diff --git a/CHANGELOG.md b/CHANGELOG.md
index a3e7cc53b..66a2ca1f6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Features
+
+* **wrap:** `headroom wrap claude --1m` preserves the 1M context window. Behind a custom `ANTHROPIC_BASE_URL` (the proxy) Claude Code drops the `context-1m` beta header and caps the window at 200k for entitled subscription users; the opt-in flag sets `ANTHROPIC_MODEL=<opus>[1m]` on the launched process so the 1M window activates through Headroom. A model already selected via `ANTHROPIC_MODEL` is preserved (only the `[1m]` suffix is appended) ([#1158](https://github.com/chopratejas/headroom/issues/1158)).
+
 ### Changed
 
 * **telemetry:** anonymous usage telemetry is now **opt-in** (off by default) instead of opt-out. Nothing is collected or sent unless you set `HEADROOM_TELEMETRY=on` or pass `--telemetry` to `headroom proxy` / `headroom install apply`. `is_telemetry_enabled()` is fail-closed — only explicit on-values (`on`/`true`/`1`/`yes`/`enable`/`enabled`) enable it; unset, empty, or unrecognized values stay disabled. The existing `--no-telemetry` flag and `HEADROOM_TELEMETRY=off` remain accepted for back-compat, and install manifests now write the `HEADROOM_TELEMETRY` value explicitly so generated deployments are unambiguous.
diff --git a/README.md b/README.md
index f2903aad3..104c587d9 100644
--- a/README.md
+++ b/README.md
@@ -192,7 +192,7 @@ shows an **Output Tokens Saved** card next to input compression, labelled
 
 | Agent        | `headroom wrap` | Notes                            |
 |--------------|:---------------:|----------------------------------|
-| Claude Code  | ✅              | `--memory` · `--code-graph`      |
+| Claude Code  | ✅              | `--memory` · `--code-graph` · `--1m` |
 | Codex        | ✅              | shares memory with Claude        |
 | Cursor       | ✅              | prints config — paste once       |
 | Aider        | ✅              | starts proxy + launches          |
diff --git a/headroom/cli/wrap.py b/headroom/cli/wrap.py
index 2e1416e90..216073649 100644
--- a/headroom/cli/wrap.py
+++ b/headroom/cli/wrap.py
@@ -146,6 +146,29 @@ _TOOL_SEARCH_ENV = TOOL_SEARCH_ENV
 _TOOL_SEARCH_DEFAULT = TOOL_SEARCH_DEFAULT
 _AGENT_SAVINGS_WRAP_AGENTS = {"claude", "codex", "cursor"}
 
+# 1M context window for `wrap claude` (#1158). Claude Code only sends the
+# `context-1m` beta header — unlocking the 1M window for entitled subscription
+# users — when the model id carries the `[1m]` suffix. Behind a custom
+# ANTHROPIC_BASE_URL (the proxy) its `/model` picker selection does not survive,
+# so `--1m` forces the suffix via ANTHROPIC_MODEL on the launched process.
+_ANTHROPIC_MODEL_ENV = "ANTHROPIC_MODEL"
+_CONTEXT_1M_SUFFIX = "[1m]"
+# Only used when no model is otherwise selected (no ANTHROPIC_MODEL set). The
+# current default Opus; the suffix logic preserves any model the user did set.
+_DEFAULT_1M_MODEL = "claude-opus-4-8"
+
+
+def _resolve_1m_model(current: str | None) -> str:
+    """Return the model id that makes Claude Code request the 1M window (#1158).
+
+    Preserves a model the user already selected via ``ANTHROPIC_MODEL`` (only
+    appending the ``[1m]`` suffix when missing); falls back to the default Opus
+    when none is set. Idempotent — a value already ending in ``[1m]`` is
+    returned unchanged.
+    """
+    base = (current or "").strip() or _DEFAULT_1M_MODEL
+    return base if base.endswith(_CONTEXT_1M_SUFFIX) else f"{base}{_CONTEXT_1M_SUFFIX}"
+
 
