diff --git a/setup/js/create_pull_request.cjs b/setup/js/create_pull_request.cjs
index 313840c..6f41585 100644
--- a/setup/js/create_pull_request.cjs
+++ b/setup/js/create_pull_request.cjs
@@ -33,7 +33,7 @@ const { isStagedMode } = require("./safe_output_helpers.cjs");
 const { normalizeCommitSHA } = require("./commit_sha_helpers.cjs");
 const { withRetry, RATE_LIMIT_RETRY_CONFIG } = require("./error_recovery.cjs");
 const { findAgent, getIssueDetails, assignAgentToIssue } = require("./assign_agent_helpers.cjs");
-const { ensureFullHistoryForBundle, extractBundlePrerequisiteCommits, linearizeRangeAsCommit } = require("./git_helpers.cjs");
+const { ensureFullHistoryForBundle, extractBundlePrerequisiteCommits, isShallowOrSparseCheckout, linearizeRangeAsCommit } = require("./git_helpers.cjs");
 const { parseDiffGitHeader: parseDiffGitHeaderPaths, extractDiffGitHeaderEntries } = require("./patch_path_helpers.cjs");
 const { resolveAllowedMentionsFromPayload } = require("./resolve_mentions_from_payload.cjs");
 const {
@@ -211,7 +211,15 @@ async function applyBundleToBranch(bundleFilePath, branchName, originalAgentBran
         core.warning(`Bundle fetch with ${bundleBranchRef} failed due to ${prerequisiteCommits.length} missing prerequisite commit(s); fetching prerequisites from origin and retrying`);
         core.info(`Prerequisite commits: ${summarizeListForLog(prerequisiteCommits)}`);
         core.info(`Fetching ${prerequisiteCommits.length} prerequisite commit(s) from origin`);
-        await execApi.exec("git", ["fetch", "origin", ...prerequisiteCommits]);
+        // Use --filter=blob:none only when the local repo is already shallow or sparse —
+        // in a full clone we already have all blobs and must not convert the repo to a
+        // partial clone (which would trigger lazy blob fetches on later operations).
+        const useBlobFilter = await isShallowOrSparseCheckout(execApi);
+        const prerequisiteFetchArgs = useBlobFilter ? ["fetch", "--filter=blob:none", "origin", ...prerequisiteCommits] : ["fetch", "origin", ...prerequisiteCommits];
+        if (useBlobFilter) {
+          core.info("Using --filter=blob:none for prerequisite fetch (shallow or sparse checkout detected)");
+        }
+        await execApi.exec("git", prerequisiteFetchArgs);
         core.info("Fetched prerequisite commits from origin successfully");
         try {
           core.info(`Retrying bundle fetch from ${bundleBranchRef} into ${bundleTempRef} after prerequisite recovery`);
diff --git a/setup/js/git_helpers.cjs b/setup/js/git_helpers.cjs
index b6a6c33..d803db2 100644
--- a/setup/js/git_helpers.cjs
+++ b/setup/js/git_helpers.cjs
@@ -180,6 +180,44 @@ async function ensureFullHistoryForBundle(execApi, options = {}) {
   }
 }
 
