docs: chat-completions is now a compat shim on Router, not a 404

Router shipped a minimal /v1/chat/completions compatibility surface
(translated onto Responses) after this PR was written, so the
'does not exist and 404s' wording is stale. Responses remains the
native wire — per-model reasoning-effort validation, reasoning
summaries, and prompt caching live there — so the api.router.com
host mandate is unchanged; only the comments and docs are updated.

cli-config.yaml.example

@@ -152,10 +152,11 @@ model:
 #   router:
 #     base_url: https://api.router.com/v1
 #     api_key: ${RAMP_ROUTER_API_KEY}
-#     # api_mode auto-detected as codex_responses for api.router.com — the host
-#     # is Responses-only (/v1/chat/completions 404s). The bundled router
-#     # provider covers this; a named custom provider is only needed for a
-#     # non-default Router-compatible endpoint.
+#     # api_mode auto-detected as codex_responses for api.router.com — the
+#     # Responses API is Router's native wire (chat/completions is only a
+#     # compatibility shim). The bundled router provider covers this; a named
+#     # custom provider is only needed for a non-default Router-compatible
+#     # endpoint.
 
 
 # Command-minted credentials (optional): key_cmd

hermes_cli/providers.py

@@ -663,8 +663,10 @@ def host_mandated_api_mode(base_url: str = "") -> Optional[str]:
       - api.meta.ai only achieves KV-cache hits on /v1/responses with
         prompt_cache_retention; /v1/chat/completions returns 0 cached
         tokens (measured 0% vs 93-99% on /responses with retention).
-      - api.router.com (Ramp Router) implements ONLY the Responses API —
-        POST /v1/chat/completions does not exist on the host and 404s.
+      - api.router.com (Ramp Router) is Responses-native: per-model
+        reasoning-effort validation, reasoning summaries, and prompt
+        caching live on /v1/responses; /v1/chat/completions is only a
+        minimal compatibility shim translated onto it.
       - api.anthropic.com / ``…/anthropic`` suffixes speak native Messages.
       - Kimi's ``/coding`` endpoint speaks native Messages.
       - AWS Bedrock runtime hosts speak Converse.
@@ -697,9 +699,11 @@ def host_mandated_api_mode(base_url: str = "") -> Optional[str]:
     # cache-cold (0% vs 93-99% measured). Exact-hostname match per #32243.
     if hostname == "api.meta.ai":
         return "codex_responses"
-    # Ramp Router (api.router.com) is Responses-only: the host serves
-    # GET /v1/models and POST /v1/responses, and /v1/chat/completions 404s
-    # (docs.router.com/api/endpoint). Exact-hostname match per #32243.
+    # Ramp Router (api.router.com) is Responses-native: reasoning-effort
+    # validation, reasoning summaries, and prompt caching live on
+    # /v1/responses, and /v1/chat/completions is only a minimal
+    # compatibility shim (docs.router.com/api/endpoint). Exact-hostname
+    # match per #32243.
     if hostname == "api.router.com":
         return "codex_responses"
     if hostname.startswith("bedrock-runtime.") and base_url_host_matches(base_url, "amazonaws.com"):

hermes_cli/runtime_provider.py

@@ -163,8 +163,9 @@ def _detect_api_mode_for_url(base_url: str) -> Optional[str]:
         return "codex_responses"
     if hostname == "api.actual.inc":
         return "codex_responses"
-    # Ramp Router: Responses-only host — /v1/chat/completions does not
-    # exist and 404s (docs.router.com/api/endpoint). Mirrors the
+    # Ramp Router: Responses-native host — /v1/chat/completions is only a
+    # minimal compatibility shim, while reasoning and caching support live
+    # on /v1/responses (docs.router.com/api/endpoint). Mirrors the
     # host_mandated_api_mode clause in hermes_cli/providers.py so the
     # runtime resolver stays in lockstep. Exact hostname per #32243.
     if hostname == "api.router.com":

plugins/model-providers/router/__init__.py

@@ -8,10 +8,14 @@ spend controls server-side.
 
 Wire notes (verified live against api.router.com, Aug 2026):
 
-* **Responses API only.** Router implements ``GET /v1/models`` and
-  ``POST /v1/responses``; ``POST /v1/chat/completions`` does not exist and
-  404s. ``api_mode="codex_responses"`` plus the ``api.router.com`` host
-  mandate in ``hermes_cli/providers.py`` keep every path off the chat wire.
+* **Responses API is the native wire.** Router serves ``GET /v1/models``
+  and ``POST /v1/responses``; ``POST /v1/chat/completions`` is only a
+  minimal compatibility shim (added Aug 2026) that translates onto
+  Responses. Per-model reasoning-effort validation, reasoning summaries,
+  and prompt caching are Responses-surface features, so
+  ``api_mode="codex_responses"`` plus the ``api.router.com`` host mandate
+  in ``hermes_cli/providers.py`` keep every path on the native wire —
+  the same shape as the ``api.openai.com`` mandate.
 * **Account-scoped catalog.** Valid model IDs are whatever the key's
   ``GET /v1/models`` returns (BYOK accounts see extra entries), so this
   profile ships **no** ``fallback_models`` — the picker relies on the live

tests/hermes_cli/test_router_provider.py

@@ -1,7 +1,8 @@
 """Behavior contracts for the Ramp Router (api.router.com) provider.
 
-Router is Responses-only: the host implements GET /v1/models and
-POST /v1/responses, and POST /v1/chat/completions does not exist (404).
+Router is Responses-native: the host implements GET /v1/models and
+POST /v1/responses, and /v1/chat/completions is only a minimal
+compatibility shim translated onto Responses.
 These tests pin the host mandate, the runtime URL detection that mirrors
 it, and the profile/auth registry wiring — same contract suite shape as
 tests/hermes_cli/test_meta_prompt_cache.py.

website/docs/developer-guide/adding-providers.md

@@ -35,7 +35,7 @@ The important abstraction is `api_mode`.
 
 - Most providers use `chat_completions`.
 - Codex and Meta Model API (`api.meta.ai` — Muse Spark) use `codex_responses` (auto-sends `prompt_cache_retention: 24h` for prompt caching; `api.meta.ai` achieves 93–99% cache hits only on `/v1/responses`).
-- Ramp Router (`api.router.com`) also uses `codex_responses` — the host is Responses-only (`/v1/chat/completions` 404s) and validates `reasoning.effort` per model, which the router profile handles by declaring each model's vocabulary from the live catalog (`ProviderProfile.supported_reasoning_efforts`).
+- Ramp Router (`api.router.com`) also uses `codex_responses` — Responses is Router's native wire (`/v1/chat/completions` is only a minimal compatibility shim), and it validates `reasoning.effort` per model, which the router profile handles by declaring each model's vocabulary from the live catalog (`ProviderProfile.supported_reasoning_efforts`).
 - Anthropic uses `anthropic_messages`.
 - A new non-OpenAI protocol usually means adding a new adapter and a new `api_mode` branch.