diff --git a/CHANGELOG.md b/CHANGELOG.md
index a0e5bea5fd..887c91f7f6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -31,6 +31,7 @@
 
 ### 🐛 Bug Fixes
 
+- **fix(dashboard):** adding a second API key connection for the same provider no longer silently overwrites the first — the Add-API-key modal now derives a unique default connection name (`main`, then `main-2`, `main-3`, …) so the backend name-based upsert can't collide (#6499 — thanks @dilneiss).
 - **fix(compression):** the session-dedup engine now also deduplicates a large multi-line block repeated **within a single message** (intra-message dedup), not just across turns; the compression-preview API surfaces a `fallbackReason`, and the fusion panel reports how many models were rate-limited vs failed on total-panel failure (#6501 — thanks @chirag127).
 - **fix(compression):** a stacked-pipeline step naming an unregistered engine now surfaces a `validationErrors` entry instead of silently no-op'ing, so misconfigured pipelines are visible in the preview API (#6506 — thanks @chirag127).
 - **feat(usage):** add a **Codex reset-credit redemption** flow to the Provider Limits UI — a `useCodexResetCreditRedemption` hook + `/api/usage/codex-reset-credit` route + `codexResetCredits` lib let you redeem banked Codex reset credits from the quota card. Regression guard: `tests/unit/codex-reset-credits.test.ts`. (thanks @JxnLexn)
diff --git a/config/quality/file-size-baseline.json b/config/quality/file-size-baseline.json
index 6ffd2b05e0..2988ff4d08 100644
--- a/config/quality/file-size-baseline.json
+++ b/config/quality/file-size-baseline.json
@@ -201,7 +201,7 @@
     "src/app/(dashboard)/dashboard/playground/components/tabs/ApiTab.tsx": 847,
     "src/app/(dashboard)/dashboard/providers/[id]/ProviderDetailPageClient.tsx": 784,
     "src/app/(dashboard)/dashboard/providers/[id]/components/ConnectionRow.tsx": 942,
-    "src/app/(dashboard)/dashboard/providers/[id]/components/modals/AddApiKeyModal.tsx": 952,
+    "src/app/(dashboard)/dashboard/providers/[id]/components/modals/AddApiKeyModal.tsx": 959,
     "src/app/(dashboard)/dashboard/providers/[id]/components/modals/EditConnectionModal.tsx": 1278,
     "src/app/(dashboard)/dashboard/providers/[id]/hooks/useProviderConnections.ts": 954,
     "src/app/(dashboard)/dashboard/providers/[id]/hooks/useProviderModels.ts": 155,
@@ -378,5 +378,6 @@
   "_rebaseline_2026_07_05_6235_doubao_dola": "PR #6235 own growth: tests/unit/web-cookie-providers-new.test.ts 850->890 (+40 = doubao-web -> Dola global provider switch regression cases: new host/cookie-domain/token-source assertions for www.dola.com). Cohesive test growth alongside the provider switch; contributor backryun. Fast-path PR->release skips check:file-size, so this bump lands with the PR.",
   "_rebaseline_2026_07_06_v3845_release_close": "Release v3.8.45 cycle-close rebaseline (captain, sess ce897453): 13 files grown by the cycle's merged fix/feature PRs (#6216 streaming fixes + request-logger UI grew RequestLoggerV2/chat/chatHelpers/auth/stream/response-sanitizer.test; #6251/#6253 dashboard UX grew combos page/modals/wizard/ComboDefaultsTab/ProxyRegistryManager/providerPageHelpers). Growth is legitimate merged-feature code, absorbed at release per Phase 0 drift policy; all remain frozen (cannot grow further).",
   "_rebaseline_2026_07_06_6118_zed_oauthmodal": "PR #6118 own growth: OAuthModal.tsx 989->993 (+4 = Zed hosted native-app sign-in modal branch). Cohesive UI growth for the zed-hosted OAuth provider; not extractable. The prior 6118 comment set the note but left the frozen value at 989.",
-  "_rebaseline_2026_07_06_6351_glm_team_quota": "PR #6351 own growth (GLM team-plan quota fields threaded through the connection modals; new GlmTeamQuotaFields.tsx extracted): AddApiKeyModal.tsx ->951 (+9), EditConnectionModal.tsx ->1277 (+18). Absorbs the pre-existing session base-red on these frozen modals; release captain rebaseline-at-release supersedes."
