/packages/dd-trace/src/ci-visibility/test-management/get-test-management-tests.js
@@ -2,7 +2,7 @@
 
 const request = require('../../exporters/common/request')
 const id = require('../../id')
-const { getEnvironmentVariable } = require('../../config-helper')
+const { getResolvedEnv } = require('../../config-env-sources')
 const log = require('../../log')
 
 function getTestManagementTests ({
@@ -35,7 +35,7 @@ function getTestManagementTests ({
     options.path = `${evpProxyPrefix}/api/v2/test/libraries/test-management/tests`
     options.headers['X-Datadog-EVP-Subdomain'] = 'api'
   } else {
-    const apiKey = getEnvironmentVariable('DD_API_KEY')
+    const apiKey = getResolvedEnv('DD_API_KEY')
     if (!apiKey) {
       return done(new Error('Test management tests were not fetched because Datadog API key is not defined.'))
     }
diff --git a/packages/dd-trace/src/config-env-sources.js b/packages/dd-trace/src/config-env-sources.js
new file mode 100644
index 00000000000..79788389cc8
--- /dev/null
+++ b/packages/dd-trace/src/config-env-sources.js
@@ -0,0 +1,112 @@
+'use strict'
+
+const { isInServerlessEnvironment } = require('./serverless')
+const { getValueFromEnvSource, getEnvironmentVariable } = require('./config-helper')
+
+/**
+ * Internal helper that centralizes configuration coming from stable config files and environment variables.
+ *
+ * Responsibilities:
+ * - Load and parse the local and fleet stable configuration files (via `StableConfig`).
+ * - Expose the stable config maps (`localStableConfig`, `fleetStableConfig`) and any warnings
+ *   `stableConfigWarnings`.
+ * - Provide `getResolvedEnv(name)` to resolve a configuration value from:
+ *     1. Fleet stable config
+ *     2. Environment variables (and their aliases)
+ *     3. Local stable config
+ *
+ * Usage patterns:
+ * - Most modules that need a single resolved value should call `getResolvedEnv(name)`.
+ * - The main `Config` class reads `localStableConfig` / `fleetStableConfig` directly so it can:
+ *     - Preserve per-source origins (fleet/local/env) for telemetry reporting.
+ *     - Merge sources in its own priority order.
+ * - Tests can reset the singleton with `resetConfigEnvSources()` to force re-loading after
+ *   modifying stable config files or environment variables.
+ */
+class ConfigEnvSources {
+  constructor () {
+    const isServerless = isInServerlessEnvironment()
+
+    let localStableConfig = {}
+    let fleetStableConfig = {}
+    let stableConfigWarnings = []
+
+    if (!isServerless) {
+      const result = this.#loadStableConfig()
+      if (result) {
+        localStableConfig = result.localEntries
+        fleetStableConfig = result.fleetEntries
+        stableConfigWarnings = result.warnings
+      }
+    }
+
+    // Expose raw stable config on the instance
+    this.localStableConfig = localStableConfig
+    this.fleetStableConfig = fleetStableConfig
+    this.stableConfigWarnings = stableConfigWarnings
+  }
+
+  #loadStableConfig () {
+    try {
+      const StableConfig = require('./config_stable')
+      const instance = new StableConfig()
+      return {
+        localEntries: instance.localEntries ?? {},
+        fleetEntries: instance.fleetEntries ?? {},
+        warnings: instance.warnings ?? []
+      }
+    } catch {
+      // Stable config is optional, continue without it
+      return null
+    }
+  }
+}
+
+function createConfigEnvSources () {
+  return new ConfigEnvSources()
+}
+
+let configEnvSourcesInstance = null
+
+function getConfigEnvSources () {
+  if (!configEnvSourcesInstance) {
+    configEnvSourcesInstance = new ConfigEnvSources()
+  }
+  return configEnvSourcesInstance
+}
+
+/**
+ * Reset the singleton instance (useful for testing)
+ */
+function resetConfigEnvSources () {
+  configEnvSourcesInstance = null
+}
+
+/**
+ * Returns the resolved configuration value from ConfigEnvSources. Falls back to aliases if the
+ * canonical name is not set. Throws an error if the configuration is not supported.
+ *
+ * @param {string} name Environment variable name
+ * @returns {string|undefined}
+ * @throws {Error} if the configuration is not supported
+ */
+function getResolvedEnv (name) {
+  const config = getConfigEnvSources()
+  if (getValueFromEnvSource(name, config.fleetStableConfig) !== undefined) {
+    return getValueFromEnvSource(name, config.fleetStableConfig)
+  }
+  if (getEnvironmentVariable(name) !== undefined) {
+    return getEnvironmentVariable(name)
+  }
+  if (getValueFromEnvSource(name, config.localStableConfig) !== undefined) {
+    return getValueFromEnvSource(name, config.localStableConfig)
+  }
+}
+
+module.exports = {
+  ConfigEnvSources,
+  createConfigEnvSources,
+  getConfigEnvSources,
+  resetConfigEnvSources,
+  getResolvedEnv
+}
diff --git a/packages/dd-trace/src/config-helper.js b/packages/dd-trace/src/config-helper.js
index eb457fcc959..448c9b14e89 100644
--- a/packages/dd-trace/src/config-helper.js
+++ b/packages/dd-trace/src/config-helper.js
@@ -80,10 +80,9 @@ module.exports = {
    * @returns {string|undefined}
    * @throws {Error} if the configuration is not supported
    */
-  // This method, and callers of this method, need to be updated to check for declarative config sources as well.
   getEnvironmentVariable (name) {
     if ((name.startsWith('DD_') || name.startsWith('OTEL_') || aliasToCanonical[name]) &&
-        !supportedConfigurations[name]) {
+      !supportedConfigurations[name]) {
       throw new Error(`Missing ${name} env/configuration in "supported-configurations.json" file.`)
     }
     const config = process.env[name]
@@ -95,5 +94,31 @@ module.exports = {
       }
     }
     return config
+  },
+
+  /**
+   * Returns the value stored at the given name, assumed to be in environment variable format,
+   * from the provided source. Falls back to aliases if the canonical name is not set.
+   * Used for stable config sources.
+   *
+   * @param {string} name Environment variable name
+   * @param {object} source Environment source
+   * @returns {string|undefined}
+   * @throws {Error} if the configuration is not supported
+   */
+  getValueFromEnvSource (name, source) {
+    if ((name.startsWith('DD_') || name.startsWith('OTEL_') || aliasToCanonical[name]) &&
+      !supportedConfigurations[name]) {
+      throw new Error(`Missing ${name} env/configuration in "supported-configurations.json" file.`)
+    }
+    const value = source[name]
+    if (value === undefined && aliases[name]) {
+      for (const alias of aliases[name]) {
+        if (source[alias] !== undefined) {
+          return source[alias]
+        }
+      }
+    }
+    return value
   }
 }
diff --git a/packages/dd-trace/src/config.js b/packages/dd-trace/src/config.js
index 898877e5f36..0c16716349e 100644
--- a/packages/dd-trace/src/config.js
+++ b/packages/dd-trace/src/config.js
@@ -18,6 +18,7 @@ const { isInServerlessEnvironment, getIsGCPFunction, getIsAzureFunction } = requ
 const { ORIGIN_KEY } = require('./constants')
 const { appendRules } = require('./payload-tagging/config')
 const { getEnvironmentVariable: getEnv, getEnvironmentVariables } = require('./config-helper')
+const { getConfigEnvSources } = require('./config-env-sources')
 const defaults = require('./config_defaults')
 const path = require('path')
 const { DD_MAJOR } = require('../../../version')
@@ -272,8 +273,12 @@ class Config {
   constructor (options = {}) {
     if (!isInServerlessEnvironment()) {
       // Bail out early if we're in a serverless environment, stable config isn't supported
-      const StableConfig = require('./config_stable')
-      this.stableConfig = new StableConfig()
+      const configEnvSources = getConfigEnvSources()
+      this.stableConfig = {
+        fleetEntries: configEnvSources.fleetStableConfig,
+        localEntries: configEnvSources.localStableConfig,
+        warnings: configEnvSources.stableConfigWarnings
+      }
     }
 
     const envs = getEnvironmentVariables()
diff --git a/packages/dd-trace/src/debugger/devtools_client/send.js b/packages/dd-trace/src/debugger/devtools_client/send.js
index b0a66c84737..99956c3f380 100644
--- a/packages/dd-trace/src/debugger/devtools_client/send.js
+++ b/packages/dd-trace/src/debugger/devtools_client/send.js
@@ -9,7 +9,7 @@ const request = require('../../exporters/common/request')
 const { GIT_COMMIT_SHA, GIT_REPOSITORY_URL } = require('../../plugins/util/tags')
 const log = require('./log')
 const { version } = require('../../../../../package.json')
-const { getEnvironmentVariable } = require('../../config-helper')
+const { getResolvedEnv } = require('../../config-env-sources')
 
 module.exports = send
 
@@ -22,8 +22,8 @@ const hostname = getHostname()
 const service = config.service
 
 const ddtags = [
-  ['env', getEnvironmentVariable('DD_ENV')],
-  ['version', getEnvironmentVariable('DD_VERSION')],
+  ['env', getResolvedEnv('DD_ENV')],
+  ['version', getResolvedEnv('DD_VERSION')],
   ['debugger_version', version],
   ['host_name', hostname],
   [GIT_COMMIT_SHA, config.commitSHA],
diff --git a/packages/dd-trace/src/encode/0.4.js b/packages/dd-trace/src/encode/0.4.js
index b8f40f45e48..8272647e367 100644
--- a/packages/dd-trace/src/encode/0.4.js
+++ b/packages/dd-trace/src/encode/0.4.js
@@ -5,7 +5,7 @@ const { MsgpackChunk, MsgpackEncoder } = require('../msgpack')
 const log = require('../log')
 const { isTrue } = require('../util')
 const { memoize } = require('../log/utils')
-const { getEnvironmentVariable } = require('../config-helper')
+const { getResolvedEnv } = require('../config-env-sources')
 
 const SOFT_LIMIT = 8 * 1024 * 1024 // 8MB
 
@@ -31,7 +31,7 @@ class AgentEncoder {
     this._stringBytes = new MsgpackChunk()
     this._writer = writer
     this._reset()
-    this._debugEncoding = isTrue(getEnvironmentVariable('DD_TRACE_ENCODING_DEBUG'))
+    this._debugEncoding = isTrue(getResolvedEnv('DD_TRACE_ENCODING_DEBUG'))
     this._config = this._writer?._config
   }
 
diff --git a/packages/dd-trace/src/exporters/common/docker.js b/packages/dd-trace/src/exporters/common/docker.js
index b7d14b353bb..26c7eab7de9 100644
--- a/packages/dd-trace/src/exporters/common/docker.js
+++ b/packages/dd-trace/src/exporters/common/docker.js
@@ -1,9 +1,9 @@
 'use strict'
 
 const fs = require('fs')
-const { getEnvironmentVariable } = require('../../config-helper')
+const { getResolvedEnv } = require('../../config-env-sources')
 
-const DD_EXTERNAL_ENV = getEnvironmentVariable('DD_EXTERNAL_ENV')
+const DD_EXTERNAL_ENV = getResolvedEnv('DD_EXTERNAL_ENV')
 
 // The second part is the PCF / Garden regexp. We currently assume no suffix($) to avoid matching pod UIDs
 // See https://github.com/DataDog/datadog-agent/blob/7.40.x/pkg/util/cgroups/reader.go#L50
diff --git a/packages/dd-trace/src/exporters/common/util.js b/packages/dd-trace/src/exporters/common/util.js
index 5dd66c43726..d7f733e0d0d 100644
--- a/packages/dd-trace/src/exporters/common/util.js
+++ b/packages/dd-trace/src/exporters/common/util.js
@@ -1,12 +1,12 @@
 'use strict'
 
-const { getEnvironmentVariable } = require('../../config-helper')
+const { getResolvedEnv } = require('../../config-env-sources')
 
 function safeJSONStringify (value) {
   return JSON.stringify(
     value,
     (key, value) => key === 'dd-api-key' ? undefined : value,
-    getEnvironmentVariable('DD_TRACE_BEAUTIFUL_LOGS') ? 2 : undefined
+    getResolvedEnv('DD_TRACE_BEAUTIFUL_LOGS') ? 2 : undefined
   )
 }
 
diff --git a/packages/dd-trace/src/index.js b/packages/dd-trace/src/index.js
index f83890f241c..af71db3ca37 100644
--- a/packages/dd-trace/src/index.js
+++ b/packages/dd-trace/src/index.js
@@ -1,14 +1,14 @@
 'use strict'
 
 const { isFalse } = require('./util')
-const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('./config-env-sources')
 
