diff --git a/open-sse/services/usage.ts b/open-sse/services/usage.ts
index f18ba970bc..e96eeaa123 100644
--- a/open-sse/services/usage.ts
+++ b/open-sse/services/usage.ts
@@ -3,14 +3,6 @@
  */
 
 import { PROVIDERS } from "../config/constants.ts";
-
-// Quota / usage upstream URLs (overridable for testing or relays).
-const CROF_USAGE_URL = process.env.OMNIROUTE_CROF_USAGE_URL ?? "https://crof.ai/usage_api/";
-const GEMINI_CLI_USAGE_URL =
-  process.env.OMNIROUTE_GEMINI_CLI_USAGE_URL ??
-  "https://cloudcode-pa.googleapis.com/v1internal:loadCodeAssist";
-const CODEWHISPERER_BASE_URL =
-  process.env.OMNIROUTE_CODEWHISPERER_BASE_URL ?? "https://codewhisperer.us-east-1.amazonaws.com";
 import {
   getAntigravityFetchAvailableModelsUrls,
   ANTIGRAVITY_BASE_URLS,
@@ -43,6 +35,14 @@ import {
   extractCodeAssistSubscriptionTier,
 } from "./codeAssistSubscription.ts";
 
+// Quota / usage upstream URLs (overridable for testing or relays).
+const CROF_USAGE_URL = process.env.OMNIROUTE_CROF_USAGE_URL ?? "https://crof.ai/usage_api/";
+const GEMINI_CLI_USAGE_URL =
+  process.env.OMNIROUTE_GEMINI_CLI_USAGE_URL ??
+  "https://cloudcode-pa.googleapis.com/v1internal:loadCodeAssist";
+const CODEWHISPERER_BASE_URL =
+  process.env.OMNIROUTE_CODEWHISPERER_BASE_URL ?? "https://codewhisperer.us-east-1.amazonaws.com";
+
 // Antigravity API config (credentials from PROVIDERS via credential loader)
 const ANTIGRAVITY_CONFIG = {
   quotaApiUrls: getAntigravityFetchAvailableModelsUrls(),
@@ -1940,8 +1940,9 @@ async function getAntigravityUsage(
 
       const rawFraction = toNumber(quotaInfo.remainingFraction, -1);
       const resetAt = parseResetTime(quotaInfo.resetTime);
-      // Default to 100% when the API doesn't report a fraction
-      const remainingFraction = rawFraction < 0 ? 1 : rawFraction;
+      // When remainingFraction is undefined/NaN (exhausted quota), default to 0%. Clamp to valid range [0, 1]
+      // Unlimited models have remainingFraction=1 AND no resetTime
+      const remainingFraction = rawFraction < 0 ? 0 : Math.max(0, Math.min(1, rawFraction));
       // Models with no resetTime and full remaining are unlimited (e.g. tab-completion models)
       const isUnlimited = !resetAt && remainingFraction >= 1;
       const remainingPercentage = remainingFraction * 100;
diff --git a/src/lib/usage/fetcher.ts b/src/lib/usage/fetcher.ts
index 58f4d3d086..092de749d7 100644
--- a/src/lib/usage/fetcher.ts
+++ b/src/lib/usage/fetcher.ts
@@ -348,9 +348,13 @@ async function getAntigravityUsage(
       if (info.isInternal) continue;
       const quotaInfo = (info.quotaInfo as Record<string, unknown>) ?? {};
 
-      if ("remainingFraction" in quotaInfo) {
+      // Process models with any quota metadata (exhausted models may have only resetTime, active models have remainingFraction, credit-based models have empty quotaInfo)
+      if (Object.keys(quotaInfo).length > 0) {
+        // Default to 0 when remainingFraction is undefined/null/invalid, clamp to valid range [0, 1]
         const fraction =
-          typeof quotaInfo.remainingFraction === "number" ? quotaInfo.remainingFraction : 1;
+          typeof quotaInfo.remainingFraction === "number"
+            ? Math.max(0, Math.min(1, quotaInfo.remainingFraction))
+            : 0;
         const resetTime = typeof quotaInfo.resetTime === "string" ? quotaInfo.resetTime : null;
         modelQuotas[modelId] = {
           remaining: Math.round(fraction * 100),
@@ -360,7 +364,7 @@ async function getAntigravityUsage(
         quotaModelsTotal++;
         if (fraction > 0) quotaModelsAvailable++;
       }
-      // Credit-based models have no remainingFraction — their availability is
+      // Credit-based models have empty quotaInfo — their availability is
       // tracked via the GOOGLE_ONE_AI credit balance cached from SSE responses.