+/**
+ * Return true when the local repository is shallow OR has sparse-checkout enabled.
+ *
+ * This is the gate for using `--filter=blob:none` on follow-up fetches (e.g. bundle
+ * prerequisite recovery). In a full, non-sparse clone the repo already contains all
+ * blobs for committed history; adding `--filter=blob:none` to a fetch would convert
+ * it to a partial clone and cause subsequent operations to lazily re-fetch blobs.
+ * In shallow or sparse checkouts we already accept partial object availability, so
+ * filtering blobs is consistent and saves bandwidth.
+ *
+ * Both probes are best-effort — on any error we return `false` (do not filter),
+ * which is the safe default that preserves the legacy unfiltered fetch behavior.
+ *
+ * @param {{ getExecOutput: Function }} execApi - Exec API to run git commands.
+ * @param {Object} [options] - Options passed through to exec calls.
+ * @returns {Promise<boolean>}
+ */
+async function isShallowOrSparseCheckout(execApi, options = {}) {
+  const probeOptions = { ...options, ignoreReturnCode: true };
+  try {
+    const { stdout, exitCode } = await execApi.getExecOutput("git", ["rev-parse", "--is-shallow-repository"], probeOptions);
+    if (exitCode === 0 && stdout.trim() === "true") {
+      return true;
+    }
+  } catch {
+    // Fall through to sparse check; if both probes fail, return false (no filter).
+  }
+  try {
+    const { stdout, exitCode } = await execApi.getExecOutput("git", ["config", "--get", "core.sparseCheckout"], probeOptions);
+    if (exitCode === 0 && stdout.trim().toLowerCase() === "true") {
+      return true;
+    }
+  } catch {
+    // Fall through.
+  }
+  return false;
+}
+
 /**
  * Extract prerequisite commit SHAs from git bundle fetch error output.
  *
@@ -265,5 +303,6 @@ module.exports = {
   extractBundlePrerequisiteCommits,
   getGitAuthEnv,
   hasMergeCommitsInRange,
+  isShallowOrSparseCheckout,
   linearizeRangeAsCommit,
 };
diff --git a/setup/js/model_multipliers.json b/setup/js/model_multipliers.json
index fbb31eb..7af7e11 100644
--- a/setup/js/model_multipliers.json
+++ b/setup/js/model_multipliers.json
@@ -37,13 +37,10 @@
     "claude-opus-4.6": 27.0,
     "claude-3-5-opus": 5.0,
     "claude-3-opus": 5.0,
-    "gpt-4o": 0.33,
     "gpt-4o-2024-05-13": 0.33,
     "gpt-4o-2024-08-06": 0.33,
     "gpt-4o-2024-11-20": 0.33,
-    "gpt-4o-mini": 0.33,
     "gpt-4o-mini-2024-07-18": 0.33,
-    "gpt-4.1": 1.0,
     "gpt-4.1-2025-04-14": 1.0,
     "gpt-41-copilot": 1.0,
     "gpt-4.1-mini": 1.0,
@@ -86,7 +83,6 @@
     "gpt-5.4-2026-03-05": 6.0,
     "gpt-5.4-mini": 6.0,
     "gpt-5.4-mini-2026-03-17": 6.0,
-    "gpt-5.4-nano": 6.0,
     "gpt-5.4-nano-2026-03-17": 6.0,
     "gpt-5.4-pro": 6.0,
     "gpt-5.4-pro-2026-03-05": 6.0,
diff --git a/setup/js/push_to_pull_request_branch.cjs b/setup/js/push_to_pull_request_branch.cjs
index dbe627a..20d6fb2 100644
--- a/setup/js/push_to_pull_request_branch.cjs
+++ b/setup/js/push_to_pull_request_branch.cjs
@@ -17,7 +17,7 @@ const { createAuthenticatedGitHubClient } = require("./handler_auth.cjs");
 const { checkFileProtection } = require("./manifest_file_helpers.cjs");
 const { buildWorkflowRunUrl } = require("./workflow_metadata_helpers.cjs");
 const { renderTemplateFromFile, buildProtectedFileList, getPromptPath } = require("./messages_core.cjs");
-const { ensureFullHistoryForBundle, getGitAuthEnv, extractBundlePrerequisiteCommits, linearizeRangeAsCommit } = require("./git_helpers.cjs");
+const { ensureFullHistoryForBundle, getGitAuthEnv, extractBundlePrerequisiteCommits, isShallowOrSparseCheckout, linearizeRangeAsCommit } = require("./git_helpers.cjs");
 const { normalizeCommitSHA } = require("./commit_sha_helpers.cjs");
 const { findRepoCheckout } = require("./find_repo_checkout.cjs");
 const { getThreatDetectedMarker } = require("./threat_detection_warning.cjs");
@@ -742,7 +742,16 @@ async function main(config = {}) {
             if (prerequisiteCommits.length > 0) {
               core.warning(`Bundle fetch failed due to ${prerequisiteCommits.length} missing prerequisite commit(s); fetching prerequisites from origin and retrying`);
               core.info(`Fetching ${prerequisiteCommits.length} prerequisite commit(s) from origin`);
-              await exec.exec("git", ["fetch", "origin", ...prerequisiteCommits], { env: { ...process.env, ...gitAuthEnv }, ...baseGitOpts });
+              // Use --filter=blob:none only when the local repo is already shallow or sparse —
+              // in a full clone we already have all blobs and must not convert the repo to a
+              // partial clone (which would trigger lazy blob fetches on later operations).
+              const prereqGitOpts = { env: { ...process.env, ...gitAuthEnv }, ...baseGitOpts };
+              const useBlobFilter = await isShallowOrSparseCheckout(exec, prereqGitOpts);
+              const prerequisiteFetchArgs = useBlobFilter ? ["fetch", "--filter=blob:none", "origin", ...prerequisiteCommits] : ["fetch", "origin", ...prerequisiteCommits];
+              if (useBlobFilter) {
+                core.info("Using --filter=blob:none for prerequisite fetch (shallow or sparse checkout detected)");
+              }
+              await exec.exec("git", prerequisiteFetchArgs, prereqGitOpts);
               core.info("Fetched prerequisite commits from origin successfully");
               await exec.exec("git", ["fetch", bundleFilePath, bundleFetchRef], baseGitOpts);
               core.info("Bundle fetch retry succeeded after prerequisite recovery");
diff --git a/setup/sh/install_antigravity_cli.sh b/setup/sh/install_antigravity_cli.sh
index 3d5769a..858ffbb 100644
--- a/setup/sh/install_antigravity_cli.sh
+++ b/setup/sh/install_antigravity_cli.sh
@@ -13,6 +13,7 @@ set +o histexpand
 # Security features:
 #   - Downloads binary directly from Google Cloud Storage over HTTPS
 #   - Verifies SHA256 checksum against official checksums.txt before installation
+#   - Warns and skips checksum verification if checksums.txt is unavailable (HTTP 404)
 #   - Fails fast if checksum verification fails
 #   - Fails fast on any curl errors
 
