diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index e332b12..6f4202f 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -32,7 +32,7 @@ jobs:
 
       - name: Install Python dependencies
         working-directory: libs/openant-core
-        run: pip install -r requirements.txt && pip install pytest ruff
+        run: pip install -e ".[dev]"
 
       - name: Lint Python (undefined names, syntax errors)
         working-directory: libs/openant-core
@@ -44,7 +44,7 @@ jobs:
 
       - name: Run Python and parser tests
         working-directory: libs/openant-core
-        run: python -m pytest tests/test_token_tracker.py tests/test_parser_adapter.py tests/test_python_parser.py tests/test_js_parser.py tests/test_resume_stage1.py -v
+        run: python -m pytest tests/test_token_tracker.py tests/test_parser_adapter.py tests/test_python_parser.py tests/test_js_parser.py tests/test_resume_stage1.py tests/test_declared_dependencies.py -v
 
   go-tests:
     name: Go build + integration (${{ matrix.os }})
@@ -99,7 +99,7 @@ jobs:
 
       - name: Install Python dependencies
         working-directory: libs/openant-core
-        run: pip install -r requirements.txt && pip install pytest
+        run: pip install -e ".[dev]"
 
       - name: Install JS parser dependencies
         working-directory: libs/openant-core/parsers/javascript
diff --git a/libs/openant-core/README.md b/libs/openant-core/README.md
index fdc2d80..81062dc 100644
--- a/libs/openant-core/README.md
+++ b/libs/openant-core/README.md
@@ -24,7 +24,7 @@ git clone https://github.com/your-org/openant.git
 cd openant
 
 # Install Python dependencies
-pip install -r requirements.txt
+pip install -e .
 
 # Set API key
 echo "ANTHROPIC_API_KEY=your-key-here" > .env
diff --git a/libs/openant-core/pyproject.toml b/libs/openant-core/pyproject.toml
index 34ffb1c..8f3d935 100644
--- a/libs/openant-core/pyproject.toml
+++ b/libs/openant-core/pyproject.toml
@@ -5,6 +5,7 @@ description = "Two-stage SAST tool using Claude for vulnerability analysis"
 readme = "README.md"
 requires-python = ">=3.11"
 dependencies = [
+    "anthropic>=0.40.0",
     "claude-agent-sdk>=0.1.48",
     "python-dotenv>=1.0.0",
     "pydantic>=2.0.0",
@@ -16,6 +17,7 @@ dependencies = [
     "tree-sitter-cpp>=0.21.0",
     "tree-sitter-ruby>=0.21.0",
     "tree-sitter-php>=0.22.0",
+    "tree-sitter-zig>=0.20.0",
 ]
 