     }
 
diff --git a/tests/unit/antigravity-usage-fetcher.test.ts b/tests/unit/antigravity-usage-fetcher.test.ts
new file mode 100644
index 0000000000..b53e482d53
--- /dev/null
+++ b/tests/unit/antigravity-usage-fetcher.test.ts
@@ -0,0 +1,285 @@
+/**
+ * Tests for src/lib/usage/fetcher.ts — Antigravity quota parsing.
+ *
+ * Verifies that remainingFraction is correctly parsed:
+ * - undefined → 0% remaining (exhausted quota)
+ * - 0 → 0% remaining (exhausted quota, explicit)
+ * - 1.0 → 100% remaining (full quota)
+ * - 0.5 → 50% remaining (partial quota)
+ */
+
+import { describe, it, mock } from "node:test";
+import assert from "node:assert/strict";
+
+describe("getUsageForProvider (antigravity in fetcher.ts)", () => {
+  const connectionBase = {
+    provider: "antigravity",
+    accessToken: "fake-token",
+    providerSpecificData: {},
+    projectId: undefined,
+    id: "test-conn",
+  };
+
+  it("defaults to 0% remaining when remainingFraction is undefined", async () => {
+    const fetcherModule = await import("../../src/lib/usage/fetcher.ts");
+    const { getUsageForProvider } = fetcherModule;
+
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-2.5-pro": {
+            quotaInfo: {
+              remainingFraction: undefined,
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const result = await getUsageForProvider(connectionBase);
+      assert.ok(result, "should return a result");
+
+      if ("modelQuotas" in result) {
+        const quota = result.modelQuotas["gemini-2.5-pro"];
+        assert.ok(quota, "should have quota for gemini-2.5-pro");
+        assert.equal(quota.remaining, 0, "remaining should be 0%");
+        assert.equal(quota.limited, true, "should be marked as limited");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("defaults to 0% remaining when remainingFraction key is absent (exhausted quota)", async () => {
+    const fetcherModule = await import("../../src/lib/usage/fetcher.ts");
+    const { getUsageForProvider } = fetcherModule;
+
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-2.5-pro": {
+            quotaInfo: {
+              // remainingFraction key is omitted (exhausted quota)
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const result = await getUsageForProvider(connectionBase);
+      assert.ok(result, "should return a result");
+
+      if ("modelQuotas" in result) {
+        const quota = result.modelQuotas["gemini-2.5-pro"];
+        assert.ok(quota, "should have quota for gemini-2.5-pro");
+        assert.equal(quota.remaining, 0, "remaining should be 0% when key is absent");
+        assert.equal(quota.limited, true, "should be marked as limited");
+        assert.equal(quota.resetAt, "2026-05-26T00:00:00Z", "should preserve resetTime");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("parses remainingFraction=0 as exhausted quota", async () => {
+    const fetcherModule = await import("../../src/lib/usage/fetcher.ts");
+    const { getUsageForProvider } = fetcherModule;
+
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-2.5-pro": {
+            quotaInfo: {
+              remainingFraction: 0,
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const result = await getUsageForProvider(connectionBase);
+      assert.ok(result, "should return a result");
+
+      if ("modelQuotas" in result) {
+        const quota = result.modelQuotas["gemini-2.5-pro"];
+        assert.ok(quota, "should have quota for gemini-2.5-pro");
+        assert.equal(quota.remaining, 0, "remaining should be 0%");
+        assert.equal(quota.limited, true, "should be marked as limited");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("parses remainingFraction=1.0 with resetTime as full quota", async () => {
+    const fetcherModule = await import("../../src/lib/usage/fetcher.ts");
+    const { getUsageForProvider } = fetcherModule;
+
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-2.5-pro": {
+            quotaInfo: {
+              remainingFraction: 1.0,
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const result = await getUsageForProvider(connectionBase);
+      assert.ok(result, "should return a result");
+
+      if ("modelQuotas" in result) {
+        const quota = result.modelQuotas["gemini-2.5-pro"];
+        assert.ok(quota, "should have quota for gemini-2.5-pro");
+        assert.equal(quota.remaining, 100, "remaining should be 100%");
+        assert.equal(quota.limited, false, "should not be marked as limited");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("parses remainingFraction=0.5 as partial quota", async () => {
+    const fetcherModule = await import("../../src/lib/usage/fetcher.ts");
+    const { getUsageForProvider } = fetcherModule;
+
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-2.5-pro": {
+            quotaInfo: {
+              remainingFraction: 0.5,
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const result = await getUsageForProvider(connectionBase);
+      assert.ok(result, "should return a result");
+
+      if ("modelQuotas" in result) {
+        const quota = result.modelQuotas["gemini-2.5-pro"];
+        assert.ok(quota, "should have quota for gemini-2.5-pro");
+        assert.equal(quota.remaining, 50, "remaining should be 50%");