 // Global `jest` is only present in Jest workers.
 const inJestWorker = typeof jest !== 'undefined'
 
-const ddTraceDisabled = getEnvironmentVariable('DD_TRACE_ENABLED')
-  ? isFalse(getEnvironmentVariable('DD_TRACE_ENABLED'))
-  : String(getEnvironmentVariable('OTEL_TRACES_EXPORTER')).toLowerCase() === 'none'
+const ddTraceDisabled = getResolvedEnv('DD_TRACE_ENABLED')
+  ? isFalse(getResolvedEnv('DD_TRACE_ENABLED'))
+  : String(getResolvedEnv('OTEL_TRACES_EXPORTER')).toLowerCase() === 'none'
 
 module.exports = ddTraceDisabled || inJestWorker
   ? require('./noop/proxy')
diff --git a/packages/dd-trace/src/lambda/handler.js b/packages/dd-trace/src/lambda/handler.js
index 4a4f9fa653e..9c2626a00bf 100644
--- a/packages/dd-trace/src/lambda/handler.js
+++ b/packages/dd-trace/src/lambda/handler.js
@@ -4,7 +4,7 @@ const log = require('../log')
 const { channel } = require('../../../datadog-instrumentations/src/helpers/instrument')
 const { ERROR_MESSAGE, ERROR_TYPE } = require('../constants')
 const { ImpendingTimeout } = require('./runtime/errors')
-const { getEnvironmentVariable } = require('../config-helper')
+const { getResolvedEnv } = require('../config-env-sources')
 
 const globalTracer = global._ddtrace
 const tracer = globalTracer._tracer
@@ -26,7 +26,7 @@ let __lambdaTimeout
 function checkTimeout (context) {
   const remainingTimeInMillis = context.getRemainingTimeInMillis()
 
-  let apmFlushDeadline = Number.parseInt(getEnvironmentVariable('DD_APM_FLUSH_DEADLINE_MILLISECONDS')) || 100
+  let apmFlushDeadline = Number.parseInt(getResolvedEnv('DD_APM_FLUSH_DEADLINE_MILLISECONDS')) || 100
   apmFlushDeadline = apmFlushDeadline < 0 ? 100 : apmFlushDeadline
 
   __lambdaTimeout = setTimeout(() => {
diff --git a/packages/dd-trace/src/lambda/index.js b/packages/dd-trace/src/lambda/index.js
index ce0a5d783c9..018af13340a 100644
--- a/packages/dd-trace/src/lambda/index.js
+++ b/packages/dd-trace/src/lambda/index.js
@@ -1,13 +1,13 @@
 'use strict'
 
 const { registerLambdaHook } = require('./runtime/ritm')
-const { getEnvironmentVariable } = require('../config-helper')
+const { getResolvedEnv } = require('../config-env-sources')
 
 /**
  * It is safe to do it this way, since customers will never be expected to disable
  * this specific instrumentation through the init config object.
  */
-const _DD_TRACE_DISABLED_INSTRUMENTATIONS = getEnvironmentVariable('DD_TRACE_DISABLED_INSTRUMENTATIONS') || ''
+const _DD_TRACE_DISABLED_INSTRUMENTATIONS = getResolvedEnv('DD_TRACE_DISABLED_INSTRUMENTATIONS') || ''
 const _disabledInstrumentations = new Set(
   _DD_TRACE_DISABLED_INSTRUMENTATIONS ? _DD_TRACE_DISABLED_INSTRUMENTATIONS.split(',') : []
 )
diff --git a/packages/dd-trace/src/llmobs/sdk.js b/packages/dd-trace/src/llmobs/sdk.js
index 87cf98ea120..95f2f276944 100644
--- a/packages/dd-trace/src/llmobs/sdk.js
+++ b/packages/dd-trace/src/llmobs/sdk.js
@@ -14,7 +14,7 @@ const Span = require('../opentracing/span')
 
 const tracerVersion = require('../../../../package.json').version
 const logger = require('../log')
-const { getEnvironmentVariable } = require('../config-helper')
+const { getResolvedEnv } = require('../config-env-sources')
 const telemetry = require('./telemetry')
 
 const LLMObsTagger = require('./tagger')
@@ -55,7 +55,7 @@ class LLMObs extends NoopLLMObs {
 
     const { mlApp, agentlessEnabled } = options
 
-    const DD_LLMOBS_ENABLED = getEnvironmentVariable('DD_LLMOBS_ENABLED')
+    const DD_LLMOBS_ENABLED = getResolvedEnv('DD_LLMOBS_ENABLED')
 
     const llmobsConfig = {
       mlApp,
diff --git a/packages/dd-trace/src/opentracing/span.js b/packages/dd-trace/src/opentracing/span.js
index 41c0988c82f..0c6a5afefcf 100644
--- a/packages/dd-trace/src/opentracing/span.js
+++ b/packages/dd-trace/src/opentracing/span.js
@@ -13,17 +13,17 @@ const { storage } = require('../../../datadog-core')
 const telemetryMetrics = require('../telemetry/metrics')
 const { channel } = require('dc-polyfill')
 const util = require('util')
-const { getEnvironmentVariable } = require('../config-helper')
+const { getResolvedEnv } = require('../config-env-sources')
 
 const tracerMetrics = telemetryMetrics.manager.namespace('tracers')
 
-const DD_TRACE_EXPERIMENTAL_STATE_TRACKING = getEnvironmentVariable('DD_TRACE_EXPERIMENTAL_STATE_TRACKING')
-const DD_TRACE_EXPERIMENTAL_SPAN_COUNTS = getEnvironmentVariable('DD_TRACE_EXPERIMENTAL_SPAN_COUNTS')
+const DD_TRACE_EXPERIMENTAL_STATE_TRACKING = getResolvedEnv('DD_TRACE_EXPERIMENTAL_STATE_TRACKING')
+const DD_TRACE_EXPERIMENTAL_SPAN_COUNTS = getResolvedEnv('DD_TRACE_EXPERIMENTAL_SPAN_COUNTS')
 
 const unfinishedRegistry = createRegistry('unfinished')
 const finishedRegistry = createRegistry('finished')
 
-const OTEL_ENABLED = !!getEnvironmentVariable('DD_TRACE_OTEL_ENABLED')
+const OTEL_ENABLED = !!getResolvedEnv('DD_TRACE_OTEL_ENABLED')
 const ALLOWED = new Set(['string', 'number', 'boolean'])
 
 const integrationCounters = {
diff --git a/packages/dd-trace/src/plugin_manager.js b/packages/dd-trace/src/plugin_manager.js
index 337330d4ba5..79fe8339b40 100644
--- a/packages/dd-trace/src/plugin_manager.js
+++ b/packages/dd-trace/src/plugin_manager.js
@@ -5,6 +5,7 @@ const { isFalse, isTrue, normalizePluginEnvName } = require('./util')
 const plugins = require('./plugins')
 const log = require('./log')
 const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('./config-env-sources')
 
 // Test optimization plugins that should only be enabled when isCiVisibility is true
 const TEST_OPTIMIZATION_PLUGINS = new Set([
@@ -24,7 +25,7 @@ if (getEnvironmentVariable('AWS_LAMBDA_FUNCTION_NAME') !== undefined) {
   require('./lambda')
 }
 
-const DD_TRACE_DISABLED_PLUGINS = getEnvironmentVariable('DD_TRACE_DISABLED_PLUGINS')
+const DD_TRACE_DISABLED_PLUGINS = getResolvedEnv('DD_TRACE_DISABLED_PLUGINS')
 
 const disabledPlugins = new Set(
   DD_TRACE_DISABLED_PLUGINS && DD_TRACE_DISABLED_PLUGINS.split(',').map(plugin => plugin.trim())
@@ -41,7 +42,7 @@ loadChannel.subscribe(({ name }) => {
 function maybeEnable (Plugin) {
   if (!Plugin || typeof Plugin !== 'function') return
   if (!pluginClasses[Plugin.id]) {
-    const enabled = getEnvEnabled(Plugin)
+    const enabled = getEnabled(Plugin)
 
     // TODO: remove the need to load the plugin class in order to disable the plugin
     if (isFalse(enabled) || disabledPlugins.has(Plugin.id)) {
@@ -54,9 +55,9 @@ function maybeEnable (Plugin) {
   }
 }
 
-function getEnvEnabled (Plugin) {
+function getEnabled (Plugin) {
   const envName = `DD_TRACE_${Plugin.id.toUpperCase()}_ENABLED`
-  return getEnvironmentVariable(normalizePluginEnvName(envName))
+  return getResolvedEnv(normalizePluginEnvName(envName))
 }
 
 // TODO this must always be a singleton.
@@ -94,7 +95,8 @@ module.exports = class PluginManager {
       this._pluginsByName[name] = new Plugin(this._tracer, this._tracerConfig)
     }
     const pluginConfig = this._configsByName[name] || {
-      enabled: this._tracerConfig.plugins !== false && (!Plugin.experimental || isTrue(getEnvEnabled(Plugin)))
+      enabled: this._tracerConfig.plugins !== false &&
+        (!Plugin.experimental || isTrue(getEnabled(Plugin)))
     }
 
     // extracts predetermined configuration from tracer and combines it with plugin-specific config
diff --git a/packages/dd-trace/src/plugins/util/git-cache.js b/packages/dd-trace/src/plugins/util/git-cache.js
index 0dfc99d40da..324b9483dca 100644
--- a/packages/dd-trace/src/plugins/util/git-cache.js
+++ b/packages/dd-trace/src/plugins/util/git-cache.js
@@ -7,11 +7,11 @@ const crypto = require('crypto')
 const cp = require('child_process')
 
 const log = require('../../log')
-const { getEnvironmentVariable } = require('../../config-helper')
+const { getResolvedEnv } = require('../../config-env-sources')
 const { isTrue } = require('../../util')
 
-let isGitEnabled = isTrue(getEnvironmentVariable('DD_EXPERIMENTAL_TEST_OPT_GIT_CACHE_ENABLED'))
-const GIT_CACHE_DIR = getEnvironmentVariable('DD_EXPERIMENTAL_TEST_OPT_GIT_CACHE_DIR') ||
+let isGitEnabled = isTrue(getResolvedEnv('DD_EXPERIMENTAL_TEST_OPT_GIT_CACHE_ENABLED'))
+const GIT_CACHE_DIR = getResolvedEnv('DD_EXPERIMENTAL_TEST_OPT_GIT_CACHE_DIR') ||
   path.join(os.tmpdir(), 'dd-trace-git-cache')
 
 function ensureCacheDir () {
diff --git a/packages/dd-trace/src/profiling/exporter_cli.js b/packages/dd-trace/src/profiling/exporter_cli.js
index 564877aa319..0c3c44a9c98 100644
--- a/packages/dd-trace/src/profiling/exporter_cli.js
+++ b/packages/dd-trace/src/profiling/exporter_cli.js
@@ -8,7 +8,7 @@ const { ConsoleLogger } = require('./loggers/console')
 const { tagger } = require('./tagger')
 const fs = require('fs')
 const { fileURLToPath } = require('url')
-const { getEnvironmentVariable } = require('../config-helper')
+const { getResolvedEnv } = require('../config-env-sources')
 