+  "_rebaseline_2026_07_06_6351_glm_team_quota": "PR #6351 own growth (GLM team-plan quota fields threaded through the connection modals; new GlmTeamQuotaFields.tsx extracted): AddApiKeyModal.tsx ->951 (+9), EditConnectionModal.tsx ->1277 (+18). Absorbs the pre-existing session base-red on these frozen modals; release captain rebaseline-at-release supersedes.",
+  "_rebaseline_2026_07_06_6499_unique_default_name": "PR #6499 own growth: AddApiKeyModal.tsx 952->959 (+7 = a unique default connection name so a second API key for the same provider does not reuse 'main' and trigger the backend name-based upsert that silently overwrote the first connection). The pure name derivation was extracted to computeConnectionDefaultName.ts (unit-tested) to keep the growth minimal; the contributor's original full-form-reset rewrite was trimmed to a spread reset to avoid dropping the GLM team-quota fields #6351 added and to hold the frozen god-file growth down. Release captain rebaseline-at-release supersedes."
 }
diff --git a/src/app/(dashboard)/dashboard/providers/[id]/ProviderDetailPageClient.tsx b/src/app/(dashboard)/dashboard/providers/[id]/ProviderDetailPageClient.tsx
index efbb574fe2..e460af15d7 100644
--- a/src/app/(dashboard)/dashboard/providers/[id]/ProviderDetailPageClient.tsx
+++ b/src/app/(dashboard)/dashboard/providers/[id]/ProviderDetailPageClient.tsx
@@ -709,6 +709,7 @@ export default function ProviderDetailPageClient() {
         isCommandCode={isCommandCode}
         isUpstreamProxyProvider={isUpstreamProxyProvider}
         subscriptionRisk={subscriptionRisk}
+        existingConnectionCount={connections.length}
         showRiskNoticeModal={showRiskNoticeModal}
         handleConfirmRiskNotice={handleConfirmRiskNotice}
         handleCancelRiskNotice={handleCancelRiskNotice}
diff --git a/src/app/(dashboard)/dashboard/providers/[id]/components/ProviderModalsPanel.tsx b/src/app/(dashboard)/dashboard/providers/[id]/components/ProviderModalsPanel.tsx
index 8c7df58b9c..732ff15c19 100644
--- a/src/app/(dashboard)/dashboard/providers/[id]/components/ProviderModalsPanel.tsx
+++ b/src/app/(dashboard)/dashboard/providers/[id]/components/ProviderModalsPanel.tsx
@@ -50,6 +50,7 @@ interface ProviderModalsPanelProps {
   isCommandCode: boolean;
   isUpstreamProxyProvider: boolean;
   subscriptionRisk: boolean;
+  existingConnectionCount?: number;
   // Risk notice
   showRiskNoticeModal: boolean;
   handleConfirmRiskNotice: () => void;
@@ -146,6 +147,7 @@ export default function ProviderModalsPanel({
   isCcCompatible,
   isUpstreamProxyProvider,
   subscriptionRisk,
+  existingConnectionCount,
   showRiskNoticeModal,
   handleConfirmRiskNotice,
   handleCancelRiskNotice,
@@ -280,6 +282,7 @@ export default function ProviderModalsPanel({
           providerName={providerInfo.name}
           providerWebsite={providerInfo.website}
           initialBaseUrl={siliconFlowInitialBaseUrl}
+          existingConnectionCount={existingConnectionCount}
           isCompatible={isCompatible}
           isAnthropic={isAnthropicProtocolCompatible}
           isCcCompatible={isCcCompatible}
diff --git a/src/app/(dashboard)/dashboard/providers/[id]/components/modals/AddApiKeyModal.tsx b/src/app/(dashboard)/dashboard/providers/[id]/components/modals/AddApiKeyModal.tsx
index d46fbd51d2..eaeeef2931 100644
--- a/src/app/(dashboard)/dashboard/providers/[id]/components/modals/AddApiKeyModal.tsx
+++ b/src/app/(dashboard)/dashboard/providers/[id]/components/modals/AddApiKeyModal.tsx
@@ -33,6 +33,7 @@ import { useOpenRouterPresetControl } from "../OpenRouterPresetInput";
 import WebSessionCredentialGuide from "../WebSessionCredentialGuide";
 import CcCompatibleRequestDefaultsFields from "./CcCompatibleRequestDefaultsFields";
 import { buildAddProviderSpecificData } from "./connectionProviderSpecificData";
+import { computeConnectionDefaultName } from "./computeConnectionDefaultName";
 import QuotaScrapingFields, { EMPTY_QUOTA_SCRAPING_FIELDS } from "./QuotaScrapingFields";
 import GlmTeamQuotaFields, { EMPTY_GLM_TEAM_QUOTA_FIELDS } from "./GlmTeamQuotaFields";
 export interface AddApiKeyModalProps {
@@ -41,6 +42,7 @@ export interface AddApiKeyModalProps {
