diff --git a/tests/wandb_interface/test_project_creator.py b/tests/wandb_interface/test_project_creator.py
index 27402627060e..43e73617cd15 100644
--- a/tests/wandb_interface/test_project_creator.py
+++ b/tests/wandb_interface/test_project_creator.py
@@ -5,6 +5,7 @@
 import pytest
 
 from weave.compat.wandb import AuthenticationError, CommError
+from weave.trace.settings import override_settings
 from weave.wandb_interface.project_creator import (
     UnableToCreateProjectError,
     ensure_project_exists,
@@ -138,6 +139,30 @@ def test_ensure_project_exists_authentication_error(mock_api_with_no_project):
     )
 
 
+def test_ensure_project_exists_autocreate_disabled_existing_project_ok(
+    mock_api_with_existing_project,
+):
+    """With autocreate disabled, an existing project still resolves normally."""
+    with override_settings(autocreate_project=False):
+        result = ensure_project_exists("test_entity", "test_project")
+
+    assert result == {"project_name": "existing_project"}
+    mock_api_with_existing_project.upsert_project.assert_not_called()
+
+
+def test_ensure_project_exists_autocreate_disabled_missing_project_errors(
+    mock_api_with_no_project,
+):
+    """With autocreate disabled, a missing project raises without upserting."""
+    with (
+        override_settings(autocreate_project=False),
+        pytest.raises(UnableToCreateProjectError, match="autocreate_project is disabled"),
+    ):
+        ensure_project_exists("test_entity", "test_project")
+
+    mock_api_with_no_project.upsert_project.assert_not_called()
+
+
 @pytest.mark.disable_logging_error_check
 def test_ensure_project_exists_comm_error(mock_api_with_no_project):
     """Test project creation with communication error."""
diff --git a/weave/trace/api.py b/weave/trace/api.py
index 6c6fc7745668..06f5417156e5 100644
--- a/weave/trace/api.py
+++ b/weave/trace/api.py
@@ -108,6 +108,9 @@ def init(
                     call data (start and end) into a single request instead of separate start/end requests.
                     This reduces server load and improves performance, especially for short-lived ops.
                     Default: `True`
+                - `autocreate_project` (bool): Allows `weave.init` to create the project on the
+                    server if it does not already exist. When `False`, `weave.init` raises an
+                    error instead of creating the project. Default: `True`
         autopatch_settings: (Deprecated) Configuration for autopatch integrations. Use explicit patching instead.
         postprocess_inputs: A function applied to the inputs of every op traced by this client.
         postprocess_output: A function applied to the output of every op traced by this client.
diff --git a/weave/trace/settings.py b/weave/trace/settings.py
index 8451c3acc121..0f8a46fd8f56 100644
--- a/weave/trace/settings.py
+++ b/weave/trace/settings.py
@@ -317,6 +317,16 @@ class UserSettings:
     Can be overridden with the environment variable `WEAVE_USE_OTEL_V2`
     """
 
+    autocreate_project: bool = True
+    """Toggles automatic project creation on `weave.init()`.
+
+    If True (default), `weave.init('entity/project')` upserts the project,
+    creating it on the server if it does not yet exist. If False, `weave.init`
+    raises `UnableToCreateProjectError` when the project does not exist; the
+    project must be created out-of-band (e.g. via the W&B UI).
+    Can be overridden with the environment variable `WEAVE_AUTOCREATE_PROJECT`
+    """
+
 
 class _SettingsOverrides(TypedDict, total=False):
     """Typed kwargs accepted by :func:`override_settings`.
@@ -360,6 +370,7 @@ class _SettingsOverrides(TypedDict, total=False):
     enable_wal: bool
     disable_wal_sender: bool
     use_otel_v2: bool
+    autocreate_project: bool
 
 
 # Resolve string annotations once at import; used for env-var coercion.
@@ -634,3 +645,10 @@ def should_disable_wal_sender() -> bool:
 def should_use_otel_v2() -> bool:
     """Returns whether OTel-capable integrations should use their OTel variant."""
     return _env_or_default("use_otel_v2", _current_settings.get().use_otel_v2)
+
+
+def should_autocreate_project() -> bool:
+    """Returns whether `weave.init` may create the project if it does not exist."""
+    return _env_or_default(
+        "autocreate_project", _current_settings.get().autocreate_project
+    )
diff --git a/weave/wandb_interface/project_creator.py b/weave/wandb_interface/project_creator.py
index 2c6d977f87bb..98ecd87f93c4 100644
--- a/weave/wandb_interface/project_creator.py
+++ b/weave/wandb_interface/project_creator.py
@@ -23,7 +23,11 @@
 
 from weave.compat import wandb
 from weave.compat.wandb import wandb_logger
-from weave.trace.settings import retry_max_attempts, retry_max_interval
+from weave.trace.settings import (
+    retry_max_attempts,
+    retry_max_interval,
+    should_autocreate_project,
+)
 
 
 class UnableToCreateProjectError(Exception): ...
@@ -120,6 +124,13 @@ def _ensure_project_exists(entity_name: str, project_name: str) -> dict[str, str
     if project_exception is not None:
         _raise_project_access_error(entity_name, project_name, project_exception)
 
+    if not should_autocreate_project():
+        raise UnableToCreateProjectError(
+            f"Project `{entity_name}/{project_name}` does not exist and "
+            "autocreate_project is disabled. Create the project in the W&B UI "
+            "or set WEAVE_AUTOCREATE_PROJECT=true."
+        )
+
     # Try to create the project
     exception = None
     try: