diff --git a/.env.example b/.env.example
index 2cc0add02..66bb8c6fb 100644
--- a/.env.example
+++ b/.env.example
@@ -25,6 +25,10 @@ export AZURE_OPENAI_AUTH_MODE=api_key
 # export OPENAI_COMPATIBLE_BASE_URL=https://api.novita.ai/openai/v1
 # export OPENAI_COMPATIBLE_API_KEY=...
 # export OPENAI_COMPATIBLE_MODEL=zai-org/glm-5.2
+# Opper (OpenAI-compatible, EU-hosted) works the same way:
+# export OPENAI_COMPATIBLE_BASE_URL=https://api.opper.ai/v3/compat
+# export OPENAI_COMPATIBLE_API_KEY=...
+# export OPENAI_COMPATIBLE_MODEL=claude-sonnet-4-6
 # Per-role overrides use OPTIMIZER_OPENAI_COMPATIBLE_* and
 # TARGET_OPENAI_COMPATIBLE_* (BASE_URL, API_KEY, MODEL, TEMPERATURE,
 # MAX_TOKENS, TIMEOUT_SECONDS).
diff --git a/docs/guide/new-backend.md b/docs/guide/new-backend.md
index 07f6a1cc8..894beb525 100644
--- a/docs/guide/new-backend.md
+++ b/docs/guide/new-backend.md
@@ -29,6 +29,7 @@ A single `base_url` + `api_key` pair lets you point SkillOpt at, for example:
 | OpenRouter / Fireworks / xAI / … | provider base URL | provider model id |
 | OrcaRouter | `https://api.orcarouter.ai/v1` | `openai/gpt-5.5` |
 | Cheaper Inference | `https://api.cheaperinference.com/v1` | `gpt-5.4-mini` |
+| Opper | `https://api.opper.ai/v3/compat` | `claude-sonnet-4-6` |
 
 [OrcaRouter](https://www.orcarouter.ai) exposes OpenAI, Anthropic, Google,
 DeepSeek and other models behind one OpenAI-compatible endpoint. Its model IDs