 [project.optional-dependencies]
diff --git a/libs/openant-core/requirements.txt b/libs/openant-core/requirements.txt
deleted file mode 100644
index 966904a..0000000
--- a/libs/openant-core/requirements.txt
+++ /dev/null
@@ -1,24 +0,0 @@
-annotated-types==0.7.0
-anthropic==0.75.0
-anyio==4.12.0
-certifi==2025.11.12
-distro==1.9.0
-docstring_parser==0.17.0
-h11==0.16.0
-httpcore==1.0.9
-httpx==0.28.1
-idna==3.11
-jiter==0.12.0
-pydantic==2.12.5
-pydantic_core==2.41.5
-python-dotenv==1.2.1
-sniffio==1.3.1
-typing-inspection==0.4.2
-typing_extensions==4.15.0
-PyYAML>=6.0
-requests>=2.31.0
-tree-sitter>=0.21.0
-tree-sitter-c>=0.21.0
-tree-sitter-cpp>=0.21.0
-tree-sitter-ruby>=0.21.0
-tree-sitter-php>=0.22.0
diff --git a/libs/openant-core/tests/test_declared_dependencies.py b/libs/openant-core/tests/test_declared_dependencies.py
new file mode 100644
index 0000000..103d34e
--- /dev/null
+++ b/libs/openant-core/tests/test_declared_dependencies.py
@@ -0,0 +1,127 @@
+"""Guard against pyproject.toml declared deps drifting from actual imports.
+
+Regression guard for the Claude Agent SDK migration (#25), which dropped
+`anthropic` from pyproject.toml while leaving `import anthropic` live in
+four files. Every clean install of openant broke at `openant parse`.
+"""
+import ast
+import sys
+import tomllib
+from pathlib import Path
+
+import pytest
+
+PROJECT_ROOT = Path(__file__).parent.parent
+PACKAGED_DIRS = ["openant", "core", "utilities", "parsers", "prompts", "context", "report"]
+
+# Maps PyPI distribution names to their top-level import names when they differ.
+# Extend only when adding a new dependency whose import name diverges from its
+# PyPI name; the test will tell you which direction it's failing.
+DIST_TO_IMPORT = {
+    "python-dotenv": "dotenv",
+    "pyyaml": "yaml",
+    "claude-agent-sdk": "claude_agent_sdk",
+    "tree-sitter": "tree_sitter",
+    "tree-sitter-c": "tree_sitter_c",
+    "tree-sitter-cpp": "tree_sitter_cpp",
+    "tree-sitter-ruby": "tree_sitter_ruby",
+    "tree-sitter-php": "tree_sitter_php",
+}
+
+
+def _dist_name_to_import(dist: str) -> str:
+    key = dist.lower().replace("_", "-")
+    return DIST_TO_IMPORT.get(key, dist.replace("-", "_").lower())
+
+
+def _declared_imports() -> set[str]:
+    with open(PROJECT_ROOT / "pyproject.toml", "rb") as f:
+        data = tomllib.load(f)
+    deps = data["project"]["dependencies"]
+    names = []
+    for dep in deps:
+        for sep in ("[", ">=", "<=", "==", "!=", ">", "<", "~=", ";", " "):
+            dep = dep.split(sep, 1)[0]
+        names.append(dep.strip())
+    return {_dist_name_to_import(n) for n in names if n}
+
+
+def _collect_top_level_imports(root: Path) -> set[str]:
+    """Return the set of top-level module names imported anywhere under `root`."""
+    imports: set[str] = set()
+    for py in root.rglob("*.py"):
+        try:
+            tree = ast.parse(py.read_text(encoding="utf-8"))
+        except (SyntaxError, UnicodeDecodeError):
+            continue
+        for node in ast.walk(tree):
+            if isinstance(node, ast.Import):
+                for alias in node.names:
+                    imports.add(alias.name.split(".", 1)[0])
+            elif isinstance(node, ast.ImportFrom):
+                # Relative imports (level > 0) have module=None or point at a
+                # sibling — they can't be third-party by definition.
+                if node.level == 0 and node.module:
+                    imports.add(node.module.split(".", 1)[0])
+    return imports
+
+
+def _first_party_names() -> set[str]:
+    """Every module/package name reachable in the repo — treated as first-party.
+
+    Parsers use sys.path hackery to import siblings as top-level names
+    (e.g. `from call_graph_builder import ...`), so the set of first-party
+    names isn't just the packaged top-level dirs.
+    """
+    names: set[str] = set(PACKAGED_DIRS)
+    for path in PROJECT_ROOT.rglob("*.py"):
+        # Skip the managed dev venv and any other nested virtualenvs.
+        if ".venv" in path.parts or "site-packages" in path.parts:
+            continue
+        names.add(path.stem)
+        for parent in path.parents:
+            if parent == PROJECT_ROOT:
+                break
+            names.add(parent.name)
+    return names
+
+
+def test_every_third_party_import_is_declared():
+    first_party = _first_party_names()
+    stdlib = set(sys.stdlib_module_names)
+    declared = _declared_imports()
+
+    all_imports: set[str] = set()
+    for pkg in PACKAGED_DIRS:
+        pkg_dir = PROJECT_ROOT / pkg
+        if pkg_dir.is_dir():
+            all_imports |= _collect_top_level_imports(pkg_dir)
+
+    # Deps pulled in transitively that some callsites import by name. These
+    # aren't direct deps of openant but are guaranteed present by something
+    # we *do* declare, so it's safe to treat them as allowed.
+    transitive_allowed = {
+        # pulled in by claude-agent-sdk
+        "mcp",
+    }
+
+    third_party = all_imports - first_party - stdlib - transitive_allowed
+    missing = sorted(third_party - declared)
+    assert not missing, (
+        f"Imports not declared in pyproject.toml dependencies: {missing}. "
+        "Either add the distribution to `dependencies`, or remove the import. "
+        "If a distribution's import name differs from its PyPI name, add it to "
+        "DIST_TO_IMPORT in this test."
+    )
+
+
+@pytest.mark.parametrize("pkg", PACKAGED_DIRS)
+def test_package_imports_cleanly(pkg):
+    """Smoke-test: every packaged top-level module can be imported.
+
+    This catches the specific failure mode from #25 — where a dropped dep
+    only manifested at `import utilities` time, not at `import openant`.
+    """
+    if not (PROJECT_ROOT / pkg).is_dir():
+        pytest.skip(f"{pkg} not present")
+    __import__(pkg)