 def _normalize_tool_search_mode(value: str) -> str:
     """Validate an ``ENABLE_TOOL_SEARCH`` value and return it normalized.
@@ -3086,6 +3109,17 @@ def unwrap() -> None:
     default=None,
     help="Cloud region for Vertex/Bedrock backends (env: HEADROOM_REGION).",
 )
+@click.option(
+    "--1m",
+    "context_1m",
+    is_flag=True,
+    help=(
+        "Preserve the 1M context window. Behind a custom ANTHROPIC_BASE_URL "
+        "Claude Code drops the context-1m beta header and caps at 200k; this "
+        "sets ANTHROPIC_MODEL=<opus>[1m] on the launched process so the 1M "
+        "window activates through the proxy (issue #1158)."
+    ),
+)
 @click.option("--verbose", "-v", is_flag=True, help="Verbose output")
 @click.option("--prepare-only", is_flag=True, hidden=True)
 @click.argument("claude_args", nargs=-1, type=click.UNPROCESSED)
@@ -3101,6 +3135,7 @@ def claude(
     tool_search: str | None,
     backend: str | None,
     region: str | None,
+    context_1m: bool,
     verbose: bool,
     prepare_only: bool,
     claude_args: tuple,
@@ -3121,6 +3156,7 @@ def claude(
         headroom wrap claude --no-context-tool  # Skip CLI context-tool setup
         headroom wrap claude --no-mcp           # Skip MCP retrieve tool registration
         headroom wrap claude --no-serena        # Skip Serena MCP registration
+        headroom wrap claude --1m               # Preserve the 1M context window
     """
     if prepare_only:
         if not no_rtk:
@@ -3321,6 +3357,16 @@ def claude(
                 "(using your existing environment value)"
             )
 
+        # Issue #1158: opt-in 1M context window. Claude Code only sends the
+        # context-1m beta header when the model id carries the [1m] suffix, so
+        # force it via ANTHROPIC_MODEL on the launched process.
+        if context_1m:
+            env[_ANTHROPIC_MODEL_ENV] = _resolve_1m_model(env.get(_ANTHROPIC_MODEL_ENV))
+            click.echo(
+                f"  {_ANTHROPIC_MODEL_ENV}={env[_ANTHROPIC_MODEL_ENV]} "
+                "(1M context window; issue #1158)"
+            )
+
         result = subprocess.run([claude_bin, *claude_args], env=env)
         raise SystemExit(result.returncode)
 
diff --git a/tests/test_cli/test_wrap_helpers.py b/tests/test_cli/test_wrap_helpers.py
index 5594a9d6c..87806e5e5 100644
--- a/tests/test_cli/test_wrap_helpers.py
+++ b/tests/test_cli/test_wrap_helpers.py
@@ -765,3 +765,27 @@ def test_ensure_proxy_already_running_prints_dashboard_url(
     output = _run_in_click_context(lambda: wrap_mod._ensure_proxy(port, no_proxy=False))
 
     assert f"http://127.0.0.1:{port}/dashboard" in output
+
+
+# ---------------------------------------------------------------------------
+# _resolve_1m_model — 1M context window suffix logic (#1158).
+# ---------------------------------------------------------------------------
+
+
+def test_resolve_1m_model_appends_suffix_to_user_model() -> None:
+    """A model the user already selected via ANTHROPIC_MODEL is preserved, with
+    only the [1m] suffix appended so Claude Code requests the 1M window."""
+    assert wrap_mod._resolve_1m_model("claude-opus-4-1-20250805") == (
+        "claude-opus-4-1-20250805[1m]"
+    )
+
+
+def test_resolve_1m_model_is_idempotent() -> None:
+    """A model that already carries [1m] is returned unchanged (no double suffix)."""
+    assert wrap_mod._resolve_1m_model("claude-opus-4-8[1m]") == "claude-opus-4-8[1m]"
+
+
+def test_resolve_1m_model_falls_back_to_default_when_unset() -> None:
+    """With no model selected, fall back to the default Opus carrying [1m]."""
+    assert wrap_mod._resolve_1m_model(None) == "claude-opus-4-8[1m]"
+    assert wrap_mod._resolve_1m_model("  ") == "claude-opus-4-8[1m]"