   providerName?: string;
   providerWebsite?: string;
   initialBaseUrl?: string;
+  existingConnectionCount?: number;
   isCompatible?: boolean;
   isAnthropic?: boolean;
   isCcCompatible?: boolean;
@@ -64,6 +66,7 @@ export default function AddApiKeyModal({
   providerName,
   providerWebsite,
   initialBaseUrl,
+  existingConnectionCount = 0,
   isCompatible,
   isAnthropic,
   isCcCompatible,
@@ -114,7 +117,7 @@ export default function AddApiKeyModal({
       }[commandCodeAuthState.phase]
     : null;
   const [formData, setFormData] = useState({
-    name: "main", // #5421: required field; default resists autofill garbage (was "" → "wiw")
+    name: computeConnectionDefaultName(existingConnectionCount),
     apiKey: "",
     tokenSecret: "", // #5446 — Modal Token Secret (joined with apiKey as id:secret)
     defaultModel: "",
@@ -148,11 +151,15 @@ export default function AddApiKeyModal({
     const wasOpen = wasOpenRef.current;
     wasOpenRef.current = isOpen;
     if (!isOpen || wasOpen) return;
+    // On open, reset baseUrl and assign a unique default name so a second API key
+    // for the same provider doesn't reuse "main" and trigger the backend
+    // name-based upsert that would silently overwrite the first connection (#6499).
     setFormData((current) => ({
       ...current,
+      name: computeConnectionDefaultName(existingConnectionCount),
       baseUrl: initialBaseUrl || defaultBaseUrl,
     }));
-  }, [defaultBaseUrl, initialBaseUrl, isOpen]);
+  }, [defaultBaseUrl, initialBaseUrl, isOpen, existingConnectionCount]);
   const bulkSupported = supportsBulkApiKey(provider);
   const [mode, setMode] = useState<"single" | "bulk">("single");
   const [bulkText, setBulkText] = useState("");
diff --git a/src/app/(dashboard)/dashboard/providers/[id]/components/modals/computeConnectionDefaultName.ts b/src/app/(dashboard)/dashboard/providers/[id]/components/modals/computeConnectionDefaultName.ts
new file mode 100644
index 0000000000..7e0bf4cf45
--- /dev/null
+++ b/src/app/(dashboard)/dashboard/providers/[id]/components/modals/computeConnectionDefaultName.ts
@@ -0,0 +1,10 @@
+// #6499 — a fresh API-key connection defaults its name to "main". The backend
+// upserts connections by (provider, name), so opening the modal a second time for
+// the same provider with the same "main" name silently OVERWRITES the first
+// connection. Deriving a unique default from the existing connection count keeps
+// the first connection ("main") backward-compatible while giving each subsequent
+// one a distinct name ("main-2", "main-3", …).
+export function computeConnectionDefaultName(existingConnectionCount?: number): string {
+  const count = existingConnectionCount ?? 0;
+  return count <= 0 ? "main" : `main-${count + 1}`;
+}
diff --git a/tests/unit/compute-connection-default-name-6499.test.ts b/tests/unit/compute-connection-default-name-6499.test.ts
new file mode 100644
index 0000000000..9c0bda08af
--- /dev/null
+++ b/tests/unit/compute-connection-default-name-6499.test.ts
@@ -0,0 +1,27 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import { computeConnectionDefaultName } from "@/app/(dashboard)/dashboard/providers/[id]/components/modals/computeConnectionDefaultName";
+
+// #6499 — the backend upserts API-key connections by (provider, name), so a second
+// connection defaulting to "main" silently overwrites the first. The default name
+// must stay "main" for the first connection (backward compatible) and get a unique
+// numeric suffix afterwards.
+
+test("first connection defaults to 'main'", () => {
+  assert.equal(computeConnectionDefaultName(0), "main");
+});
+
+test("undefined count is treated as zero → 'main'", () => {
+  assert.equal(computeConnectionDefaultName(undefined), "main");
+});
+
+test("subsequent connections get a unique numeric suffix", () => {
+  assert.equal(computeConnectionDefaultName(1), "main-2");
+  assert.equal(computeConnectionDefaultName(2), "main-3");
+  assert.equal(computeConnectionDefaultName(9), "main-10");
+});
+
+test("negative counts are clamped to 'main' (never a broken 'main-0')", () => {
+  assert.equal(computeConnectionDefaultName(-1), "main");
+});