@@ -74,34 +75,51 @@ sha256_hash() {
 TEMP_DIR=$(mktemp -d)
 trap 'rm -rf "$TEMP_DIR"' EXIT
 
-# Download checksums file from GCS
+# Download checksums file from GCS (if available for this version)
 echo "Downloading checksums from ${CHECKSUMS_URL}..."
-curl -fsSL --retry 3 --retry-delay 5 -o "${TEMP_DIR}/checksums.txt" "${CHECKSUMS_URL}"
+if ! CHECKSUMS_DOWNLOAD_STATUS=$(curl -sSL --retry 3 --retry-delay 5 -w "%{http_code}" -o "${TEMP_DIR}/checksums.txt" "${CHECKSUMS_URL}"); then
+  echo "ERROR: Failed to download checksums.txt due to a network or TLS error"
+  exit 1
+fi
+
+VERIFY_CHECKSUM=true
+if [ "${CHECKSUMS_DOWNLOAD_STATUS}" = "404" ]; then
+  echo "WARNING: checksums.txt not found for version ${VERSION}; skipping checksum verification."
+  rm -f "${TEMP_DIR}/checksums.txt"
+  VERIFY_CHECKSUM=false
+elif [ "${CHECKSUMS_DOWNLOAD_STATUS}" != "200" ]; then
+  echo "ERROR: Failed to download checksums.txt (HTTP ${CHECKSUMS_DOWNLOAD_STATUS})"
+  exit 1
+fi
 
 # Download binary tarball from GCS over HTTPS
 echo "Downloading from ${TARBALL_URL}..."
 curl -fsSL --retry 3 --retry-delay 5 -o "${TEMP_DIR}/${TARBALL_NAME}" "${TARBALL_URL}"
 
-# Verify SHA256 checksum before extracting
-echo "Verifying SHA256 checksum for ${TARBALL_NAME}..."
-EXPECTED_CHECKSUM=$(awk -v fname="${TARBALL_NAME}" '$2 == fname {print $1; exit}' "${TEMP_DIR}/checksums.txt" | tr 'A-F' 'a-f')
+# Verify SHA256 checksum before extracting (when checksums.txt is available)
+if [ "${VERIFY_CHECKSUM}" = "true" ]; then
+  echo "Verifying SHA256 checksum for ${TARBALL_NAME}..."
+  EXPECTED_CHECKSUM=$(awk -v fname="${TARBALL_NAME}" '$2 == fname {print $1; exit}' "${TEMP_DIR}/checksums.txt" | tr 'A-F' 'a-f')
 
-if [ -z "$EXPECTED_CHECKSUM" ]; then
-  echo "ERROR: Could not find checksum for ${TARBALL_NAME} in checksums.txt"
-  exit 1
-fi
+  if [ -z "$EXPECTED_CHECKSUM" ]; then
+    echo "ERROR: Could not find checksum for ${TARBALL_NAME} in checksums.txt"
+    exit 1
+  fi
 
-ACTUAL_CHECKSUM=$(sha256_hash "${TEMP_DIR}/${TARBALL_NAME}" | tr 'A-F' 'a-f')
+  ACTUAL_CHECKSUM=$(sha256_hash "${TEMP_DIR}/${TARBALL_NAME}" | tr 'A-F' 'a-f')
 
-if [ "$EXPECTED_CHECKSUM" != "$ACTUAL_CHECKSUM" ]; then
-  echo "ERROR: Checksum verification failed!"
-  echo "  Expected: $EXPECTED_CHECKSUM"
-  echo "  Got:      $ACTUAL_CHECKSUM"
-  echo "  The downloaded file may be corrupted or tampered with"
-  exit 1
-fi
+  if [ "$EXPECTED_CHECKSUM" != "$ACTUAL_CHECKSUM" ]; then
+    echo "ERROR: Checksum verification failed!"
+    echo "  Expected: $EXPECTED_CHECKSUM"
+    echo "  Got:      $ACTUAL_CHECKSUM"
+    echo "  The downloaded file may be corrupted or tampered with"
+    exit 1
+  fi
 
-echo "✓ Checksum verification passed for ${TARBALL_NAME}"
+  echo "✓ Checksum verification passed for ${TARBALL_NAME}"
+else
+  echo "WARNING: Proceeding without checksum verification for ${TARBALL_NAME}"
+fi
 
 # Extract and install binary
 echo "Installing binary to ${INSTALL_DIR}/${BINARY_NAME}..."