 const logger = new ConsoleLogger()
 const timeoutMs = 15 * 1000
@@ -17,9 +17,9 @@ function exporterFromURL (url) {
   if (url.protocol === 'file:') {
     return new FileExporter({ pprofPrefix: fileURLToPath(url) })
   }
-  const injectionEnabled = (getEnvironmentVariable('DD_INJECTION_ENABLED') ?? '').split(',')
+  const injectionEnabled = (getResolvedEnv('DD_INJECTION_ENABLED') ?? '').split(',')
   const libraryInjected = injectionEnabled.length > 0
-  const profilingEnabled = (getEnvironmentVariable('DD_PROFILING_ENABLED') ?? '').toLowerCase()
+  const profilingEnabled = (getResolvedEnv('DD_PROFILING_ENABLED') ?? '').toLowerCase()
   const activation = ['true', '1'].includes(profilingEnabled)
     ? 'manual'
     : profilingEnabled === 'auto'
diff --git a/packages/dd-trace/src/proxy.js b/packages/dd-trace/src/proxy.js
index 321117f9fa7..7e7ef6bdd12 100644
--- a/packages/dd-trace/src/proxy.js
+++ b/packages/dd-trace/src/proxy.js
@@ -10,7 +10,7 @@ const telemetry = require('./telemetry')
 const nomenclature = require('./service-naming')
 const PluginManager = require('./plugin_manager')
 const NoopDogStatsDClient = require('./noop/dogstatsd')
-const { getEnvironmentVariable } = require('../../dd-trace/src/config-helper')
+const { getResolvedEnv } = require('./config-env-sources')
 const {
   setBaggageItem,
   getBaggageItem,
@@ -202,7 +202,7 @@ class Tracer extends NoopProxy {
         this._testApiManualPlugin.configure({ ...config, enabled: true }, false)
       }
       if (config.ciVisAgentlessLogSubmissionEnabled) {
-        if (getEnvironmentVariable('DD_API_KEY')) {
+        if (getResolvedEnv('DD_API_KEY')) {
           const LogSubmissionPlugin = require('./ci-visibility/log-submission/log-submission-plugin')
           const automaticLogPlugin = new LogSubmissionPlugin(this)
           automaticLogPlugin.configure({ ...config, enabled: true })
diff --git a/packages/dd-trace/src/runtime_metrics/runtime_metrics.js b/packages/dd-trace/src/runtime_metrics/runtime_metrics.js
index fc9cb546adc..40471ce784e 100644
--- a/packages/dd-trace/src/runtime_metrics/runtime_metrics.js
+++ b/packages/dd-trace/src/runtime_metrics/runtime_metrics.js
@@ -8,12 +8,12 @@ const process = require('process')
 const { DogStatsDClient, MetricsAggregationClient } = require('../dogstatsd')
 const log = require('../log')
 const { performance, PerformanceObserver, monitorEventLoopDelay } = require('perf_hooks')
-const { getEnvironmentVariable } = require('../config-helper')
+const { getResolvedEnv } = require('../config-env-sources')
 
 const { NODE_MAJOR } = require('../../../../version')
 // TODO: This environment variable may not be changed, since the agent expects a flush every ten seconds.
 // It is only a variable for testing. Think about alternatives.
-const DD_RUNTIME_METRICS_FLUSH_INTERVAL = getEnvironmentVariable('DD_RUNTIME_METRICS_FLUSH_INTERVAL') ?? '10000'
+const DD_RUNTIME_METRICS_FLUSH_INTERVAL = getResolvedEnv('DD_RUNTIME_METRICS_FLUSH_INTERVAL') ?? '10000'
 const INTERVAL = Number.parseInt(DD_RUNTIME_METRICS_FLUSH_INTERVAL, 10)
 
 const eventLoopDelayResolution = 4
diff --git a/packages/dd-trace/src/span_processor.js b/packages/dd-trace/src/span_processor.js
index bc3231016ee..8aee2c1f187 100644
--- a/packages/dd-trace/src/span_processor.js
+++ b/packages/dd-trace/src/span_processor.js
@@ -4,7 +4,7 @@ const log = require('./log')
 const spanFormat = require('./span_format')
 const SpanSampler = require('./span_sampler')
 const GitMetadataTagger = require('./git_metadata_tagger')
-const { getEnvironmentVariable } = require('./config-helper')
+const { getResolvedEnv } = require('./config-env-sources')
 
 const startedSpans = new WeakSet()
 const finishedSpans = new WeakSet()
@@ -83,7 +83,7 @@ class SpanProcessor {
   }
 
   _erase (trace, active) {
-    if (getEnvironmentVariable('DD_TRACE_EXPERIMENTAL_STATE_TRACKING') === 'true') {
+    if (getResolvedEnv('DD_TRACE_EXPERIMENTAL_STATE_TRACKING') === 'true') {
       const started = new Set()
       const startedIds = new Set()
       const finished = new Set()
diff --git a/packages/dd-trace/src/telemetry/send-data.js b/packages/dd-trace/src/telemetry/send-data.js
index 43851f63583..3cad7402d89 100644
--- a/packages/dd-trace/src/telemetry/send-data.js
+++ b/packages/dd-trace/src/telemetry/send-data.js
@@ -3,7 +3,7 @@
 const request = require('../exporters/common/request')
 const log = require('../log')
 const { isTrue } = require('../util')
-const { getEnvironmentVariable } = require('../config-helper')
+const { getResolvedEnv } = require('../config-env-sources')
 
 let agentTelemetry = true
 
@@ -54,7 +54,7 @@ function sendData (config, application, host, reqType, payload = {}, cb = () =>
   let url = config.url
 
   const isCiVisibilityAgentlessMode = isCiVisibility &&
-                                      isTrue(getEnvironmentVariable('DD_CIVISIBILITY_AGENTLESS_ENABLED'))
+                                      isTrue(getResolvedEnv('DD_CIVISIBILITY_AGENTLESS_ENABLED'))
 
   if (isCiVisibilityAgentlessMode) {
     try {
@@ -88,14 +88,14 @@ function sendData (config, application, host, reqType, payload = {}, cb = () =>
   })
 
