diff --git a/.github/config/hive/clients.yaml b/.github/config/hive/clients.yaml
new file mode 100644
index 00000000..46e8af76
--- /dev/null
+++ b/.github/config/hive/clients.yaml
@@ -0,0 +1,4 @@
+- client: ethlambda
+  nametag: devnet4
+- client: ethlambda
+  nametag: devnet5
diff --git a/.github/scripts/check-hive-results.sh b/.github/scripts/check-hive-results.sh
new file mode 100644
index 00000000..d1cb3e21
--- /dev/null
+++ b/.github/scripts/check-hive-results.sh
@@ -0,0 +1,82 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+results_dir="${1:-src/results}"
+
+if ! command -v jq >/dev/null 2>&1; then
+  echo "jq is required to parse Hive results but was not found in PATH"
+  exit 1
+fi
+
+if [ ! -d "${results_dir}" ]; then
+  echo "Hive results directory '${results_dir}' not found"
+  exit 1
+fi
+
+shopt -s nullglob
+json_files=("${results_dir}"/*.json)
+shopt -u nullglob
+
+if [ "${#json_files[@]}" -eq 0 ]; then
+  echo "No Hive JSON result files found in ${results_dir}"
+  exit 1
+fi
+
+failures=0
+failed_logs_root="${results_dir}/failed_logs"
+rm -rf "${failed_logs_root}"
+mkdir -p "${failed_logs_root}"
+
+for json_file in "${json_files[@]}"; do
+  if [[ "${json_file}" == *"hive.json" ]]; then
+    continue
+  fi
+
+  suite_name="$(jq -r '.name // empty' "${json_file}")"
+  suite_label="${suite_name:-$(basename "${json_file}" .json)}"
+  failed_cases="$(jq '[.testCases[]? | select(.summaryResult.pass != true)] | length' "${json_file}")"
+
+  if [ "${failed_cases}" -eq 0 ]; then
+    continue
+  fi
+
+  failures=$((failures + failed_cases))
+  echo "Detected ${failed_cases} failing Hive test case(s) in ${suite_label}"
+
+  failure_list="$(
+    jq -r '
+      .testCases[]?
+      | select(.summaryResult.pass != true)
+      | . as $case
+      | ($case.summaryResult // {}) as $summary
+      | ($summary.message // $summary.reason // $summary.error // "") as $message
+      | "- " + ($case.name // "unknown test")
+        + (if $message != "" then ": " + $message else "" end)
+    ' "${json_file}"
+  )"
+
+  printf '%s\n' "${failure_list}"
+
+  suite_slug="$(printf '%s' "${suite_label}" | tr '[:upper:]' '[:lower:]' | sed -E 's/[^a-z0-9._-]+/-/g; s/^-//; s/-$//')"
+  suite_dir="${failed_logs_root}/${suite_slug:-suite}"
+  mkdir -p "${suite_dir}"
+
+  cp "${json_file}" "${suite_dir}/"
+  printf '%s\n\n%s\n' "Detected ${failed_cases} failing Hive test case(s) in ${suite_label}" "${failure_list}" > "${suite_dir}/failed-tests.txt"
+
+  if [ -n "${GITHUB_STEP_SUMMARY:-}" ]; then
+    {
+      echo "### Hive failures: ${suite_label}"
+      printf '%s\n' "${failure_list}"
+      echo
+    } >> "${GITHUB_STEP_SUMMARY}"
+  fi
+done
+
+if [ "${failures}" -gt 0 ]; then
+  echo "Hive reported ${failures} failing test case(s) in total"
+  exit 1
+fi
+
+echo "Hive reported no failing test cases."
