diff --git a/skills/together-chat-completions/SKILL.md b/skills/together-chat-completions/SKILL.md
index a636ab5..de4024c 100644
--- a/skills/together-chat-completions/SKILL.md
+++ b/skills/together-chat-completions/SKILL.md
@@ -83,6 +83,8 @@ clearly offline batch processing, vector retrieval, model training, or infrastru
 - Tool names must not contain spaces, periods, or dashes. Branch on `finish_reason` (`"tool_calls"` vs `"stop"`) instead of assuming a tool was called, and parse `function.arguments` as JSON inside a try/except.
 - Prefer `json_schema` over looser JSON modes when the user needs stable machine-readable output.
 - Use reasoning models only when the task benefits from deeper deliberation; otherwise prefer cheaper standard models.
+- Preserved thinking uses the `reasoning` key on both output and input (the field is symmetric). When you pass a prior assistant turn back to the API, include `"reasoning": ...` on the assistant message; `reasoning_content` is still accepted on input for backward compatibility but prefer `reasoning` in new code.
+- Reasoning models nest extra token counts OpenAI-style (`usage.completion_tokens_details.reasoning_tokens`, `usage.prompt_tokens_details.cached_tokens`), but some non-reasoning models return `cached_tokens` flat at the top of `usage`. Read both locations defensively — clients that only check one shape will silently return `0`. See [references/reasoning-models.md](references/reasoning-models.md) for the defensive-read pattern.
 - To combine tool calling with structured output, use a two-phase approach: Phase 1 sends `tools` (no `response_format`), Phase 2 sends `response_format` (no `tools`) after tool results are appended.
 - Streaming works with `response_format`; accumulate chunks and parse the final concatenated string as JSON.
 - If the user needs many independent requests, combine this skill with `async_parallel.py` or hand off to batch inference.
diff --git a/skills/together-chat-completions/references/reasoning-models.md b/skills/together-chat-completions/references/reasoning-models.md
index 7d72f87..662723f 100644
--- a/skills/together-chat-completions/references/reasoning-models.md
+++ b/skills/together-chat-completions/references/reasoning-models.md
@@ -6,6 +6,7 @@
 - [Enabling and Disabling Reasoning (Hybrid Models)](#enabling-and-disabling-reasoning)
 - [Controlling Reasoning Depth via Prompting](#controlling-reasoning-depth-via-prompting)
 - [Reasoning Output Format](#reasoning-output-format)
+- [Tracking Reasoning and Cached Token Usage](#tracking-reasoning-and-cached-token-usage)
 - [Structured Outputs with Reasoning](#structured-outputs-with-reasoning)
 - [Best Practices by Model](#best-practices-by-model)
 
@@ -244,6 +245,11 @@ response = client.chat.completions.create(
 Models like Kimi K2.6, GLM-5.1, DeepSeek-V4-Pro, GPT-OSS, and Qwen3.5 return reasoning in a dedicated
 `reasoning` field on the response message or streaming delta.
 
+The field is symmetric: the model returns its chain of thought in `reasoning` (or `delta.reasoning`
+when streaming), and you pass it back under the same `reasoning` key when you send a prior assistant
+turn to the API for preserved thinking or multi-turn tool calling. The older `reasoning_content`
+key is still accepted on input for backward compatibility, but prefer `reasoning` for new code.
+
 **Non-streaming (Python):**
 
 ```python
@@ -306,6 +312,46 @@ for await (const chunk of stream) {
 }
 ```
 
+## Tracking Reasoning and Cached Token Usage
+
+Reasoning output is billed as completion tokens. The extra token counts (reasoning tokens, cached
+prompt tokens) always live somewhere on `response.usage`, but their **location varies by model**, so
+read both shapes defensively.
+
+- **Reasoning models** (for example `deepseek-ai/DeepSeek-V4-Pro`, `Qwen/Qwen3.6-Plus`,
+  `zai-org/GLM-5.1`) nest them OpenAI-style:
+  - `usage.completion_tokens_details.reasoning_tokens`
+  - `usage.prompt_tokens_details.cached_tokens`
+- **Some non-reasoning models** (for example `meta-llama/Llama-3.3-70B-Instruct-Turbo`) return
+  `cached_tokens` flat at the top level of `usage`, with no `*_details` objects.
+
+A client configured for only one shape will silently return `0` for all others. Fall back across
+both locations:
+
+```python
+usage = response.usage
+reasoning_tokens = (
+    getattr(usage, "completion_tokens_details", None)
+    and getattr(usage.completion_tokens_details, "reasoning_tokens", 0)
+) or 0
+
+cached_tokens = (
+    getattr(usage, "prompt_tokens_details", None)
+    and getattr(usage.prompt_tokens_details, "cached_tokens", 0)
+) or getattr(usage, "cached_tokens", 0)
+```
+
+```typescript
+const usage = response.usage as any;
+const reasoningTokens =
+  usage?.completion_tokens_details?.reasoning_tokens ?? 0;
+const cachedTokens =
+  usage?.prompt_tokens_details?.cached_tokens ?? usage?.cached_tokens ?? 0;
+```
+
+`prompt_tokens`, `completion_tokens`, and `total_tokens` are always present at the top level of
+`usage` regardless of model type.
+
 ## Structured Outputs with Reasoning
 
 Reasoning models support JSON mode for structured output extraction: