Expose per-combo reasoning token buffer toggle (#6702)

* fix(combos): default reasoning token buffer off

* feat(combos): expose reasoning token buffer toggle

* fix(combos): keep reasoning-token buffer default enabled, opt-out toggle

#6702 shipped bundled with #6536's own commit (identical SHA
37ac38f17f), flipping the combo-wide reasoningTokenBufferEnabled
default from true to false. #6536 was subsequently closed by the
author in favor of #6714, which explicitly keeps the existing
default-enabled buffer behavior and instead clamps the buffer to the
model's known output cap. Reconciled #6702 with that resolution:
dropped the default-flip changes across comboConfig.ts, combo.ts,
comboSetup.ts, ComboDefaultsTab.tsx, and the combo-defaults settings
route (plus their test assertions), and inverted the new per-combo
ReasoningTokenBufferToggle to opt-out semantics (`!== false`) so an
existing combo's behavior is unchanged unless the operator explicitly
unchecks it.

Co-authored-by: diegosouzapw <8016841+diegosouzapw@users.noreply.github.com>

---------

Co-authored-by: Diego Rodrigues de Sa e Souza <diegosouza.pw@gmail.com>
Co-authored-by: diegosouzapw <8016841+diegosouzapw@users.noreply.github.com>

CHANGELOG.md

@@ -11,6 +11,7 @@ _Living section — bullets land here as PRs merge into `release/v3.8.47` (paral
 ### ✨ New Features
 
 - **Provider/model param filters**: config-driven parameter denylist/allowlist per provider/model with auto-learn from upstream 400s (#6649 — thanks @ThongAccount, closes #6625)
+- **Per-combo reasoning token buffer toggle**: the combo builder now exposes an explicit checkbox for the `#3587` reasoning-model `max_tokens` buffer, defaulting to the existing enabled behavior, so a combo can opt out without hand-editing raw JSON config (#6702 — thanks @xz-dev)
 
 ### 🐛 Bug Fixes
 

open-sse/services/combo.ts

@@ -3032,7 +3032,10 @@ async function handleRoundRobinCombo({
           resilienceSettings.providerCooldown.enabled &&
           provider &&
           provider !== "unknown" &&
-          !(result.status === 500 && hasPerModelQuota(provider, parseModel(modelStr).model || modelStr))
+          !(
+            result.status === 500 &&
+            hasPerModelQuota(provider, parseModel(modelStr).model || modelStr)
+          )
         ) {
           recordProviderCooldown(
             provider,

open-sse/services/combo/comboSetup.ts

@@ -90,9 +90,7 @@ export function phaseComboSetup(ctx: ComboContext): ComboSetup {
 
   const universalHandoffConfig = resolveUniversalHandoffConfig(
     (combo.universal_handoff || combo.universalHandoff) as
-      | Record<string, unknown>
-      | null
-      | undefined,
+      Record<string, unknown> | null | undefined,
     relayOptions?.universalHandoffConfig as Record<string, unknown> | null | undefined
   );
 

src/app/(dashboard)/dashboard/combos/ReasoningTokenBufferToggle.tsx

@@ -0,0 +1,52 @@
+import Tooltip from "@/shared/components/Tooltip";
+
+type TranslationFn = {
+  (key: string): string;
+  has?: (key: string) => boolean;
+};
+
+type Props = {
+  config: Record<string, any>;
+  setConfig: (config: Record<string, any>) => void;
+  t: TranslationFn;
+};
+
+function getI18nOrFallback(t: TranslationFn, key: string, fallback: string): string {
+  try {
+    if (typeof t.has === "function" && t.has(key)) return t(key);
+  } catch {}
+  return fallback;
+}
+
+export default function ReasoningTokenBufferToggle({ config, setConfig, t }: Props) {
+  return (
+    <div className="flex items-center gap-2 py-1">
+      <input
+        type="checkbox"
+        id="reasoningTokenBufferEnabled"
+        data-testid="combo-reasoning-token-buffer-enabled"
+        checked={config.reasoningTokenBufferEnabled !== false}
+        onChange={(e) => setConfig({ ...config, reasoningTokenBufferEnabled: e.target.checked })}
+        className="w-3.5 h-3.5 rounded border border-black/20 dark:border-white/20 accent-primary cursor-pointer"
+      />
+      <label
+        htmlFor="reasoningTokenBufferEnabled"
+        className="text-xs text-text-muted cursor-pointer select-none"
+      >
+        {getI18nOrFallback(t, "reasoningTokenBuffer", "Reasoning token buffer")}
+      </label>
+      <Tooltip
+        position="bottom"
+        content={getI18nOrFallback(
+          t,
+          "advancedHelp.reasoningTokenBuffer",
+          "When enabled (default), OmniRoute may increase max_tokens for reasoning-capable models so they have headroom to think. Turn this off if you need this combo to preserve the client's exact max_tokens."
+        )}
+      >
+        <span className="material-symbols-outlined text-[12px] text-text-muted cursor-help">
+          help
+        </span>
+      </Tooltip>
+    </div>
+  );
+}

src/app/(dashboard)/dashboard/combos/page.tsx

@@ -15,6 +15,7 @@ import Tooltip from "@/shared/components/Tooltip";
 import { useCopyToClipboard } from "@/shared/hooks/useCopyToClipboard";
 import { FieldLabelWithHelp, WeightTotalBar } from "./parts";
 import { ResponseValidationEditor, type ResponseValidationValue } from "./ResponseValidationEditor";
+import ReasoningTokenBufferToggle from "./ReasoningTokenBufferToggle";
 import { pickDisplayValue } from "@/shared/utils/maskEmail";
 import useEmailPrivacyStore from "@/store/emailPrivacyStore";
 import { useNotificationStore } from "@/store/notificationStore";
@@ -217,10 +218,6 @@ function sanitizeComboRuntimeConfig(config) {
   );
 }
 