+        assert.equal(quota.limited, false, "should not be marked as limited");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("skips credit-based models without remainingFraction", async () => {
+    const fetcherModule = await import("../../src/lib/usage/fetcher.ts");
+    const { getUsageForProvider } = fetcherModule;
+
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-2.5-pro": {
+            quotaInfo: {},
+          },
+        },
+      }),
+    }));
+
+    try {
+      const result = await getUsageForProvider(connectionBase);
+      assert.ok(result, "should return a result");
+
+      if ("modelQuotas" in result) {
+        assert.equal(
+          Object.keys(result.modelQuotas).length,
+          0,
+          "should not include credit-based models"
+        );
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("clamps remainingFraction > 1 to 100%", async () => {
+    const fetcherModule = await import("../../src/lib/usage/fetcher.ts");
+    const { getUsageForProvider } = fetcherModule;
+
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-2.5-pro": {
+            quotaInfo: {
+              remainingFraction: 1.5,
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const result = await getUsageForProvider(connectionBase);
+      assert.ok(result, "should return a result");
+
+      if ("modelQuotas" in result) {
+        const quota = result.modelQuotas["gemini-2.5-pro"];
+        assert.ok(quota, "should have quota for gemini-2.5-pro");
+        assert.equal(quota.remaining, 100, "remaining should be clamped to 100%");
+        assert.equal(quota.limited, false, "should not be marked as limited");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("clamps negative remainingFraction to 0%", async () => {
+    const fetcherModule = await import("../../src/lib/usage/fetcher.ts");
+    const { getUsageForProvider } = fetcherModule;
+
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-2.5-pro": {
+            quotaInfo: {
+              remainingFraction: -0.5,
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const result = await getUsageForProvider(connectionBase);
+      assert.ok(result, "should return a result");
+
+      if ("modelQuotas" in result) {
+        const quota = result.modelQuotas["gemini-2.5-pro"];
+        assert.ok(quota, "should have quota for gemini-2.5-pro");
+        assert.equal(quota.remaining, 0, "remaining should be clamped to 0%");
+        assert.equal(quota.limited, true, "should be marked as limited");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+});
diff --git a/tests/unit/antigravity-usage-service.test.ts b/tests/unit/antigravity-usage-service.test.ts
new file mode 100644
index 0000000000..9a357f6a01
--- /dev/null
+++ b/tests/unit/antigravity-usage-service.test.ts
@@ -0,0 +1,261 @@
+/**
+ * Tests for open-sse/services/usage.ts — Antigravity quota parsing.
+ *
+ * Verifies that remainingFraction is correctly parsed:
+ * - undefined → 0% remaining (exhausted quota)
+ * - 0 → 0% remaining (exhausted quota, explicit)
+ * - 1.0 → 100% remaining (full quota)
+ * - 1.0 without resetTime → unlimited (e.g. tab-completion)
+ * - 0.5 → 50% remaining (partial quota)
+ */
+
+import { describe, it, mock } from "node:test";
+import assert from "node:assert/strict";
+
+describe("getUsageForProvider (antigravity in usage.ts)", () => {
+  const connectionBase = {
+    id: "test-conn",
+    provider: "antigravity",
+    accessToken: "fake-token",
+    providerSpecificData: {},
+    projectId: undefined,
+  };
+
+  it("defaults to 0% remaining when remainingFraction is undefined", async () => {
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-3.5-flash-preview": {
+            quotaInfo: {
+              remainingFraction: undefined,
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const usageModule = await import("../../open-sse/services/usage.ts");
+      const { getUsageForProvider } = usageModule;
+
+      const result = await getUsageForProvider(connectionBase, { forceRefresh: true });
+      assert.ok(result, "should return a result");
+      assert.ok("quotas" in result, "should have quotas");
+
+      if ("quotas" in result) {
+        const quota = result.quotas["gemini-3.5-flash-preview"];
+        assert.ok(quota, "should have quota for gemini-3.5-flash-preview");
+        assert.equal(quota.remainingPercentage, 0, "remaining should be 0%");
+        assert.equal(quota.unlimited, false, "should not be unlimited");
+        assert.equal(quota.used > 0, true, "used should be > 0 when quota is exhausted");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("parses remainingFraction=0 as exhausted quota", async () => {
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-3.5-flash-preview": {
+            quotaInfo: {
+              remainingFraction: 0,
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const usageModule = await import("../../open-sse/services/usage.ts");
+      const { getUsageForProvider } = usageModule;
+
+      const result = await getUsageForProvider(connectionBase, { forceRefresh: true });
+      assert.ok(result, "should return a result");
+      assert.ok("quotas" in result, "should have quotas");
+
+      if ("quotas" in result) {
+        const quota = result.quotas["gemini-3.5-flash-preview"];
+        assert.ok(quota, "should have quota for gemini-3.5-flash-preview");
