diff --git a/CHANGELOG.md b/CHANGELOG.md
index e2a7907..1e1dc3c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
# Hermes Web UI -- Changelog
+## [v0.50.53] — 2026-04-15
+
+### Fixed
+- **Custom endpoint slash model IDs** — model IDs with vendor prefixes that are intrinsic (e.g. `zai-org/GLM-5.1` on DeepInfra) are now preserved when routing to a custom `base_url` endpoint. Previously, all prefixed IDs were stripped, causing `model_not_found` errors on providers that require the full vendor/model format. Known provider namespaces (`openai/`, `google/`, `anthropic/`, etc.) are still stripped as before. (Fixes #548, PR #549 by @eba8)
+
## [v0.50.52] — 2026-04-15
### Fixed
diff --git a/api/config.py b/api/config.py
index 39101d6..2f83a11 100644
--- a/api/config.py
+++ b/api/config.py
@@ -637,10 +637,14 @@ def resolve_model_provider(model_id: str) -> tuple:
# just because the model name contains a slash (e.g. google/gemma-4-26b-a4b).
# The user has explicitly pointed at a base_url, so trust their routing config.
if config_base_url:
- # Strip provider prefix (e.g. 'openai/gpt-5.4' -> 'gpt-5.4') so prefixed
- # model IDs from previous sessions don't break custom endpoint routing.
- bare_model = model_id.split('/', 1)[-1]
- return bare_model, config_provider, config_base_url
+ # Only strip the provider prefix when it's a known provider namespace
+ # (e.g. "openai/gpt-5.4" → "gpt-5.4" for a custom OpenAI-compatible proxy).
+ # Unknown prefixes (e.g. "zai-org/GLM-5.1" on DeepInfra) are intrinsic to
+ # the model ID and must be preserved — stripping them causes model_not_found.
+ if prefix in _PROVIDER_MODELS:
+ return bare, config_provider, config_base_url
+ # Unknown prefix (not a named provider) — pass full model_id through.
+ return model_id, config_provider, config_base_url
# If prefix does NOT match config provider, the user picked a cross-provider model
# from the OpenRouter dropdown (e.g. config=anthropic but picked openai/gpt-5.4-mini).
# In this case always route through openrouter with the full provider/model string.
diff --git a/static/index.html b/static/index.html
index 522466a..63786c1 100644
--- a/static/index.html
+++ b/static/index.html
@@ -553,7 +553,7 @@