-// Build the next combo config when a Fusion tuning field changes. Prunes empty /
-// non-finite entries and drops the whole `fusionTuning` object when no field is
-// set, so an empty `{}` is never persisted (sanitizeComboRuntimeConfig keeps any
-// non-null object as-is).
 function updateFusionTuning(config, field, rawValue) {
   const value = rawValue === "" ? undefined : Number(rawValue);
   const next = { ...(config.fusionTuning || {}), [field]: value };
@@ -522,9 +519,7 @@ function getStrategyBadgeClass(strategy) {
 function getI18nOrFallback(t, key, fallback) {
   try {
     if (typeof t.has === "function" && t.has(key)) return t(key);
-  } catch {
-    // Some translations require ICU variables; fallback keeps optional helper text safe.
-  }
+  } catch {}
   return fallback;
 }
 
@@ -1023,7 +1018,6 @@ export default function CombosPage() {
 
   return (
     <div className="flex flex-col gap-6">
-      {/* Header */}
       <div className="flex flex-col gap-3 md:flex-row md:items-center md:justify-between">
         <div>
           <h1 className="text-2xl font-semibold">{t("title")}</h1>
@@ -2063,7 +2057,6 @@ function ComboFormModal({ isOpen, combo, onClose, onSave, activeProviders, combo
     }
   }, [builderStage, comboBuilderStages]);
 
-  // DnD state
   const hasPricingForModel = useCallback(
     (modelValue) => {
       const parsed = parseQualifiedModel(modelValue);
@@ -2752,9 +2745,7 @@ function ComboFormModal({ isOpen, combo, onClose, onSave, activeProviders, combo
       saveData.description = null;
     }
 
-    // Include config only if any values are set
     const configToSave = sanitizeComboRuntimeConfig(config);
-    // Add round-robin specific fields to config
     if (strategy === "round-robin") {
       if (config.concurrencyPerModel !== undefined)
         configToSave.concurrencyPerModel = config.concurrencyPerModel;
@@ -3740,7 +3731,6 @@ function ComboFormModal({ isOpen, combo, onClose, onSave, activeProviders, combo
                       />
                     </div>
                   </div>
-                  {/* failoverBeforeRetry + maxSetRetries + setRetryDelayMs */}
                   <div className="grid grid-cols-2 gap-2 pt-2 border-t border-black/5 dark:border-white/5">
                     <div className="col-span-2">
                       <div className="flex items-center gap-2 py-1">
@@ -3776,6 +3766,9 @@ function ComboFormModal({ isOpen, combo, onClose, onSave, activeProviders, combo
                         </Tooltip>
                       </div>
                     </div>
+                    <div className="col-span-2">
+                      <ReasoningTokenBufferToggle config={config} setConfig={setConfig} t={t} />
+                    </div>
                     <div>
                       <FieldLabelWithHelp
                         label={t("maxSetRetries")}
@@ -4166,7 +4159,11 @@ function ComboFormModal({ isOpen, combo, onClose, onSave, activeProviders, combo
                       </div>
                       <div>
                         <FieldLabelWithHelp
-                          label={getI18nOrFallback(t, "fusionStragglerGraceMs", "Straggler grace (ms)")}
+                          label={getI18nOrFallback(
+                            t,
+                            "fusionStragglerGraceMs",
+                            "Straggler grace (ms)"
+                          )}
                           help={getI18nOrFallback(
                             t,
                             "fusionStragglerGraceMsHelp",
@@ -4181,7 +4178,9 @@ function ComboFormModal({ isOpen, combo, onClose, onSave, activeProviders, combo
                           value={config.fusionTuning?.stragglerGraceMs ?? ""}
                           placeholder="8000"
                           onChange={(e) =>
-                            setConfig(updateFusionTuning(config, "stragglerGraceMs", e.target.value))
+                            setConfig(
+                              updateFusionTuning(config, "stragglerGraceMs", e.target.value)
+                            )
                           }
                           className="w-full text-xs py-1.5 px-2 rounded border border-black/10 dark:border-white/10 bg-transparent focus:border-primary focus:outline-none"
                         />
@@ -4580,7 +4579,6 @@ function ComboFormModal({ isOpen, combo, onClose, onSave, activeProviders, combo
             </div>
           )}
 
-          {/* Actions */}
           {isExpertMode ? (
             <div className="flex gap-2 pt-1">
               <Button onClick={onClose} variant="ghost" fullWidth size="sm">

src/app/(dashboard)/dashboard/settings/components/ComboDefaultsTab.tsx

@@ -292,8 +292,7 @@ export default function ComboDefaultsTab() {
 
   // Filtered provider list — excludes already-added ones, filtered by search query
   const filteredProviders = availableProviders.filter(
-    (p) =>
-      !providerOverrides[p.provider] && matchesSearch(p.provider, searchQuery)
+    (p) => !providerOverrides[p.provider] && matchesSearch(p.provider, searchQuery)
   );
 
   const handleDropdownKeyDown = (e: React.KeyboardEvent) => {