diff --git a/.github/actions/build-fixtures/action.yaml b/.github/actions/build-fixtures/action.yaml
index 36fff598e02..98148e97246 100644
--- a/.github/actions/build-fixtures/action.yaml
+++ b/.github/actions/build-fixtures/action.yaml
@@ -25,6 +25,9 @@ inputs:
   evm_ref:
     description: "Override the t8n tool branch / tag / commit"
     default: ""
+  upload:
+    description: "Upload the filled fixtures. Set to false to rehearse a fill and discard its output."
+    default: "true"
 runs:
   using: "composite"
   steps:
@@ -77,11 +80,12 @@ runs:
           exit "$EXIT_CODE"
         fi
     - uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0
+      if: inputs.upload == 'true'
       with:
         name: fixtures_${{ inputs.release_name }}
         path: fixtures_${{ inputs.release_name }}.tar.gz
     - name: Upload fixture directory (split)
-      if: inputs.split_label != ''
+      if: inputs.upload == 'true' && inputs.split_label != ''
       uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0
       with:
         name: fixtures__${{ inputs.split_label }}
diff --git a/.github/configs/feature.yaml b/.github/configs/feature.yaml
index 7fca18fd9ef..ba528347f43 100644
--- a/.github/configs/feature.yaml
+++ b/.github/configs/feature.yaml
@@ -1,8 +1,3 @@
-# Unless filling for special features, all features should fill for previous forks (starting from Frontier) too
-mainnet:
-  evm-type: eels
-  fill-params: --until=BPO4 --generate-all-formats
-
 monad:
   evm-type: eels
   fill-params: -m blockchain_test --from=MONAD_EIGHT --until=MONAD_TEN --chain-id=143 -k "not invalid_header"
diff --git a/.github/scripts/check_release_matrix.py b/.github/scripts/check_release_matrix.py
new file mode 100755
index 00000000000..556d5b92bf7
--- /dev/null
+++ b/.github/scripts/check_release_matrix.py
@@ -0,0 +1,124 @@
+#!/usr/bin/env -S uv run --script
+#
+# /// script
+# requires-python = ">=3.12"
+# dependencies = [
+#     "pyyaml",
+# ]
+# ///
+"""
+Build the job matrix for a fixture release rehearsal.
+
+Usage: `check_release_matrix.py [features] [branch]`, where `features`
+is an optional comma- or space-separated subset of the feature names in
+`.github/configs/feature.yaml`.
+
+With no `features`, an EIP branch rehearses the feature it releases for
+its own EIP and nothing else, and every other branch rehearses every
+feature. Either way a branch that adds a feature is covered without
+touching the workflow.
+
+Reuse `generate_build_matrix.py` so a rehearsal fills exactly what the
+release fills, then flatten the per-feature matrices into the single
+`fill_matrix` a `strategy.matrix` consumes.
+"""
+
+import json
+import re
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent))
+
+from generate_build_matrix import (  # noqa: E402
+    FEATURE_CONFIG,
+    FORK_RANGES_CONFIG,
+    build_matrix,
+    fail,
+    load_config,
+)
+
+# EIP branches follow `eips/<fork>/eip-<n>`, with `+` joining the EIP
+# numbers a combined branch carries, e.g. `eips/amsterdam/eip-2345+3456`.
+EIP_BRANCH_RE = re.compile(r"^eips/[^/]+/eip-([0-9]+(?:\+[0-9]+)*)$")
+
+
+def eip_features(defined: list[str], branch: str) -> list[str]:
+    """
+    Return the features *branch* releases for its own EIPs.
+
+    An EIP branch names its feature after the EIPs it carries, so
+    `eips/monad_next/eip-7997` releases `monad_eip7997` and
+    `eips/amsterdam/eip-2345+3456` releases `monad_eip2345+3456`. The
+    numbers must match in full: a combined branch does not claim the
+    feature of either EIP on its own, and neither claims the combined
+    one. Return an empty list for any other branch, and for an EIP
+    branch that has not declared a feature of its own yet.
+    """
+    match = EIP_BRANCH_RE.match(branch)
+    if not match:
+        return []
+    numbers = re.compile(rf"eip{re.escape(match.group(1))}(?![0-9+])")
+    return [name for name in defined if numbers.search(name)]
+
+
+def defined_features(config: dict) -> list[str]:
+    """Return every feature name in `feature.yaml`, in config order."""
+    return [
+        name for name, feature in config.items() if isinstance(feature, dict)
+    ]
+
+
+def select_features(config: dict, requested: str, branch: str) -> list[str]:
+    """
+    Narrow the rehearsal to the requested features.
+
+    An empty request falls back to the features *branch* releases for
+    its own EIPs, then to every feature: this fork releases all of
+    them. An unknown name fails the run rather than silently
+    rehearsing less than was asked for.
+    """
+    defined = defined_features(config)
+    names = [name for name in requested.replace(",", " ").split() if name]
+    if names:
+        unknown = [name for name in names if name not in defined]
+        if unknown:
+            fail(
+                f"unknown feature(s) {', '.join(unknown)}; "
+                f"{FEATURE_CONFIG} defines {', '.join(defined)}"
+            )
+        return names
+    from_branch = eip_features(defined, branch)
+    if from_branch:
+        print(
+            f"Branch '{branch}' releases {', '.join(from_branch)}; "
+            "rehearsing only that.",
+            file=sys.stderr,
+        )
+        return from_branch
+    return defined
+
+
+def main() -> None:
+    """Print the rehearsal's feature list and fill matrix to stdout."""
+    requested = sys.argv[1] if len(sys.argv) > 1 else ""
+    branch = sys.argv[2] if len(sys.argv) > 2 else ""
+
+    config = load_config(FEATURE_CONFIG)
+    fork_ranges = load_config(FORK_RANGES_CONFIG) or []
+
+    features = select_features(config, requested, branch)
+    if not features:
+        fail(f"{FEATURE_CONFIG} defines no feature")
+
+    matrix: list[dict] = []
+    for name in features:
+        entries, _ = build_matrix(config[name], name, fork_ranges)
+        matrix.extend(entries)
+
+    print(f"features={json.dumps(features)}")
+    print(f"fill_matrix={json.dumps(matrix)}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/.github/workflows/check_release.yaml b/.github/workflows/check_release.yaml
new file mode 100644
index 00000000000..8b1f7447b6f
--- /dev/null
+++ b/.github/workflows/check_release.yaml
@@ -0,0 +1,174 @@
+name: Check Fixture Release
+
+run-name: ${{ github.event_name == 'workflow_dispatch' && format('Check Fixture Release ({0}) {1}', inputs.depth, inputs.features) || 'Check Fixture Release' }}
+
+# Rehearse the fixture releases this fork ships, so a fill that a change
+# breaks surfaces on the branch that broke it rather than on the next
+# release attempt.
+#
+# Two tiers, both running on every pull request and on pushes to the
+# branches that release in parallel with the fork branch,
+# `from-upstream` and `eips/**`.
+#
+# `collect` is cheap: it reads the features the branch releases out of
+# `.github/configs/feature.yaml`, builds the release's job matrix
+# from it and collects its tests, catching malformed feature entries,
+# import errors and parametrization errors in a few minutes. It gates
+# `fill`, which is comprehensive: `fill` runs the very fill the release
+# runs, via the release's own action, and is the only tier that catches
+# a test that fills wrong. A manual dispatch can ask for `collect`
+# alone, and can narrow the run to a subset of the features.
+
+on:
+  push:
+    branches:
+      - from-upstream
+      - "eips/**"
+    paths-ignore:
+      - "**.md"
+      - "LICENSE*"
+      - ".gitignore"
+      - ".vscode/**"
+      - "whitelist.txt"
+      - "docs/**"
+      - "mkdocs.yml"
+  pull_request:
+    paths-ignore:
+      - "**.md"
+      - "LICENSE*"
+      - ".gitignore"
+      - ".vscode/**"
+      - "whitelist.txt"
+      - "docs/**"
+      - "mkdocs.yml"
+  workflow_dispatch:
+    inputs:
+      depth:
+        description: "full = fill every feature (hours); collect = validate the config and collect the tests (minutes)"
+        required: true
+        type: choice
+        options: [full, collect]
+        default: full
+      features:
+        description: "Features to rehearse, e.g. monad_runloop. Empty = an EIP branch's own feature, or every feature elsewhere."