   request(data, options, (error) => {
-    if (error && getEnvironmentVariable('DD_API_KEY') && config.site) {
+    if (error && getResolvedEnv('DD_API_KEY') && config.site) {
       if (agentTelemetry) {
         log.warn('Agent telemetry failed, started agentless telemetry')
         agentTelemetry = false
       }
       // figure out which data center to send to
       const backendUrl = getAgentlessTelemetryEndpoint(config.site)
-      const backendHeader = { ...options.headers, 'DD-API-KEY': getEnvironmentVariable('DD_API_KEY') }
+      const backendHeader = { ...options.headers, 'DD-API-KEY': getResolvedEnv('DD_API_KEY') }
       const backendOptions = {
         ...options,
         url: backendUrl,
diff --git a/packages/dd-trace/test/config-env-sources.spec.js b/packages/dd-trace/test/config-env-sources.spec.js
new file mode 100644
index 00000000000..012c8e1acd4
--- /dev/null
+++ b/packages/dd-trace/test/config-env-sources.spec.js
@@ -0,0 +1,444 @@
+'use strict'
+
+const { expect } = require('chai')
+const sinon = require('sinon')
+const { it, describe, beforeEach, afterEach } = require('tap').mocha
+const proxyquire = require('proxyquire')
+
+require('./setup/core')
+
+describe('ConfigEnvSources', () => {
+  let ConfigEnvSources
+  let createConfigEnvSources
+  let getConfigEnvSources
+  let resetConfigEnvSources
+  let isInServerlessEnvironmentStub
+  let StableConfigStub
+
+  beforeEach(() => {
+    // Reset stubs
+    isInServerlessEnvironmentStub = sinon.stub()
+    StableConfigStub = sinon.stub()
+
+    // Load module with stubs
+    const mod = proxyquire('../src/config-env-sources', {
+      './serverless': {
+        isInServerlessEnvironment: isInServerlessEnvironmentStub
+      },
+      './config_stable': StableConfigStub
+    })
+
+    ConfigEnvSources = mod.ConfigEnvSources
+    createConfigEnvSources = mod.createConfigEnvSources
+    getConfigEnvSources = mod.getConfigEnvSources
+    resetConfigEnvSources = mod.resetConfigEnvSources
+
+    // Reset singleton
+    resetConfigEnvSources()
+  })
+
+  afterEach(() => {
+    sinon.restore()
+    resetConfigEnvSources()
+  })
+
+  describe('constructor', () => {
+    it('should load stable config when not in serverless environment', () => {
+      isInServerlessEnvironmentStub.returns(false)
+
+      // Mock stable config with local and fleet entries
+      StableConfigStub.callsFake(function () {
+        this.localEntries = {
+          DD_SERVICE: 'local-service',
+          DD_ENV: 'local-env',
+          DD_VERSION: 'local-version'
+        }
+        this.fleetEntries = {
+          DD_SERVICE: 'fleet-service',
+          DD_ENV: 'fleet-env'
+        }
+        this.warnings = []
+      })
+
+      const sources = new ConfigEnvSources()
+
+      expect(StableConfigStub.calledOnce).to.be.true
+      expect(sources.localStableConfig).to.deep.equal({
+        DD_SERVICE: 'local-service',
+        DD_ENV: 'local-env',
+        DD_VERSION: 'local-version'
+      })
+      expect(sources.fleetStableConfig).to.deep.equal({
+        DD_SERVICE: 'fleet-service',
+        DD_ENV: 'fleet-env'
+      })
+    })
+
+    it('should not load stable config in serverless environment', () => {
+      isInServerlessEnvironmentStub.returns(true)
+
+      const sources = new ConfigEnvSources()
+
+      // StableConfig should not be called
+      expect(StableConfigStub.called).to.be.false
+      expect(sources.localStableConfig).to.deep.equal({})
+      expect(sources.fleetStableConfig).to.deep.equal({})
+    })
+
+    it('should handle empty or missing stable config entries', () => {
+      isInServerlessEnvironmentStub.returns(false)
+
+      StableConfigStub.callsFake(function () {
+        this.localEntries = null
+        this.fleetEntries = undefined
+        this.warnings = []
+      })
+
+      const sources = new ConfigEnvSources()
+
+      expect(sources.localStableConfig).to.deep.equal({})
+      expect(sources.fleetStableConfig).to.deep.equal({})
+    })
+  })
+
+  describe('createConfigEnvSources', () => {
+    it('should create a new ConfigEnvSources instance', () => {
+      isInServerlessEnvironmentStub.returns(true)
+
+      const sources1 = createConfigEnvSources()
+      const sources2 = createConfigEnvSources()
+
+      expect(sources1).to.be.instanceof(ConfigEnvSources)
+      expect(sources2).to.be.instanceof(ConfigEnvSources)
+      expect(sources1).to.not.equal(sources2)
+    })
+  })
+
+  describe('getConfigEnvSources', () => {
+    it('should return a singleton instance', () => {
+      isInServerlessEnvironmentStub.returns(true)
+
+      const sources1 = getConfigEnvSources()
+      const sources2 = getConfigEnvSources()
+
+      expect(sources1).to.be.instanceof(ConfigEnvSources)
+      expect(sources1).to.equal(sources2)
+    })
+
+    it('should create instance only once', () => {
+      isInServerlessEnvironmentStub.returns(false)
+
+      StableConfigStub.callsFake(function () {
+        this.localEntries = {}
+        this.fleetEntries = {}
+        this.warnings = []
+      })
+
+      getConfigEnvSources()
+      getConfigEnvSources()
+      getConfigEnvSources()
+
+      // StableConfig should only be instantiated once
+      expect(StableConfigStub.callCount).to.equal(1)
+    })
+  })
+
+  describe('resetConfigEnvSources', () => {
+    it('should reset the singleton instance', () => {
+      isInServerlessEnvironmentStub.returns(true)
+
+      const sources1 = getConfigEnvSources()
+      resetConfigEnvSources()
+      const sources2 = getConfigEnvSources()
+
+      expect(sources1).to.not.equal(sources2)
+    })
+
+    it('should allow fresh instance creation with updated values', () => {
+      isInServerlessEnvironmentStub.returns(false)
+
+      StableConfigStub.onCall(0).callsFake(function () {
+        this.localEntries = {
+          DD_SERVICE: 'service-1'
+        }
+        this.fleetEntries = {}
+        this.warnings = []
+      })
+
+      StableConfigStub.onCall(1).callsFake(function () {
+        this.localEntries = {
+          DD_SERVICE: 'service-2'
+        }
+        this.fleetEntries = {}
+        this.warnings = []
+      })
+
+      const sources1 = getConfigEnvSources()
+      expect(sources1.localStableConfig.DD_SERVICE).to.equal('service-1')
+
+      resetConfigEnvSources()
+
+      const sources2 = getConfigEnvSources()
+      expect(sources2.localStableConfig.DD_SERVICE).to.equal('service-2')
+    })
+  })
+})
+
+describe('getResolvedEnv', () => {
+  let getResolvedEnv
+  let resetConfigEnvSources
+  let isInServerlessEnvironmentStub
+  let originalEnv
+
+  beforeEach(() => {
+    isInServerlessEnvironmentStub = sinon.stub().returns(true)
+    originalEnv = process.env
+    process.env = { ...originalEnv }
+
+    const configEnvSourcesMod = proxyquire('../src/config-env-sources', {
+      './serverless': {
+        isInServerlessEnvironment: isInServerlessEnvironmentStub
+      }
+    })
+
+    resetConfigEnvSources = configEnvSourcesMod.resetConfigEnvSources
+    getResolvedEnv = configEnvSourcesMod.getResolvedEnv
+
+    // Reset singleton
+    resetConfigEnvSources()
+  })
+
+  afterEach(() => {
+    sinon.restore()
+    resetConfigEnvSources()
+    process.env = originalEnv
+  })
+
+  it('should return value from ConfigEnvSources for supported configuration', () => {
+    process.env.DD_SERVICE = 'my-service'
+    process.env.DD_ENV = 'production'
+
+    const value = getResolvedEnv('DD_SERVICE')
+
+    expect(value).to.equal('my-service')
+  })
+
+  it('should fall back to alias if canonical name is not set', () => {
+    process.env.DD_TRACE_AGENT_HOSTNAME = 'alias-hostname'
+