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c472fd7e..a6fc85bf 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -72,5 +72,212 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
-      - name: Run fixture-based tests
-        uses: ./.github/actions/run-fixture-tests
+      - name: Get leanSpec fixtures release info
+        id: fixtures-release
+        run: |
+          api_url="https://api.github.com/repos/leanEthereum/leanSpec/releases/latest"
+          json=$(curl -sL "$api_url")
+            fixtures_url=$(echo "$json" | python3 -c "import sys,json; j=json.load(sys.stdin); print(next(a.get('browser_download_url') for a in j.get('assets',[]) if a.get('name')=='fixtures-prod-scheme.tar.gz'))")
+            sha_url=$(echo "$json" | python3 -c "import sys,json; j=json.load(sys.stdin); print(next(a.get('browser_download_url') for a in j.get('assets',[]) if a.get('name')=='fixtures-prod-scheme.tar.gz.sha256'))")
+          sha=$(curl -sL "$sha_url" | cut -d' ' -f1)
+          {
+            echo "url=$fixtures_url"
+            echo "sha_url=$sha_url"
+            echo "sha=$sha"
+          } >> $GITHUB_OUTPUT
+
+      - name: Restore test fixtures cache
+        id: cache-fixtures
+        uses: actions/cache/restore@v5
+        with:
+          path: leanSpec/fixtures
+          key: leanspec-fixtures-${{ steps.fixtures-release.outputs.sha }}
+
+      - name: Download leanSpec fixtures release
+        id: download-fixtures
+        if: steps.cache-fixtures.outputs.cache-hit != 'true'
+        run: |
+          tmpdir=$(mktemp -d)
+          trap 'rm -rf "$tmpdir"' EXIT
+          fixtures_url="${{ steps.fixtures-release.outputs.url }}"
+          sha_url="${{ steps.fixtures-release.outputs.sha_url }}"
+          echo "Downloading fixtures from $fixtures_url"
+          curl -L -f -o "$tmpdir/fixtures-prod-scheme.tar.gz" "$fixtures_url"
+          curl -L -f -o "$tmpdir/fixtures-prod-scheme.tar.gz.sha256" "$sha_url"
+          expected=$(cut -d' ' -f1 "$tmpdir/fixtures-prod-scheme.tar.gz.sha256")
+          actual=$(sha256sum "$tmpdir/fixtures-prod-scheme.tar.gz" | awk '{print $1}')
+          if [ "$expected" != "$actual" ]; then
+            echo "SHA256 mismatch: expected $expected, got $actual"
+            exit 1
+          fi
+          rm -rf leanSpec/fixtures
+          mkdir -p leanSpec/fixtures
+          tar -xzf "$tmpdir/fixtures-prod-scheme.tar.gz" -C leanSpec/fixtures --strip-components=1
+
+      # Save fixtures only when the download actually SUCCEEDED, so a
+      # cancelled or failed download never persists a partial fixture set,
+      # while still saving even if the later Rust test step fails.
+      - name: Save test fixtures cache
+        if: >-
+          always()
+          && steps.cache-fixtures.outputs.cache-hit != 'true'
+          && steps.download-fixtures.outcome == 'success'
+        uses: actions/cache/save@v5
+        with:
+          path: leanSpec/fixtures
+          key: ${{ steps.cache-fixtures.outputs.cache-primary-key }}
+
+      # Ensure make sees fixtures as up-to-date (its timestamp must be
+      # newer than leanSpec/, which intermediate steps may have modified).
