diff --git a/CHANGELOG.md b/CHANGELOG.md
index 89fc5d9d0..63fc25a25 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Fixed
+
+- **Codex: `CLIENT_UA_MAP` matched a User-Agent no shipped Codex build sends.**
+  The only OpenAI needle was `codex-cli/`; measured across two `proxy.log`
+  rotations the Codex User-Agents actually on the wire were `codex-tui/` (3,167
+  requests), `codex-browser-use/` (1,338), `Codex Desktop/` (368),
+  `codex_cli_rs/` (13) and `codex-computer-use/` (1) — 4,887 requests, zero
+  matches. Every Codex request therefore classified as `None`, so the Codex
+  fail-open in `decide_compression_failure_action()`, which keys on
+  `client == "codex"`, never fired and a compression timeout returned 413.
+
 ### Features
 - **proxy:** opt-in cost-aware model routing ([#1706](https://github.com/headroomlabs-ai/headroom/issues/1706)). Set `HEADROOM_MODEL_ROUTER_ENABLED=1` and `HEADROOM_MODEL_ROUTES` (a JSON array of ordered rules) to rewrite the upstream model based on estimated input size and tool presence, complementary to content compression, e.g. send small, tool-free requests to a cheaper model. First matching rule wins, and each decision is logged with a reason so routing stays observable. Malformed rules fail open (the rule is skipped, never silently widened). Disabled by default so behavior is unchanged, skipped under `x-headroom-bypass`/passthrough, and currently applied on the Anthropic `/v1/messages` path.
 - **install:** `headroom install apply` now accepts `--code-aware/--no-code-aware`, `--intercept-tool-results`, `--protect-tool-results`, and `--bedrock-profile`, mirroring the equivalent flags already on `headroom proxy`. Previously the only way to run a persistent deployment with these settings was to hand-edit `manifest.json` after the fact, which silently reverts on the next `install apply`.
diff --git a/headroom/proxy/auth_policy.py b/headroom/proxy/auth_policy.py
index 73f6cf91d..71ed103cf 100644
--- a/headroom/proxy/auth_policy.py
+++ b/headroom/proxy/auth_policy.py
@@ -33,6 +33,11 @@ CLIENT_UA_MAP: tuple[tuple[str, str], ...] = (
     ("claude-vscode/", "claude-vscode"),
     ("anthropic-cli/", "anthropic-cli"),
     ("codex-cli/", "codex"),
+    ("codex-tui/", "codex"),
+    ("codex_cli_rs/", "codex"),
+    ("codex-browser-use/", "codex"),
+    ("codex-computer-use/", "codex"),
+    ("codex desktop/", "codex"),
     ("cursor/", "cursor"),
     ("grok/", "grok_build"),
     ("zed/", "zed"),
diff --git a/tests/test_auth_mode_codex_user_agents.py b/tests/test_auth_mode_codex_user_agents.py
new file mode 100644
index 000000000..eb21bbb06
--- /dev/null
+++ b/tests/test_auth_mode_codex_user_agents.py
@@ -0,0 +1,84 @@
+"""Codex User-Agent classification regression tests (AQ-0610).
+
+``CLIENT_UA_MAP`` carried a single OpenAI needle, ``codex-cli/``, which no
+shipped Codex build actually sends. Every Codex request therefore classified as
+``None``, so the Codex-specific fail-open in ``headroom/proxy/helpers.py`` —
+which keys on ``client == "codex"`` — never fired and the proxy answered a
+compression timeout with 413. Codex treats 413 as fatal, so sessions died at
+startup.
+
+The User-Agent strings below are verbatim from ~/.headroom/logs/proxy.log, not
+invented. Counts across two rotations at the time of the fix:
+    codex-tui/           3,167
+    codex-browser-use/   1,338
+    Codex Desktop/         368
+    codex_cli_rs/           13
+    codex-computer-use/      1
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from headroom.proxy.auth_mode import classify_client
+
+# Verbatim User-Agents observed on the wire.
+OBSERVED_CODEX_USER_AGENTS = [
+    "codex-tui/0.147.0 (Mac OS 26.5.1; arm64) Apple_Terminal/470.2 (codex-tui; 0.147.0)",
+    "codex-tui/0.148.0-alpha.9 (Mac OS 26.5.1; arm64) xterm-256color",
+    "codex_cli_rs/0.147.0 (Mac OS 26.5.1; arm64) Apple_Terminal/470.2",
+    "codex_cli_rs/0.148.0-alpha.9 (Mac OS 26.5.1; arm64) unknown",
+    "codex-browser-use/0.147.0-alpha.1.2 (Mac OS 26.5.1; arm64) xterm-256color"
+    " (codex-browser-use; 0.1.0)",
+    "Codex Desktop/0.147.0-alpha.6.5 (Mac OS 26.5.1; arm64) unknown",
+    "Codex Desktop/0.148.0-alpha.9 (Mac OS 26.5.1; arm64) unknown (Codex Desktop; 26.810.41047)",
+    "codex-computer-use/0.147.0-alpha.1.2 (Mac OS 26.5.1; arm64) unknown",
+]
+
+
+@pytest.mark.parametrize("user_agent", OBSERVED_CODEX_USER_AGENTS)
+def test_observed_codex_user_agents_classify_as_codex(user_agent: str) -> None:
+    """Every Codex build seen in production must resolve to ``codex``.
+
+    This is what gates the compression-timeout fail-open. A ``None`` here means
+    a real Codex session gets a fatal 413 instead of an uncompressed forward.
+    """
+    assert classify_client({"user-agent": user_agent}) == "codex"
+
+
+def test_codex_desktop_matches_despite_capitals_and_space() -> None:
+    """``Codex Desktop/`` is the only client whose UA contains a space.
+
+    Matching lowercases the UA, so the needle must be lowercase too — a
+    ``"Codex Desktop/"`` needle would silently never match.
+    """
+    assert classify_client({"user-agent": "Codex Desktop/0.148.0-alpha.9 (Mac OS)"}) == "codex"
+
+
+def test_codex_ua_carrying_a_claude_code_originator_still_classifies_as_codex() -> None:
+    """Real UA that embeds both harness names.
+
+    ``codex_cli_rs/... (claude-code; 2.1.233)`` is the Codex binary reporting
+    Claude Code as its originator. The Anthropic needles are checked first and
+    require ``claude-code/`` with a slash, so the semicolon form must not steal
+    this match — the process talking to us is Codex, and Codex is the one that
+    dies on a 413.
+    """
+    ua = "codex_cli_rs/0.147.0 (Mac OS 26.5.1; arm64) Apple_Terminal/470.2 (claude-code; 2.1.233)"
+
+    assert classify_client({"user-agent": ua}) == "codex"
+
+
+def test_claude_code_user_agents_are_unaffected() -> None:
+    """Negative control: the Anthropic needles must keep winning their own UAs."""
+    assert classify_client({"user-agent": "claude-cli/2.1.233 (external, cli)"}) == "claude-code"
+    assert (
+        classify_client({"user-agent": "claude-cli/2.1.233 (external, sdk-py, agent-sdk/0.2.139)"})
+        == "claude-code"
+    )
+
+
+def test_unrelated_user_agent_still_returns_none() -> None:
+    """Negative control: broadening the Codex needles must not swallow everything."""
+    assert classify_client({"user-agent": "Mozilla/5.0 (Macintosh)"}) is None
+    assert classify_client({"user-agent": "curl/8.7.1"}) is None