+        required: false
+        type: string
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref || github.run_id }}
+  cancel-in-progress: ${{ github.ref_name != github.event.repository.default_branch }}
+
+permissions:
+  contents: read
+
+jobs:
+  setup:
+    runs-on: ubuntu-latest
+    outputs:
+      features: ${{ steps.matrix.outputs.features }}
+      fill_matrix: ${{ steps.matrix.outputs.fill_matrix }}
+      fill: ${{ steps.depth.outputs.fill }}
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          submodules: false
+      - uses: ./.github/actions/setup-uv
+
+      - name: Select the features to rehearse
+        id: matrix
+        shell: bash
+        env:
+          INPUT_FEATURES: ${{ inputs.features }}
+          # The head branch, so a pull request from an EIP branch
+          # rehearses that branch's feature; `ref_name` is the merge ref
+          # on a pull request and the branch everywhere else.
+          BRANCH: ${{ github.head_ref || github.ref_name }}
+        run: |
+          # The feature selection and the per-feature release matrix live
+          # in (and are shared with the release workflow via)
+          # check_release_matrix.py.
+          uv run -q .github/scripts/check_release_matrix.py \
+            "$INPUT_FEATURES" "$BRANCH" | tee -a "$GITHUB_OUTPUT"
+
+      - name: Decide whether to fill
+        id: depth
+        shell: bash
+        env:
+          EVENT: ${{ github.event_name }}
+          DEPTH: ${{ inputs.depth }}
+        run: |
+          # Every automatic trigger fills; only a dispatch can ask for
+          # the cheap tier alone.
+          if [ "$EVENT" = "workflow_dispatch" ] && [ "$DEPTH" != "full" ]
+          then
+            fill=false
+          else
+            fill=true
+          fi
+          echo "Fill: $fill"
+          echo "fill=$fill" >> "$GITHUB_OUTPUT"
+
+  collect:
+    name: collect (${{ matrix.feature }})
+    needs: setup
+    runs-on: ubuntu-24.04
+    timeout-minutes: 30
+    strategy:
+      # A rehearsal wants every feature's verdict, not the first failure.
+      fail-fast: false
+      matrix:
+        feature: ${{ fromJson(needs.setup.outputs.features) }}
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          submodules: true
+      - uses: ./.github/actions/setup-uv
+      - name: Install EEST
+        run: uv sync --no-progress
+
+      - name: Extract fixture release properties from config
+        id: properties
+        run: |
+          uv run -q .github/scripts/get_release_props.py ${{ matrix.feature }} >> "$GITHUB_OUTPUT"
+
+      - name: Collect the release's tests
+        shell: bash
+        run: |
+          # `fill-params` is interpolated rather than passed through a
+          # variable so its quoting survives, as in `build-fixtures`.
+          # Collecting nothing means an empty release, so pytest's exit
+          # code 5 fails here where a release's fork-range split
+          # tolerates it.
+          status=0
+          uv run fill --collect-only -q \
+            ${{ steps.properties.outputs.fill-params }} > collected.txt \
+            || status=$?
+          tail -n 20 collected.txt
+          exit "$status"
+
+  fill:
+    name: fill (${{ matrix.label || matrix.feature }})
+    needs: [setup, collect]
+    if: needs.setup.outputs.fill == 'true'
+    runs-on: ubuntu-24.04
+    # Hosted runners cap a job at six hours regardless; the explicit
+    # timeout keeps a wedged fill from burning the whole budget.
+    timeout-minutes: 360
+    strategy:
+      fail-fast: false
+      matrix:
+        include: ${{ fromJson(needs.setup.outputs.fill_matrix) }}
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          submodules: true
+
+      - uses: ./.github/actions/build-fixtures
+        with:
+          release_name: ${{ matrix.feature }}
+          from_fork: ${{ matrix.from_fork }}
+          until_fork: ${{ matrix.until_fork }}
+          split_label: ${{ matrix.label }}
+          # A rehearsal only reports whether the fill succeeds; keeping
+          # its fixtures would cost storage for output nothing consumes.
+          upload: "false"