+    // DD_AGENT_HOST is the canonical name, DD_TRACE_AGENT_HOSTNAME is an alias
+    const value = getResolvedEnv('DD_AGENT_HOST')
+
+    expect(value).to.equal('alias-hostname')
+  })
+
+  it('should return undefined if neither canonical nor alias is set', () => {
+    process.env.DD_SERVICE = 'my-service'
+
+    const value = getResolvedEnv('DD_ENV')
+
+    expect(value).to.be.undefined
+  })
+
+  it('should prefer canonical name over alias', () => {
+    process.env.DD_AGENT_HOST = 'canonical-hostname'
+    process.env.DD_TRACE_AGENT_HOSTNAME = 'alias-hostname'
+
+    const value = getResolvedEnv('DD_AGENT_HOST')
+
+    expect(value).to.equal('canonical-hostname')
+  })
+
+  it('should throw error for unsupported DD_ configuration', () => {
+    expect(() => {
+      getResolvedEnv('DD_UNSUPPORTED_CONFIG')
+    }).to.throw('Missing DD_UNSUPPORTED_CONFIG env/configuration in "supported-configurations.json" file.')
+  })
+
+  it('should throw error for unsupported OTEL_ configuration', () => {
+    expect(() => {
+      getResolvedEnv('OTEL_UNSUPPORTED_CONFIG')
+    }).to.throw('Missing OTEL_UNSUPPORTED_CONFIG env/configuration in "supported-configurations.json" file.')
+  })
+
+  it('should return value for non-DD/OTEL environment variables', () => {
+    process.env.NODE_ENV = 'production'
+    process.env.PATH = '/usr/bin'
+
+    const value = getResolvedEnv('NODE_ENV')
+
+    expect(value).to.equal('production')
+  })
+
+  it('should use singleton ConfigEnvSources instance', () => {
+    isInServerlessEnvironmentStub.returns(true)
+    process.env.DD_SERVICE = 'my-service'
+
+    getResolvedEnv('DD_SERVICE')
+    getResolvedEnv('DD_ENV')
+
+    // ConfigEnvSources should only be instantiated once (isInServerlessEnvironment called once)
+    expect(isInServerlessEnvironmentStub.callCount).to.equal(1)
+  })
+
+  it('should work with merged values from stable config and env vars', () => {
+    const StableConfigStub = sinon.stub()
+    StableConfigStub.callsFake(function () {
+      this.localEntries = {
+        DD_SERVICE: 'local-service'
+      }
+      this.fleetEntries = {
+        DD_SERVICE: 'fleet-service'
+      }
+      this.warnings = []
+    })
+
+    const isInServerlessStub = sinon.stub().returns(false)
+    process.env.DD_ENV = 'production'
+
+    // Re-setup with stable config stub
+    resetConfigEnvSources()
+    const configEnvSourcesMod = proxyquire('../src/config-env-sources', {
+      './serverless': {
+        isInServerlessEnvironment: isInServerlessStub
+      },
+      './config_stable': StableConfigStub
+    })
+
+    const getResolvedEnvFn = configEnvSourcesMod.getResolvedEnv
+
+    // Fleet should win for DD_SERVICE
+    expect(getResolvedEnvFn('DD_SERVICE')).to.equal('fleet-service')
+    // Env var should be used for DD_ENV
+    expect(getResolvedEnvFn('DD_ENV')).to.equal('production')
+  })
+
+  describe('priority scenarios', () => {
+    it('should prioritize fleet over env over local', () => {
+      const StableConfigStub = sinon.stub()
+      StableConfigStub.callsFake(function () {
+        this.localEntries = {
+          DD_TRACE_SAMPLE_RATE: '0.1',
+          DD_TRACE_ENABLED: 'false',
+          DD_SERVICE: 'local'
+        }
+        this.fleetEntries = {
+          DD_TRACE_SAMPLE_RATE: '0.9',
+          DD_SERVICE: 'fleet'
+        }
+        this.warnings = []
+      })
+
+      const isInServerlessStub = sinon.stub().returns(false)
+
+      process.env.DD_TRACE_SAMPLE_RATE = '0.5'
+      process.env.DD_TRACE_ENABLED = 'true'
+
+      resetConfigEnvSources()
+      const configEnvSourcesMod = proxyquire('../src/config-env-sources', {
+        './serverless': {
+          isInServerlessEnvironment: isInServerlessStub
+        },
+        './config_stable': StableConfigStub
+      })
+
+      const getResolvedEnvFn = configEnvSourcesMod.getResolvedEnv
+
+      // Fleet wins
+      expect(getResolvedEnvFn('DD_TRACE_SAMPLE_RATE')).to.equal('0.9')
+      expect(getResolvedEnvFn('DD_SERVICE')).to.equal('fleet')
+      // Env wins (not in fleet)
+      expect(getResolvedEnvFn('DD_TRACE_ENABLED')).to.equal('true')
+    })
+
+    it('should not override defined values with undefined', () => {
+      const StableConfigStub = sinon.stub()
+      StableConfigStub.callsFake(function () {
+        this.localEntries = {
+          DD_SERVICE: 'local-service'
+        }
+        this.fleetEntries = {
+          DD_SERVICE: undefined
+        }
+        this.warnings = []
+      })
+
+      const isInServerlessStub = sinon.stub().returns(false)
+
+      // Env var is not set (undefined)
+
+      resetConfigEnvSources()
+      const configEnvSourcesMod = proxyquire('../src/config-env-sources', {
+        './serverless': {
+          isInServerlessEnvironment: isInServerlessStub
+        },
+        './config_stable': StableConfigStub
+      })
+
+      const getResolvedEnvFn = configEnvSourcesMod.getResolvedEnv
+
+      // Local value should remain since higher priorities are undefined
+      expect(getResolvedEnvFn('DD_SERVICE')).to.equal('local-service')
+    })
+  })
+
+  describe('compatibility with getEnvironmentVariable', () => {
+    it('should return env var values when no stable config exists (serverless)', () => {
+      // Set up env without stable config (serverless mode)
+      isInServerlessEnvironmentStub.returns(true)
+      process.env.DD_SERVICE = 'my-service'
+      process.env.DD_ENV = 'production'
+      process.env.DD_TRACE_AGENT_PORT = '8126'
+
+      resetConfigEnvSources()
+      const configEnvSourcesMod = proxyquire('../src/config-env-sources', {
+        './serverless': {
+          isInServerlessEnvironment: isInServerlessEnvironmentStub
+        }
+      })
+
+      const getResolvedEnvFn = configEnvSourcesMod.getResolvedEnv
+
+      // Should return the env var values directly (no stable config involved)
+      expect(getResolvedEnvFn('DD_SERVICE')).to.equal('my-service')
+      expect(getResolvedEnvFn('DD_ENV')).to.equal('production')
+      expect(getResolvedEnvFn('DD_TRACE_AGENT_PORT')).to.equal('8126')
+    })
+
+    it('should return undefined for unset values', () => {
+      isInServerlessEnvironmentStub.returns(true)
+      process.env.DD_SERVICE = 'my-service'
+
+      resetConfigEnvSources()
+      const configEnvSourcesMod = proxyquire('../src/config-env-sources', {
+        './serverless': {
+          isInServerlessEnvironment: isInServerlessEnvironmentStub
+        }
+      })
+
+      const getResolvedEnvFn = configEnvSourcesMod.getResolvedEnv
+
+      // Should return undefined for unset supported config
+      expect(getResolvedEnvFn('DD_ENV')).to.be.undefined
+      expect(getResolvedEnvFn('DD_VERSION')).to.be.undefined
+    })
+
+    it('should throw same error for unsupported configuration', () => {
+      isInServerlessEnvironmentStub.returns(true)
+
+      resetConfigEnvSources()
+      const configEnvSourcesMod = proxyquire('../src/config-env-sources', {
+        './serverless': {
+          isInServerlessEnvironment: isInServerlessEnvironmentStub
+        }
+      })
+
+      const getResolvedEnvFn = configEnvSourcesMod.getResolvedEnv
+
+      // Both should throw for unsupported DD_ vars
+      expect(() => getResolvedEnvFn('DD_UNSUPPORTED_VAR')).to.throw(
+        'Missing DD_UNSUPPORTED_VAR env/configuration in "supported-configurations.json" file.'
+      )
+    })
+  })
+})
diff --git a/packages/dd-trace/test/config.spec.js b/packages/dd-trace/test/config.spec.js
index 42dd9ff9250..effb4a10951 100644
--- a/packages/dd-trace/test/config.spec.js
+++ b/packages/dd-trace/test/config.spec.js
@@ -14,6 +14,7 @@ require('./setup/core')
 