+      - name: Mark fixtures as up-to-date
+        run: touch leanSpec/fixtures
+
+      - name: Setup Rust
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.92.0"
+
+      - name: Setup cache
+        uses: Swatinem/rust-cache@v2
+
+      - name: Run tests
+        run: make test
+
+  docker_build:
+    name: Build Docker
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Build ethlambda Docker image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: ./Dockerfile
+          build-args: |
+            GIT_COMMIT=${{ github.sha }}
+            GIT_BRANCH=${{ github.ref_name }}
+          push: false
+          tags: |
+            ghcr.io/lambdaclass/ethlambda:devnet4
+            ghcr.io/lambdaclass/ethlambda:devnet5
+          outputs: type=docker,dest=/tmp/ethlambda_image.tar
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
+      - name: Upload image artifacts
+        uses: actions/upload-artifact@v7
+        with:
+          name: ethlambda_image
+          path: /tmp/ethlambda_image.tar
+
+  run-hive:
+    name: Hive - ${{ matrix.name }}
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    needs: docker_build
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - name: "Lean RPC Compat"
+            limit: "rpc-compat"
+            artifact_prefix: lean_rpc_compat
+          - name: "Lean Sync"
+            limit: "sync"
+            artifact_prefix: lean_sync
+          - name: "Lean Client Interop"
+            limit: "client-interop"
+            artifact_prefix: lean_client_interop
+          - name: "Lean Validation"
+            limit: "validation"
+            artifact_prefix: lean_validation
+          - name: "Lean Gossip"
+            limit: "gossip"
+            artifact_prefix: lean_gossip
+          - name: "Lean ReqResp"
+            limit: "reqresp"
+            artifact_prefix: lean_reqresp
+          - name: "Lean Fork Choice Spec Tests"
+            limit: "lean-spec-tests-fork-choice"
+            artifact_prefix: lean_spec_fork_choice
+          - name: "Lean State Transition Spec Tests"
+            limit: "lean-spec-tests-state-transition"
+            artifact_prefix: lean_spec_state_transition
+          - name: "Lean Verify Signatures Spec Tests"
+            limit: "lean-spec-tests-verify-signatures"
+            artifact_prefix: lean_spec_verify_signatures
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Download ethlambda image artifact
+        uses: actions/download-artifact@v6
+        with:
+          name: ethlambda_image
+          path: /tmp
+
+      - name: Load image
+        run: docker load --input /tmp/ethlambda_image.tar
+
+      - name: Load hive client config
+        id: client-config
+        shell: bash
+        run: |
+          {
+            echo "config<<EOF"
+            cat .github/config/hive/clients.yaml
+            echo "EOF"
+          } >> "$GITHUB_OUTPUT"
+
+      - name: Determine hive flags
+        id: hive-flags
+        shell: bash
+        env:
+          SIM_LIMIT: ${{ matrix.limit }}
+        run: |
+          FLAGS="--sim.parallelism 4 --sim.loglevel 3"
+          if [[ -n "$SIM_LIMIT" ]]; then
+            escaped_limit=${SIM_LIMIT//\'/\'\\\'\'}
+            FLAGS+=" --sim.limit '$escaped_limit'"
+          fi
+          echo "flags=$FLAGS" >> "$GITHUB_OUTPUT"
+
+      - name: Run Hive Simulation
+        uses: ethpandaops/hive-github-action@09050fc75bae8a10b1876a0826ca4114ea9ed6e8 # v0.6.3
+        with:
+          hive_repository: ethereum/hive
+          hive_version: dde4f59d04ff0ff8b6585670b08cea1b6c8ab65c
+          simulator: lean
+          client: ethlambda_devnet4
+          client_config: ${{ steps.client-config.outputs.config }}
+          extra_flags: ${{ steps.hive-flags.outputs.flags }}
+
+      - name: Check Hive Results For Failures
+        id: verify-hive-results
+        if: ${{ success() }}
+        shell: bash
+        run: bash ./.github/scripts/check-hive-results.sh src/results
+
+      - name: Upload Hive Failure Logs
+        if: ${{ failure() && steps.verify-hive-results.conclusion == 'failure' }}
+        uses: actions/upload-artifact@v7
+        with:
+          name: hive_failed_logs_${{ matrix.artifact_prefix }}
+          path: src/results/failed_logs
+          if-no-files-found: warn
+
+      - name: Upload Hive Run Artifacts
+        if: ${{ failure() }}
+        uses: actions/upload-artifact@v7
+        with:
+          name: hive_run_artifacts_${{ matrix.artifact_prefix }}
+          path: |
+            src/hive.log
+            src/results
+          if-no-files-found: warn