diff --git a/apps/server/package.json b/apps/server/package.json
index c63836d95d5..87e98ada112 100644
--- a/apps/server/package.json
+++ b/apps/server/package.json
@@ -25,7 +25,7 @@
     "typecheck": "tsc --noEmit",
     "test": "vitest run",
     "test:process-reaper": "vitest run src/server.test.ts src/provider/Layers/ClaudeAdapter.test.ts src/provider/Layers/ProviderSessionDirectory.test.ts src/provider/Layers/ProviderSessionReaper.test.ts src/provider/Layers/CodexAdapter.test.ts",
-    "test:perf": "vitest run integration/perf"
+    "test:perf": "VITEST_PERF=1 vitest run integration/perf"
   },
   "dependencies": {
     "@anthropic-ai/claude-agent-sdk": "^0.2.111",
diff --git a/apps/server/src/provider/Layers/ClaudeAdapter.ts b/apps/server/src/provider/Layers/ClaudeAdapter.ts
index 7ea4b6be2b4..9bf918aaebe 100644
--- a/apps/server/src/provider/Layers/ClaudeAdapter.ts
+++ b/apps/server/src/provider/Layers/ClaudeAdapter.ts
@@ -42,12 +42,12 @@ import {
   TurnId,
   type UserInputQuestion,
   ClaudeCodeEffort,
+  type ModelCapabilities,
   RuntimeMode,
 } from "@t3tools/contracts";
 import {
   applyClaudePromptEffortPrefix,
   resolveApiModelId,
-  resolveEffort,
   trimOrNull,
 } from "@t3tools/shared/model";
 import {
@@ -222,12 +222,36 @@ function isSyntheticClaudeThreadId(value: string): boolean {
 }
 
 function getEffectiveClaudeCodeEffort(
-  effort: ClaudeCodeEffort | null | undefined,
+  caps: ModelCapabilities,
+  rawEffort: string | null | undefined,
 ): Exclude<ClaudeCodeEffort, "ultrathink"> | null {
-  if (!effort) {
+  const promptInjected = new Set(caps.promptInjectedEffortLevels);
+  const supportedNonPromptLevels = caps.reasoningEffortLevels
+    .map((level) => level.value)
+    .filter((value) => !promptInjected.has(value));
+
+  const trimmed = trimOrNull(rawEffort);
+
+  if (trimmed && supportedNonPromptLevels.includes(trimmed)) {
+    return trimmed as Exclude<ClaudeCodeEffort, "ultrathink">;
+  }
+
+  if (!trimmed) {
+    const defaultValue = caps.reasoningEffortLevels.find((level) => level.isDefault)?.value;
+    return defaultValue && !promptInjected.has(defaultValue)
+      ? (defaultValue as Exclude<ClaudeCodeEffort, "ultrathink">)
+      : null;
+  }
+
+  // Raw effort is unsupported (e.g. "max" on Sonnet 4.6) or prompt-injected
+  // (e.g. "ultrathink"); cap to the highest supported non-prompt-injected level.
+  if (supportedNonPromptLevels.length === 0) {
     return null;
   }
-  return effort === "ultrathink" ? null : effort;
+  return supportedNonPromptLevels[supportedNonPromptLevels.length - 1] as Exclude<
+    ClaudeCodeEffort,
+    "ultrathink"
+  >;
 }
 
 function isClaudeInterruptedMessage(message: string): boolean {
@@ -2927,14 +2951,12 @@ const makeClaudeAdapter = Effect.fn("makeClaudeAdapter")(function* (
         input.modelSelection?.provider === "claudeAgent" ? input.modelSelection : undefined;
       const caps = getClaudeModelCapabilities(modelSelection?.model);
       const apiModelId = modelSelection ? resolveApiModelId(modelSelection) : undefined;
-      const effort = (resolveEffort(caps, modelSelection?.options?.effort) ??
-        null) as ClaudeCodeEffort | null;
       const fastMode = modelSelection?.options?.fastMode === true && caps.supportsFastMode;
       const thinking =
         typeof modelSelection?.options?.thinking === "boolean" && caps.supportsThinkingToggle
           ? modelSelection.options.thinking
           : undefined;
-      const effectiveEffort = getEffectiveClaudeCodeEffort(effort);
+      const effectiveEffort = getEffectiveClaudeCodeEffort(caps, modelSelection?.options?.effort);
       const runtimeModeToPermission: Record<RuntimeMode, PermissionMode> = {
         "approval-required": "default",
         "auto-accept-edits": "acceptEdits",
diff --git a/apps/server/vitest.config.ts b/apps/server/vitest.config.ts
index 1c5b2f0d38d..2df4e464fd3 100644
--- a/apps/server/vitest.config.ts
+++ b/apps/server/vitest.config.ts
@@ -1,7 +1,11 @@
-import { defineConfig, mergeConfig } from "vitest/config";
+import { configDefaults, defineConfig, mergeConfig } from "vitest/config";
 
 import baseConfig from "../../vitest.config";
 
+// Perf benchmarks are wall-clock sensitive and unreliable on shared CI hardware.
+// `bun run test:perf` opts back in by setting VITEST_PERF=1.
+const includePerf = process.env.VITEST_PERF === "1";
+
 export default mergeConfig(
   baseConfig,
   defineConfig({
@@ -13,6 +17,9 @@ export default mergeConfig(
       // Under package-wide parallel runs they regularly exceed the default 15s budget.
       testTimeout: 60_000,
       hookTimeout: 60_000,
+      exclude: includePerf
+        ? [...configDefaults.exclude]
+        : [...configDefaults.exclude, "integration/perf/**"],
     },
   }),
 );