 const { GRPC_CLIENT_ERROR_STATUSES, GRPC_SERVER_ERROR_STATUSES } = require('../src/constants')
 const { getEnvironmentVariable, getEnvironmentVariables } = require('../src/config-helper')
+const { resetConfigEnvSources } = require('../src/config-env-sources')
 const { assertObjectContains } = require('../../../integration-tests/helpers')
 const { DD_MAJOR } = require('../../../version')
 
@@ -2819,6 +2820,7 @@ describe('Config', () => {
       tempDir = fs.mkdtempSync(path.join(baseTempDir, 'config-test-'))
       process.env.DD_TEST_LOCAL_CONFIG_PATH = path.join(tempDir, 'local.yaml')
       process.env.DD_TEST_FLEET_CONFIG_PATH = path.join(tempDir, 'fleet.yaml')
+      resetConfigEnvSources()
     })
 
     afterEach(() => {
@@ -2872,6 +2874,8 @@ rules:
     configuration:
       DD_SERVICE: service_local_stable
 `)
+      resetConfigEnvSources()
+
       const config2 = getConfig()
       expect(config2).to.have.property(
         'service',
@@ -2881,6 +2885,8 @@ rules:
 
       // 3. Env > Local stable > Default
       process.env.DD_SERVICE = 'service_env'
+      resetConfigEnvSources()
+
       const config3 = getConfig()
       expect(config3).to.have.property(
         'service',
@@ -2901,6 +2907,7 @@ rules:
     configuration:
       DD_SERVICE: service_fleet_stable
 `)
+      resetConfigEnvSources()
       const config4 = getConfig()
       expect(config4).to.have.property(
         'service',
@@ -3040,6 +3047,7 @@ apm_configuration_default:
   DD_TRACE_CLOUD_REQUEST_PAYLOAD_TAGGING: "all"
   DD_TRACE_CLOUD_PAYLOAD_TAGGING_MAX_DEPTH: 5
 `)
+      resetConfigEnvSources()
       let config = getConfig()
       expect(config).to.have.property('apiKey', 'local-api-key')
       expect(config).to.have.property('appKey', 'local-app-key')
@@ -3054,6 +3062,7 @@ apm_configuration_default:
       process.env.DD_APP_KEY = 'env-app-key'
       process.env.DD_INSTRUMENTATION_INSTALL_ID = 'env-install-id'
       process.env.DD_TRACE_CLOUD_PAYLOAD_TAGGING_MAX_DEPTH = '7'
+      resetConfigEnvSources()
       config = getConfig()
       expect(config).to.have.property('apiKey', 'env-api-key')
       expect(config).to.have.property('appKey', 'env-app-key')
@@ -3080,6 +3089,7 @@ rules:
       DD_TRACE_CLOUD_RESPONSE_PAYLOAD_TAGGING: "all"
       DD_TRACE_CLOUD_PAYLOAD_TAGGING_MAX_DEPTH: 15
 `)
+      resetConfigEnvSources()
       config = getConfig()
       expect(config).to.have.property('apiKey', 'fleet-api-key')
       expect(config).to.have.property('appKey', 'fleet-app-key')
diff --git a/packages/dd-trace/test/plugin_manager.spec.js b/packages/dd-trace/test/plugin_manager.spec.js
index 027ad218707..bb8335e1ab9 100644
--- a/packages/dd-trace/test/plugin_manager.spec.js
+++ b/packages/dd-trace/test/plugin_manager.spec.js
@@ -81,6 +81,11 @@ describe('Plugin Manager', () => {
         getEnvironmentVariable (name) {
           return process.env[name]
         }
+      },
+      './config-env-sources': {
+        getResolvedEnv (name) {
+          return process.env[name]
+        }
       }
     })
     pm = new PluginManager(tracer)