+        assert.equal(quota.remainingPercentage, 0, "remaining should be 0%");
+        assert.equal(quota.unlimited, false, "should not be unlimited");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("parses remainingFraction=1.0 with resetTime as full quota", async () => {
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-3.5-flash-preview": {
+            quotaInfo: {
+              remainingFraction: 1.0,
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const usageModule = await import("../../open-sse/services/usage.ts");
+      const { getUsageForProvider } = usageModule;
+
+      const result = await getUsageForProvider(connectionBase, { forceRefresh: true });
+      assert.ok(result, "should return a result");
+      assert.ok("quotas" in result, "should have quotas");
+
+      if ("quotas" in result) {
+        const quota = result.quotas["gemini-3.5-flash-preview"];
+        assert.ok(quota, "should have quota for gemini-3.5-flash-preview");
+        assert.equal(quota.remainingPercentage, 100, "remaining should be 100%");
+        assert.equal(quota.unlimited, false, "should not be unlimited (has resetTime)");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("parses remainingFraction=1.0 without resetTime as unlimited (e.g. tab-completion)", async () => {
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-3.1-flash-lite": {
+            quotaInfo: {
+              remainingFraction: 1.0,
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const usageModule = await import("../../open-sse/services/usage.ts");
+      const { getUsageForProvider } = usageModule;
+
+      const result = await getUsageForProvider(connectionBase, { forceRefresh: true });
+      assert.ok(result, "should return a result");
+      assert.ok("quotas" in result, "should have quotas");
+
+      if ("quotas" in result) {
+        const quota = result.quotas["gemini-3.1-flash-lite"];
+        assert.ok(quota, "should have quota for gemini-3.1-flash-lite");
+        assert.equal(quota.remainingPercentage, 100, "remaining should be 100%");
+        assert.equal(quota.unlimited, true, "should be unlimited (no resetTime)");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("parses remainingFraction=0.5 as partial quota", async () => {
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-3.5-flash-preview": {
+            quotaInfo: {
+              remainingFraction: 0.5,
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const usageModule = await import("../../open-sse/services/usage.ts");
+      const { getUsageForProvider } = usageModule;
+
+      const result = await getUsageForProvider(connectionBase, { forceRefresh: true });
+      assert.ok(result, "should return a result");
+      assert.ok("quotas" in result, "should have quotas");
+
+      if ("quotas" in result) {
+        const quota = result.quotas["gemini-3.5-flash-preview"];
+        assert.ok(quota, "should have quota for gemini-3.5-flash-preview");
+        assert.equal(quota.remainingPercentage, 50, "remaining should be 50%");
+        assert.equal(quota.unlimited, false, "should not be unlimited");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("clamps remainingFraction > 1 to 100%", async () => {
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-3.5-flash-preview": {
+            quotaInfo: {
+              remainingFraction: 1.5,
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const usageModule = await import("../../open-sse/services/usage.ts");
+      const { getUsageForProvider } = usageModule;
+
+      const result = await getUsageForProvider(connectionBase, { forceRefresh: true });
+      assert.ok(result, "should return a result");
+      assert.ok("quotas" in result, "should have quotas");
+
+      if ("quotas" in result) {
+        const quota = result.quotas["gemini-3.5-flash-preview"];
+        assert.ok(quota, "should have quota for gemini-3.5-flash-preview");
+        assert.equal(quota.remainingPercentage, 100, "remaining should be clamped to 100%");
+        assert.equal(quota.unlimited, false, "should not be unlimited (has resetTime)");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+
+  it("clamps negative remainingFraction to 0%", async () => {
+    const mockFetch = mock.method(global, "fetch", async () => ({
+      ok: true,
+      json: async () => ({
+        models: {
+          "gemini-3.5-flash-preview": {
+            quotaInfo: {
+              remainingFraction: -0.5,
+              resetTime: "2026-05-26T00:00:00Z",
+            },
+          },
+        },
+      }),
+    }));
+
+    try {
+      const usageModule = await import("../../open-sse/services/usage.ts");
+      const { getUsageForProvider } = usageModule;
+
+      const result = await getUsageForProvider(connectionBase, { forceRefresh: true });
+      assert.ok(result, "should return a result");
+      assert.ok("quotas" in result, "should have quotas");
+
+      if ("quotas" in result) {
+        const quota = result.quotas["gemini-3.5-flash-preview"];
+        assert.ok(quota, "should have quota for gemini-3.5-flash-preview");
+        assert.equal(quota.remainingPercentage, 0, "remaining should be clamped to 0%");
+        assert.equal(quota.unlimited, false, "should not be unlimited");
+      }
+    } finally {
+      mockFetch.mock.restore();
+    }
+  });
+});