Document the flex service tier

chat/overview.mdx

@@ -167,7 +167,7 @@ The longer the conversation, the more tokens it uses. The maximum conversation l
 | `frequency_penalty` | Penalizes tokens based on how often they've appeared so far, reducing repetition. Range: -2.0 to 2.0. Default: `0` |
 | `response_format` | See [Structured Outputs](/chat/structured-outputs) |
 | `tools`, `tool_choice` | See [Tool Calling](/chat/tool-calling) |
-| `service_tier` | Priority inference for tagged models. See [Service Tier](#service-tier) below. |
+| `service_tier` | Select a service tier (`"priority"` or `"flex"`) for tagged models. See [Service Tier](#service-tier) below. |
 | `reasoning_effort` | Controls reasoning depth for reasoning models. See [Reasoning Models](/chat/reasoning). |
 
 <Note>
@@ -178,6 +178,10 @@ For the complete parameter reference, see the [API reference](/api-reference/cha
 
 ## Service tier
 
+Set the optional `service_tier` parameter to run a request on a non-standard tier. Two tiers are available on tagged models: **priority** (faster, at a premium) and **flex** (cheaper, best-effort). Leave `service_tier` unset for standard real-time scheduling and pricing.
+
+### Priority
+
 Set `service_tier` to `"priority"` to request priority inference on supported models. Priority requests get faster time-to-first-token and higher throughput during peak demand.
 
 <Warning>
@@ -220,7 +224,51 @@ curl "https://api.deepinfra.com/v1/openai/chat/completions" \
 
 </CodeGroup>
 
-The response includes a `service_tier` field confirming which tier was actually used. Not all models support priority tiers — check the model page for availability. If a model doesn't support priority inference, the request is served at the standard tier and billed at the standard price; no error is returned.
+### Flex
+
+Set `service_tier` to `"flex"` to run Chat Completions requests at a lower cost in exchange for slower response times and occasional resource unavailability. It's ideal for non-production or lower-priority tasks such as model evaluations, data enrichment, and asynchronous workloads. When a model is busy, a flex request may wait up to 10 minutes for available capacity before it runs or is rejected with an HTTP 429, so use it for work you can retry.
+
+<Note>
+  Flex inference is billed at a 20% discount off the model's standard per-token price.
+</Note>
+
+<CodeGroup>
+
+```python Python
+response = client.chat.completions.create(
+    model="deepseek-ai/DeepSeek-V3",
+    messages=[{"role": "user", "content": "Hello!"}],
+    extra_body={"service_tier": "flex"},
+)
+```
+
+```javascript JavaScript
+const response = await openai.chat.completions.create({
+  model: "deepseek-ai/DeepSeek-V3",
+  messages: [{ role: "user", content: "Hello!" }],
+  service_tier: "flex",
+});
+```
+
+```bash cURL
+curl "https://api.deepinfra.com/v1/openai/chat/completions" \
+  -H "Content-Type: application/json" \
+  -H "Authorization: Bearer $DEEPINFRA_TOKEN" \
+  -d '{
+      "model": "deepseek-ai/DeepSeek-V3",
+      "service_tier": "flex",
+      "messages": [
+        {
+          "role": "user",
+          "content": "Hello!"
+        }
+      ]
+    }'
+```
+
+</CodeGroup>
+
+The response includes a `service_tier` field confirming which tier was actually used. Not all models support these tiers — check the model page for availability. If a model doesn't support the requested tier, the request is served at the standard tier and billed at the standard price; no error is returned.
 
 ## Max output tokens